Re: [Emc-users] Yet another topic about gantry homing

[andy pugh]

On Sat, 6 Oct 2018 at 15:02, Leonardo Marsaglia  wrote:

> As you pointed out Les, an hydraulic rod is what I'm planning to use. Hard
> chromed and also lubed to avoid premature wear.

Maybe motorcycle fork bushes (PTFE typically, on a metal backing)
would make good bearings.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916


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Re: [Emc-users] Yet another topic about gantry homing

[Jon Elson]

On 10/05/2018 11:17 PM, Roland Jollivet wrote:

Of course you can remove the nut. You just roll it onto a correctly sized
former.

In fact it's a good idea to do this with the linear slides and ballscrews
from china, to give them a wash. While they are greased up and wrapped in
plastic, they are often covered in grinding grit which won't help the
longevity of your drive system.


A trick I've used to clean a ballscrew and nut is to smear 
axle grease on the screw and run the nut across the greased 
region.  You will get lots of unhappy noises.  Then, wipe 
the grease off the screw, regrease and run the nut to the 
opposite end.  Inspect the wiped off grease for sparkles, 
that is the ground-off steel that was trapped in the nut.  
Repeat until the crunching noises stop and you don't see the 
sparkles in the wiped-off grease.  Then, you know it is 
pretty clean inside.


This is less nerve-wracking that taking it apart and 
wondering if it has alternate-sized balls or any other 
tricks in it.


Jon


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Re: [Emc-users] Yet another topic about gantry homing

[Gene Heskett]

On Saturday 06 October 2018 08:46:35 Les Newell wrote:

> > No, I plan to support 50 mm bars every 600 mm more or less. I'm
> > attaching some pictures of the design I'm working on
>
> If you really want to go with this I would second Chris' suggestion of
> using HDPE or UHMW. You are still gonna wear those shafts out pretty
> quick unless you use chromed shafts. Hydraulic rod is hard chromed and
> accurate diameter. I don't know if you can get 50mm hydraulic rod in
> those lengths but if you can it would still be pretty costly. The
> bushes will be service items so make plenty of spares!
>
> >   I also thought about
> > reducing the 3000 max RPM with the worm and gear to 100 RPM on the
> > shaft
>
> Don't use a worm or planetary gearbox. They have backlash (especially
> worm boxes) and don't like repeated drive reversal. Harmonic drives
> work well but don't have enough advantages to offset the cost in this
> application.
> You are looking for an overall 10:1 ratio so that can be done by two
> belt reductions. Say 3.2:1 from the motor to the shaft then another
> 3.2:1 from the shaft to the pinions. Cheap, simple and reliable.
>
> > I uploaded the pictures because the list doesn't allow me to attach
> > them. Here's the link: https://imgur.com/a/7kLUWsq
>
> I'd like to see some triangulation in that frame.  Try to make sure
> the screw/rack/whatever is well below the top of the table. You want
> to be able to easily slide sheets on and off the table without fear of
> damaging anything.
>
> In my opinion screws are out unless you use high pitch screws, say at
> least 25mm pitch, 30+ mm diameter. Even with rotating nuts there are
> limits to how fast you can spin the nut before the balls start jamming
> in their guides.
> I have used endless belts with a fixed motor, as Roland suggested, on
> a couple of machines. One was a 2.5m x 1.5m table machine and I had
> problems with the long belts flapping around, especially when changing
> direction. This was a plasma cutter so there wasn't much load. The
> other machine was a 3.5m long feeder which only needed to push
> accurately in one direction before retracting. I didn't have any
> problems with the belt flapping but stretch under load was a
> significant issue. On the plus side, that machine has been running
> every day for 10+ years with no noticeable wear in the drive system.
> Using a belt that is fixed at both ends and looped over the pulley is
> more than twice as rigid as an endless belt and it won't suffer from
> the flapping issues. For a machine your size I'd use two 30mm wide
> belts on X with lots of tension. I really like the servo belt idea and
> am thinking of using it on a machine I am planning on building.
> Keeping dirt out could be an issue.
> I have serviced a lot of commercial CNC routers and generally they
> either use high pitch screws or rack.
>
> Todd suggested a minimum of 5KW for the spindle. It does depend a lot
> on what you are doing. You can do a lot with a 1/2" cutter which will
> work fine on a 3KW spindle. If you want to go bigger you will need
> more power. Don't forget about extraction. You'll be generating a LOT
> of dust. Making a good extraction hood isn't nearly as easy as you
> would first think. If you need multiple tools for each job you might
> want to allow for a tool changer. If you can't have a tool changer at
> least have a tool setter. Tool setters are easy enough to make and
> save a lot of time. Just make sure it is well protected so you can't
> damage it when loading/unloading sheets.
>
> > If indeed its that critical, one would need a dynamic distance
> > detection method of some sort riding the work pretty close to the
> > tool...
>
> Whoa Gene, before you get too esoteric the solution is actually really
> cheap and simple. Make the top of the table out of something that is
> easy to machine, say MDF or plastic. After building and leveling the
> machine skim the whole table using the router. The distance from Z to
> the table will be pretty darn accurate over the whole area. As long as
> the machine is built reasonably accurately the table will be pretty
> close to flat. Remember this is a wood router, probably cutting large
> sheets. If the machine has a slight bow the sheets will bend enough to
> sit flat on the table, especially if it is a vacuum table.
>
> This brings up another point. How do you intend to hold the work down?
> The simplest solution is to have a MDF bed and screw your work down
> but that can get old fast if you are working with big sheets,
> especially if you are cutting lots of different parts. You only need
> one miss placed screw to wreck a cutter and probably the job as well.
> Vacuum works well. There are two options. The first is a pod system.
> You have a number of vacuum pods like these .
> They use a high vacuum and hold well but are best suited to production
> work on pre-cut blanks where you can set up and run hundreds or
> thousands of parts. A 

Re: [Emc-users] Yet another topic about gantry homing

[Leonardo Marsaglia]

A lot of discussion! I love this list haha.

Well, I will try to answer this and focus on the main subjects we've been
covering.

As you pointed out Les, an hydraulic rod is what I'm planning to use. Hard
chromed and also lubed to avoid premature wear. I plan to add some sort of
plate to collect the oil so it's not dripping all around the machine. They
are costly, but they are made here in Argentina, as opose to the linear
guides that we've been discussing. And since our currency suffered a severe
devaluation in the last months, there are some components that are a lot
cheaper to buy in here.

About not using bronze, is this only because of the wear? Or do you think
it will behave worse than  HDPE or UHMW?

The reduction I thought of originally was two step down timing pulleys and
then the pinion connected to rack to give me the 10 to 1 ratio. I would
like also to add an encoder directly coupled to the pinions for position
feedback and may be compensate the backlash by software. I've been reading
about using two pinions one fixed and the other spring loaded to cancel out
the backlash but I think it's easier to cancel it in LinuxCNC. I've already
done that on a grinder and works pretty well. Off course the rack on that
grinder is far more precise than the one I'm going to use here, but this is
for wood and melamine and I can allow some inaccuracies.

Spindle, yes I thought about using 3 to 5 kw. I'm mostly going to use 1/4"
to 1/2" diameter mills to cut through melamine. I'm still thinking about
adding an ATC but I think that part will come later, because to start,
there's not much work that needs a lot of tools. The ATC will have the
tools resting on a side and that's one of the reasons the machine has 3.8
meters long in the work surface. Since the longer sheet we may use is about
3.6 meters long. The extra space is for the tool fixture.

About the work holding subject. Yes, the idea is to use vacuum. I didn't
calculate yet what amount of power we might need but It's good to have your
expertise in here. The idea is to use what you mentioned, an MDF table wich
is where the air is going to be suck from and take a skim cut to level the
table. Here's a link of something similar from what I want to do:
https://www.youtube.com/watch?v=fOrkvPF0pro

It's a little difficult to answer one by one since I don't have quoting
anymore but I thank all of you for your inputs and expertise!




El sáb., 6 oct. 2018 a las 9:47, Les Newell ()
escribió:

> > No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
> > some pictures of the design I'm working on
>
> If you really want to go with this I would second Chris' suggestion of
> using HDPE or UHMW. You are still gonna wear those shafts out pretty
> quick unless you use chromed shafts. Hydraulic rod is hard chromed and
> accurate diameter. I don't know if you can get 50mm hydraulic rod in
> those lengths but if you can it would still be pretty costly. The bushes
> will be service items so make plenty of spares!
>
> >   I also thought about
> > reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
>
> Don't use a worm or planetary gearbox. They have backlash (especially
> worm boxes) and don't like repeated drive reversal. Harmonic drives work
> well but don't have enough advantages to offset the cost in this
> application.
> You are looking for an overall 10:1 ratio so that can be done by two
> belt reductions. Say 3.2:1 from the motor to the shaft then another
> 3.2:1 from the shaft to the pinions. Cheap, simple and reliable.
>
> > I uploaded the pictures because the list doesn't allow me to attach them.
> > Here's the link: https://imgur.com/a/7kLUWsq
>
> I'd like to see some triangulation in that frame.  Try to make sure the
> screw/rack/whatever is well below the top of the table. You want to be
> able to easily slide sheets on and off the table without fear of
> damaging anything.
>
> In my opinion screws are out unless you use high pitch screws, say at
> least 25mm pitch, 30+ mm diameter. Even with rotating nuts there are
> limits to how fast you can spin the nut before the balls start jamming
> in their guides.
> I have used endless belts with a fixed motor, as Roland suggested, on a
> couple of machines. One was a 2.5m x 1.5m table machine and I had
> problems with the long belts flapping around, especially when changing
> direction. This was a plasma cutter so there wasn't much load. The other
> machine was a 3.5m long feeder which only needed to push accurately in
> one direction before retracting. I didn't have any problems with the
> belt flapping but stretch under load was a significant issue. On the
> plus side, that machine has been running every day for 10+ years with no
> noticeable wear in the drive system.
> Using a belt that is fixed at both ends and looped over the pulley is
> more than twice as rigid as an endless belt and it won't suffer from the
> flapping issues. For a machine your size I'd use two 30mm wide 

Re: [Emc-users] Yet another topic about gantry homing

[Les Newell]

No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
some pictures of the design I'm working on


If you really want to go with this I would second Chris' suggestion of 
using HDPE or UHMW. You are still gonna wear those shafts out pretty 
quick unless you use chromed shafts. Hydraulic rod is hard chromed and 
accurate diameter. I don't know if you can get 50mm hydraulic rod in 
those lengths but if you can it would still be pretty costly. The bushes 
will be service items so make plenty of spares!



  I also thought about
reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft


Don't use a worm or planetary gearbox. They have backlash (especially 
worm boxes) and don't like repeated drive reversal. Harmonic drives work 
well but don't have enough advantages to offset the cost in this 
application.
You are looking for an overall 10:1 ratio so that can be done by two 
belt reductions. Say 3.2:1 from the motor to the shaft then another 
3.2:1 from the shaft to the pinions. Cheap, simple and reliable.



I uploaded the pictures because the list doesn't allow me to attach them.
Here's the link: https://imgur.com/a/7kLUWsq


I'd like to see some triangulation in that frame.  Try to make sure the 
screw/rack/whatever is well below the top of the table. You want to be 
able to easily slide sheets on and off the table without fear of 
damaging anything.


In my opinion screws are out unless you use high pitch screws, say at 
least 25mm pitch, 30+ mm diameter. Even with rotating nuts there are 
limits to how fast you can spin the nut before the balls start jamming 
in their guides.
I have used endless belts with a fixed motor, as Roland suggested, on a 
couple of machines. One was a 2.5m x 1.5m table machine and I had 
problems with the long belts flapping around, especially when changing 
direction. This was a plasma cutter so there wasn't much load. The other 
machine was a 3.5m long feeder which only needed to push accurately in 
one direction before retracting. I didn't have any problems with the 
belt flapping but stretch under load was a significant issue. On the 
plus side, that machine has been running every day for 10+ years with no 
noticeable wear in the drive system.
Using a belt that is fixed at both ends and looped over the pulley is 
more than twice as rigid as an endless belt and it won't suffer from the 
flapping issues. For a machine your size I'd use two 30mm wide belts on 
X with lots of tension. I really like the servo belt idea and am 
thinking of using it on a machine I am planning on building. Keeping 
dirt out could be an issue.
I have serviced a lot of commercial CNC routers and generally they 
either use high pitch screws or rack.


Todd suggested a minimum of 5KW for the spindle. It does depend a lot on 
what you are doing. You can do a lot with a 1/2" cutter which will work 
fine on a 3KW spindle. If you want to go bigger you will need more 
power. Don't forget about extraction. You'll be generating a LOT of 
dust. Making a good extraction hood isn't nearly as easy as you would 
first think. If you need multiple tools for each job you might want to 
allow for a tool changer. If you can't have a tool changer at least have 
a tool setter. Tool setters are easy enough to make and save a lot of 
time. Just make sure it is well protected so you can't damage it when 
loading/unloading sheets.



If indeed its that critical, one would need a dynamic distance detection
method of some sort riding the work pretty close to the tool...


Whoa Gene, before you get too esoteric the solution is actually really 
cheap and simple. Make the top of the table out of something that is 
easy to machine, say MDF or plastic. After building and leveling the 
machine skim the whole table using the router. The distance from Z to 
the table will be pretty darn accurate over the whole area. As long as 
the machine is built reasonably accurately the table will be pretty 
close to flat. Remember this is a wood router, probably cutting large 
sheets. If the machine has a slight bow the sheets will bend enough to 
sit flat on the table, especially if it is a vacuum table.


This brings up another point. How do you intend to hold the work down? 
The simplest solution is to have a MDF bed and screw your work down but 
that can get old fast if you are working with big sheets, especially if 
you are cutting lots of different parts. You only need one miss placed 
screw to wreck a cutter and probably the job as well.
Vacuum works well. There are two options. The first is a pod system. You 
have a number of vacuum pods like these . They 
use a high vacuum and hold well but are best suited to production work 
on pre-cut blanks where you can set up and run hundreds or thousands of 
parts. A matrix bed pulls a vacuum through the whole bed. They rely on 
high flow and a lower vacuum. They are best for sheet work, especially 
if you run lots of different parts. You 

Re: [Emc-users] Yet another topic about gantry homing

[Gene Heskett]

On Saturday 06 October 2018 00:56:58 Gene Heskett wrote:

> On Friday 05 October 2018 23:24:38 Chris Albertson wrote:
> > A third option is a REALLY long belt.  It is long enough to make a
> > double pass on each side and needs about 8 pulleys but you only need
> > one motor.  I saw one of these once but it used a kevlar cable, not
> > a belt
> >
> > I think the shaft is move simple but but you need precision
> > mechanics to adjust it.  It is ever comes apart for service you'd
> > need some good measuring tools to align it.But with two motors
> > the adjustment misdone in software and the mechanic doing the
> > service only needs to get it "close" by eyeball with a tape measure.
> > find adjustment is later in software.
> >
> > My dirt cheap 3D printer uses two motors and parallel screws and I
> > use basically a sheet of paper as a feeler gauge and I can reset
> > alignment in abut 30 seconds to about 0.005 mm.
> >
> > Any design can work as long as you have a designed on squaring
> > method that can be done with simple/cheap tools
> >
> > All the talk about the long axis but I think the REALLY hard part is
> > the Z axis.  Lets say you make a cut that is 0.15 mm deep and 3
> > meters long. Will it remain exactly 0.15mm deep over that long
> > distance?   I bet you a buck not.
>
> No takers on that bet Chris.
>
> If indeed its that critical, one would need a dynamic distance
> detection method of some sort riding the work pretty close to the
> tool, which would be outputting the instant offset, and would be
> driving the Z to maintain that distance in real time. And the success
> of that would be in building it to not be material sensitive, or
> subject to getting tangled with the cuttings.
>
> Because it has to operate in a pretty noisy environment, I'd design it
> with a hardened ball pointed lever, sitting the ball quite close to
> the tool, and pivoting a couple inches away from the cutter, with the
> far end moving a ferrite slug in and out of a coil which was part of
> an oscillator running at 100+ kilohertz, and some sort of a frequency
> discriminator, possibly a crystal referenced phase locked loop, using
> the pll's error as the signal into an offset module.  With the correct
> gain, I'd say you could make a working correction circuit that would
> reduce a 5mm error to +- .01mm, which might be close enough. That
> wouldn't care how long or wide the bed and workpiece are but the lever
> should be constrained from dropping over the edge of the workpiece and
> being caught and destroyed. That implies a bigger ball. The ferrite
> slug could be moved by a small wire thru a hole in the shielding so
> other electrical noises wouldn't bither it too much, or were fast
> enough that the drive motor will function as a noise integrator. This
> could be centered in the control range by useing a screw the pivot
> point up and down with a hand knob, on the levers pivot point height.
> With the tool stopped, adjust the slider with the rest of the circuit
> live, so the tool touches the work or holds a paper slip, then dial an
> offset in with a sum2 to drive the tool to the desired depth.  And
> apply just enough shop air to keep the contact area 99% clean.
>
> Theres probably a few more ways to skin that cat, as all of this would
> have to be moved with the z drive, but thats what I'd try since the
> electronics are fairly well understood here at the coyote.den. Making
> the hardware would take me some longer than some of you. But I'd get
> it done as long as I'm still looking at the green side of the grass.
> ;-) Not having the real estate for a big gantry machine would slow me
> down I expect.


Nother idea. Put the air into a small pipe that nearly touches the work, 
feed it enough air to be self cleaning, and the air pressure backup 
because of it close proximity to the work would be fed to a barometer 
chip to measure the back pressure, and feed that to the offset module. 
That would be more sensitive to the clearance and air gap from previous 
machining it was crossing over, so that would likely be impractical. 

Also highly non-linear because of the square law as it applies to that 
sort of thing and moving air. Not well taught is the fact that a 
motorized louver is flowing 50% of its wide open flow when its opened 
10%, or only 8 degrees from completely closed.

The only other idea I could come up with would be to map the face of the 
work area prior to doing any cutting. If the code was generated by a 
cad/cam proggy, the resultant gcode could have its z modulated with an 
intermediate processing utility using the previously mapped data for 
that xy point.

I've not played with the file idea because I've not figured out how to 
use the file method cross axis. LinuxCNC has not been setup to use 
correction files for anything but correcting its own screw errors for 
that same axis. To use the lincurve and offset modules for something 
like this would need a lincurve with 64 to 128 points on a 

Re: [Emc-users] Yet another topic about gantry homing

[Gene Heskett]

On Friday 05 October 2018 23:24:38 Chris Albertson wrote:

> A third option is a REALLY long belt.  It is long enough to make a
> double pass on each side and needs about 8 pulleys but you only need
> one motor.  I saw one of these once but it used a kevlar cable, not a
> belt
>
> I think the shaft is move simple but but you need precision mechanics
> to adjust it.  It is ever comes apart for service you'd need some good
> measuring tools to align it.But with two motors the adjustment
> misdone in software and the mechanic doing the service only needs to
> get it "close" by eyeball with a tape measure. find adjustment is
> later in software.
>
> My dirt cheap 3D printer uses two motors and parallel screws and I use
> basically a sheet of paper as a feeler gauge and I can reset alignment
> in abut 30 seconds to about 0.005 mm.
>
> Any design can work as long as you have a designed on squaring method
> that can be done with simple/cheap tools
>
> All the talk about the long axis but I think the REALLY hard part is
> the Z axis.  Lets say you make a cut that is 0.15 mm deep and 3 meters
> long. Will it remain exactly 0.15mm deep over that long distance?   I
> bet you a buck not.
>
No takers on that bet Chris.

If indeed its that critical, one would need a dynamic distance detection 
method of some sort riding the work pretty close to the tool, which 
would be outputting the instant offset, and would be driving the Z to 
maintain that distance in real time. And the success of that would be in 
building it to not be material sensitive, or subject to getting tangled 
with the cuttings.

Because it has to operate in a pretty noisy environment, I'd design it 
with a hardened ball pointed lever, sitting the ball quite close to the 
tool, and pivoting a couple inches away from the cutter, with the far 
end moving a ferrite slug in and out of a coil which was part of an 
oscillator running at 100+ kilohertz, and some sort of a frequency 
discriminator, possibly a crystal referenced phase locked loop, using 
the pll's error as the signal into an offset module.  With the correct 
gain, I'd say you could make a working correction circuit that would 
reduce a 5mm error to +- .01mm, which might be close enough. That 
wouldn't care how long or wide the bed and workpiece are but the lever 
should be constrained from dropping over the edge of the workpiece and 
being caught and destroyed. That implies a bigger ball. The ferrite slug 
could be moved by a small wire thru a hole in the shielding so other 
electrical noises wouldn't bither it too much, or were fast enough that 
the drive motor will function as a noise integrator. This could be 
centered in the control range by useing a screw the pivot point up and 
down with a hand knob, on the levers pivot point height. With the tool 
stopped, adjust the slider with the rest of the circuit live, so the 
tool touches the work or holds a paper slip, then dial an offset in with 
a sum2 to drive the tool to the desired depth.  And apply just enough 
shop air to keep the contact area 99% clean.

Theres probably a few more ways to skin that cat, as all of this would 
have to be moved with the z drive, but thats what I'd try since the 
electronics are fairly well understood here at the coyote.den. Making 
the hardware would take me some longer than some of you. But I'd get it 
done as long as I'm still looking at the green side of the grass.
;-) Not having the real estate for a big gantry machine would slow me 
down I expect.

-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 


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Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

A third option is a REALLY long belt.  It is long enough to make a double
pass on each side and needs about 8 pulleys but you only need one motor.  I
saw one of these once but it used a kevlar cable, not a belt

I think the shaft is move simple but but you need precision mechanics to
adjust it.  It is ever comes apart for service you'd need some good
measuring tools to align it.But with two motors the adjustment misdone
in software and the mechanic doing the service only needs to get it "close"
by eyeball with a tape measure. find adjustment is later in software.

My dirt cheap 3D printer uses two motors and parallel screws and I use
basically a sheet of paper as a feeler gauge and I can reset alignment in
abut 30 seconds to about 0.005 mm.

Any design can work as long as you have a designed on squaring method that
can be done with simple/cheap tools

All the talk about the long axis but I think the REALLY hard part is the Z
axis.  Lets say you make a cut that is 0.15 mm deep and 3 meters long.
Will it remain exactly 0.15mm deep over that long distance?   I bet you a
buck not.


.


> In any case I'm still not sure about wheter use two motors or one motor
> > with a shaft. The latter option makes me feel more secure because it
> can't
> > go out of squaress easily, unless you have loose belt or something
> breaks.
>
-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

They are on ebay.   Yousearch for "ball screw" and they come up.

Here is an example: https://www.ebay.com/itm/SFU1204-RM-Rolled-Ball-Screw

Here is another: ebay.com/itm/CNC-SFU1605-Ball-Screw



Notice the number "1204" this means 12mm diameter by 4mm pitch.  the other
common size is 1605.

You can look up there specs on Google by searching for SFU1204
specification and find the data.   When you do yo find that even a 12mm
screw has some inside strength like 1,000 pounds or soothing but that does
not matter the real limit is how fast you can spin the screw before it
"whips". Yo can NEVER remove the nut.  So design accordingly.

the other thing is that the balls are held in compression.  there is a
spring inside the nut so there is rolling resistance because the balls are
under load.   This is good because it removes backlash but I bet you'd see
balls shooting all over the shop if the nut came off the end.

The 1204 size is nice because with a normal 400 step motor it you run half
steps the each is exactly 0.005mm and that is good enough for a milling
machine. (works out to two 10ths in US units)

One more "got-ya" the two "flats" on either side of the nut are not flat it
is a taper.  It is good they did this but I did not notice at first.

On Fri, Oct 5, 2018 at 8:11 AM Dave Cole  wrote:

> Chris,
>
> Do you have a link for these "new style ball screws" ??
>
> Thanks,  Dave
>
> On 10/4/2018 3:33 PM, Chris Albertson wrote:
> > Have you seen the new style ball screws?   They are now cheaper then
> belts
> > and have pretty "over kill" specs.
> >
> > The problem with a 30mm wide belt drive is the need to resist  the belt
> > tension and a way to adjust it.   Not only the tension between the two
> > pulleys but there is side load on the motor shaft unless you use a
> flexible
> > coupler and ball bearings on both sides of the drive pulley.  The
> lead
> > screw is mechanically simpler because the motor can be directly coupled
> to
> > the screw and for $70 you get all the end blocks and mounting hardware.
> > These have made router design nearly a "screw driver only" project.  No
> > design to even much thinking needed.   I bought one for the vertical axis
> > of a CNC milling machine and I can set there is zero backlash and not
> > adjust needed or the life of the machine.  Cost me about $35.
> >
> > A screw give the drive motor a larger mechanical deduction and you can
> > likely skip the need for a reduction stage.  A screw might advance the
> axis
> > 4mm per revolution but a belt drive moves maybe 30 to 36mm per rev.
> >   You get more force the resolution with a 4mm pitch ball screw.
> >
> > You can make a one meter square X,Y router base or laser cutter today
> using
> > two pair of supported rails and two screws for under $250 plus the motors
> > and your z-axis.
> >
> > On Thu, Oct 4, 2018 at 11:41 AM Roland Jollivet <
> roland.jolli...@gmail.com>
> > wrote:
> >
> >> The idea of using belts, and gearboxes, and rack and pinions, sounds
> like a
> >> bad recipe.
> >>
> >> While I did suggest a bar across the gantry, the problem is that you're
> >> carrying all those gears, and the motor.
> >> I drew a quick concept sketch of how I would do it. Buy cut-to-length
> belt,
> >> probably HTD M5  x  30mm wide for your application.
> >>
> >> I think this would be quite adequate for a wood router. At the far end
> of
> >> the table, connect the two idler pulleys with a shaft too. Obviously all
> >> the pulleys and motors will be below the table height.
> >>
> >> And;
> >> - motor is no longer on the gantry
> >> - no skew can happen
> >> - easy to get your drive ratio
> >> - single motor
> >>
> >> http://imgbox.com/ccZJF5nH
> >>
> >>
> >>
> >> On Thu, 4 Oct 2018 at 17:41, Leonardo Marsaglia 
> >> wrote:
> >>
> >>> Hello Les,
> >>>
> >>> No, I plan to support 50 mm bars every 600 mm more or less. I'm
> attaching
> >>> some pictures of the design I'm working on. (The adjustable stands for
> >>> levelling are not in the assembly because I'm saving resources on this
> >>> laptop)
> >>>
> >>> I like the idea of using the rectangular ways but unfortunately they
> are
> >>> quite expensive for this project and also there's the aligning problem.
> >>> With the setup I'm trying to do I can adjust the parallelism on every
> >>> corner of the machine and also individually adjust every suport to
> level
> >>> the guides perfectly. I'm sending pictures of everything to clarify
> what
> >>> I'm intending to do. Please note 

Re: [Emc-users] Yet another topic about gantry homing

[Gene Heskett]

On Friday 05 October 2018 11:12:01 Dave Cole wrote:

> Chris,
>
> Do you have a link for these "new style ball screws" ??

Just do a google search. The prices seem to be in freefall. The 1 start, 
25x5x1450mm screw and nut, with bearings I paid right close to $180 usd 
+ ship, about $200, for the Z drive on my 11" sheldon, can now be had 
for about $80 USD with free shipping.

Smaller, & shorter screws are down to beer money, still with free 
shipping. I'm amazed.  And I'd nearly bet the thrust bearings are tight 
to start with instead of 10 thou of sloppy backlash/endplay in what I 
bought. I finally did find a round tuit and added 10 thou of shims 
between the outer races of the AC bearings, a bit much, but I just 
brought the nut up to a wee bit of preload and locked the screw. Z lash 
is now around 1.1 thou.


> Thanks,  Dave
>
> On 10/4/2018 3:33 PM, Chris Albertson wrote:
> > Have you seen the new style ball screws?   They are now cheaper then
> > belts and have pretty "over kill" specs.
> >
> > The problem with a 30mm wide belt drive is the need to resist  the
> > belt tension and a way to adjust it.   Not only the tension between
> > the two pulleys but there is side load on the motor shaft unless you
> > use a flexible coupler and ball bearings on both sides of the drive
> > pulley.  The lead screw is mechanically simpler because the
> > motor can be directly coupled to the screw and for $70 you get all
> > the end blocks and mounting hardware. These have made router design
> > nearly a "screw driver only" project.  No design to even much
> > thinking needed.   I bought one for the vertical axis of a CNC
> > milling machine and I can set there is zero backlash and not adjust
> > needed or the life of the machine.  Cost me about $35.
> >
> > A screw give the drive motor a larger mechanical deduction and you
> > can likely skip the need for a reduction stage.  A screw might
> > advance the axis 4mm per revolution but a belt drive moves maybe 30
> > to 36mm per rev. You get more force the resolution with a 4mm pitch
> > ball screw.
> >
> > You can make a one meter square X,Y router base or laser cutter
> > today using two pair of supported rails and two screws for under
> > $250 plus the motors and your z-axis.
> >
> > On Thu, Oct 4, 2018 at 11:41 AM Roland Jollivet
> > 
> >
> > wrote:
> >> The idea of using belts, and gearboxes, and rack and pinions,
> >> sounds like a bad recipe.
> >>
> >> While I did suggest a bar across the gantry, the problem is that
> >> you're carrying all those gears, and the motor.
> >> I drew a quick concept sketch of how I would do it. Buy
> >> cut-to-length belt, probably HTD M5  x  30mm wide for your
> >> application.
> >>
> >> I think this would be quite adequate for a wood router. At the far
> >> end of the table, connect the two idler pulleys with a shaft too.
> >> Obviously all the pulleys and motors will be below the table
> >> height.
> >>
> >> And;
> >> - motor is no longer on the gantry
> >> - no skew can happen
> >> - easy to get your drive ratio
> >> - single motor
> >>
> >> http://imgbox.com/ccZJF5nH
> >>
> >>
> >>
> >> On Thu, 4 Oct 2018 at 17:41, Leonardo Marsaglia
> >> 
> >>
> >> wrote:
> >>> Hello Les,
> >>>
> >>> No, I plan to support 50 mm bars every 600 mm more or less. I'm
> >>> attaching some pictures of the design I'm working on. (The
> >>> adjustable stands for levelling are not in the assembly because
> >>> I'm saving resources on this laptop)
> >>>
> >>> I like the idea of using the rectangular ways but unfortunately
> >>> they are quite expensive for this project and also there's the
> >>> aligning problem. With the setup I'm trying to do I can adjust the
> >>> parallelism on every corner of the machine and also individually
> >>> adjust every suport to level the guides perfectly. I'm sending
> >>> pictures of everything to clarify what I'm intending to do. Please
> >>> note this is under development and some
> >>
> >> things
> >>
> >>> are going to change a little bit.
> >>>
> >>> The idea of welding the frame is out of discussion because I plan
> >>> to move and set up this thing in place. Also, I don't have the
> >>> means to
> >>
> >> guarantee a
> >>
> >>> clean and squared welding for the frame. Instead I decided to do
> >>> what you can see in the pictures, having an enormous amount of
> >>> bolts to keep the parts rigid and firm.
> >>>
> >>> No problem about using tubing to lower the inertia. I also thought
> >>> about reducing the 3000 max RPM with the worm and gear to 100 RPM
> >>> on the shaft and then increase the size of the pinions to have the
> >>> linear speed I
> >>
> >> want.
> >>
> >>> This way the long shaft doesn't have to withstand the high RPMs.
> >>>
> >>> I uploaded the pictures because the list doesn't allow me to
> >>> attach them. Here's the link:
> >>>
> >>> https://imgur.com/a/7kLUWsq
> >>
> >> ___
> >> Emc-users mailing list
> >> Emc-users@lists.sourceforge.net
> >> 

Re: [Emc-users] Yet another topic about gantry homing

[Dave Cole]

By the time you buy the timing belts, pulleys, shafts, machine the 
brackets, to do a double belt reduction to get to 10:1, you are money 
ahead to just buy a servo grade 10:1 gearbox.    If you mount a pinion 
directly to the gearbox shaft and drive the rack with this pinion, you 
will have a very rigid drive system.


There are things like this out there.
https://www.ebay.com/itm/planetary-reducer-gearbox-3-1-to-10-1-for-1kw-2kw-130-AC-servo-motor-input-22mm/263810208961?hash=item3d6c5054c1:g:dFAAAOSwBd1bRsP1

If you buying Chinese servo motors and drives, ask them about a 10:1 
gearbox.


Dave

On 10/4/2018 11:13 AM, Leonardo Marsaglia wrote:

Hello Dave,

Well, to avoid the backlash is that or may be using timing belts and
pulleys to drive the shaft too. The gearbox is a good idea but I think that
can raise the cost too much. Anyway I'll give it a look because I don't
want to discard any option.

In any case I'm still not sure about wheter use two motors or one motor
with a shaft. The latter option makes me feel more secure because it can't
go out of squaress easily, unless you have loose belt or something breaks.

  By the way I just re send another message that was rejected by the list
because of the size of the pictures, I don't know if now you can see it.



El jue., 4 oct. 2018 a las 12:04, Leonardo Marsaglia ()
escribió:


Hello Les,

No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
some pictures of the design I'm working on. (The adjustable stands for
levelling are not in the assembly because I'm saving resources on this
laptop)

I like the idea of using the rectangular ways but unfortunately they are
quite expensive for this project and also there's the aligning problem.
With the setup I'm trying to do I can adjust the parallelism on every
corner of the machine and also individually adjust every suport to level
the guides perfectly. I'm sending pictures of everything to clarify what
I'm intending to do. Please note this is under development and some things
are going to change a little bit.

The idea of welding the frame is out of discussion because I plan to move
and set up this thing in place. Also, I don't have the means to guarantee a
clean and squared welding for the frame. Instead I decided to do what you
can see in the pictures, having an enormous amount of bolts to keep the
parts rigid and firm.

No problem about using tubing to lower the inertia. I also thought about
reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
and then increase the size of the pinions to have the linear speed I want.
This way the long shaft doesn't have to withstand the high RPMs.

(Second attempt to attach the pictures)

El jue., 4 oct. 2018 a las 12:00, Dave Cole ()
escribió:


I'd avoid a worm gear drive.   They are prone to wear and backlash.
I'd look for a good deal on a servo grade planetary 10:1 gearbox that
fits your Chinese motor.
Probably the easiest and most rigid drive solution is to use two motors
each with a planetary gear box and direct drive a pinion on a rack.
If you want to mill aluminum and need rigidity, that's the way I would go.
You might want to weld the frame in sections and then bolt it together.
If you don't have a platen to weld it on, you might want to contract out
part of the frame welding.

Dave

On 10/4/2018 10:41 AM, Leonardo Marsaglia wrote:

By the way, on the pictures there are missing details I didn't draw yet,
like setscrews for parallel regulation and things like that. Also, I

have

yet to modify the design for the one motor and shaft approach and see

wich

is better.

El jue., 4 oct. 2018 a las 11:37, Leonardo Marsaglia (<

ldmarsag...@gmail.com>)

escribió:


Hello Les,

No, I plan to support 50 mm bars every 600 mm more or less. I'm

attaching

some pictures of the design I'm working on. (The adjustable stands for
levelling are not in the assembly because I'm saving resources on this
laptop)

I like the idea of using the rectangular ways but unfortunately they

are

quite expensive for this project and also there's the aligning problem.
With the setup I'm trying to do I can adjust the parallelism on every
corner of the machine and also individually adjust every suport to

level

the guides perfectly. I'm sending pictures of everything to clarify

what

I'm intending to do. Please note this is under development and some

things

are going to change a little bit.

The idea of welding the frame is out of discussion because I plan to

move

and set up this thing in place. Also, I don't have the means to

guarantee a

clean and squared welding for the frame. Instead I decided to do what

you

can see in the pictures, having an enormous amount of bolts to keep the
parts rigid and firm.

No problem about using tubing to lower the inertia. I also thought

about

reducing the 3000 max RPM with the worm and gear to 100 RPM on the

shaft

and then increase the size of the pinions to have the linear speed I

want.

This way the long 

Re: [Emc-users] Yet another topic about gantry homing

[Dave Cole]

Chris,

Do you have a link for these "new style ball screws" ??

Thanks,  Dave

On 10/4/2018 3:33 PM, Chris Albertson wrote:

Have you seen the new style ball screws?   They are now cheaper then belts
and have pretty "over kill" specs.

The problem with a 30mm wide belt drive is the need to resist  the belt
tension and a way to adjust it.   Not only the tension between the two
pulleys but there is side load on the motor shaft unless you use a flexible
coupler and ball bearings on both sides of the drive pulley.  The lead
screw is mechanically simpler because the motor can be directly coupled to
the screw and for $70 you get all the end blocks and mounting hardware.
These have made router design nearly a "screw driver only" project.  No
design to even much thinking needed.   I bought one for the vertical axis
of a CNC milling machine and I can set there is zero backlash and not
adjust needed or the life of the machine.  Cost me about $35.

A screw give the drive motor a larger mechanical deduction and you can
likely skip the need for a reduction stage.  A screw might advance the axis
4mm per revolution but a belt drive moves maybe 30 to 36mm per rev.
  You get more force the resolution with a 4mm pitch ball screw.

You can make a one meter square X,Y router base or laser cutter today using
two pair of supported rails and two screws for under $250 plus the motors
and your z-axis.

On Thu, Oct 4, 2018 at 11:41 AM Roland Jollivet 
wrote:


The idea of using belts, and gearboxes, and rack and pinions, sounds like a
bad recipe.

While I did suggest a bar across the gantry, the problem is that you're
carrying all those gears, and the motor.
I drew a quick concept sketch of how I would do it. Buy cut-to-length belt,
probably HTD M5  x  30mm wide for your application.

I think this would be quite adequate for a wood router. At the far end of
the table, connect the two idler pulleys with a shaft too. Obviously all
the pulleys and motors will be below the table height.

And;
- motor is no longer on the gantry
- no skew can happen
- easy to get your drive ratio
- single motor

http://imgbox.com/ccZJF5nH



On Thu, 4 Oct 2018 at 17:41, Leonardo Marsaglia 
wrote:


Hello Les,

No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
some pictures of the design I'm working on. (The adjustable stands for
levelling are not in the assembly because I'm saving resources on this
laptop)

I like the idea of using the rectangular ways but unfortunately they are
quite expensive for this project and also there's the aligning problem.
With the setup I'm trying to do I can adjust the parallelism on every
corner of the machine and also individually adjust every suport to level
the guides perfectly. I'm sending pictures of everything to clarify what
I'm intending to do. Please note this is under development and some

things

are going to change a little bit.

The idea of welding the frame is out of discussion because I plan to move
and set up this thing in place. Also, I don't have the means to

guarantee a

clean and squared welding for the frame. Instead I decided to do what you
can see in the pictures, having an enormous amount of bolts to keep the
parts rigid and firm.

No problem about using tubing to lower the inertia. I also thought about
reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
and then increase the size of the pinions to have the linear speed I

want.

This way the long shaft doesn't have to withstand the high RPMs.

I uploaded the pictures because the list doesn't allow me to attach them.
Here's the link:

https://imgur.com/a/7kLUWsq


___
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https://lists.sourceforge.net/lists/listinfo/emc-users






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Re: [Emc-users] Yet another topic about gantry homing

[andy pugh]

On Thu, 4 Oct 2018 at 19:45, Leonardo Marsaglia  wrote:

> I would love to have ballscrews but I thought I would need to large of a
> diameter to avoid them to whip. Remember that I have a 3.8 meters in lenght

Have a look at the Bell Everman "Servobelt" concept.

I believe it uses standard metric "T5" belting.


Going back to your homing question: The limit switches shouldn't need
to be _that_ accurate. as long as both servos end up within 180
degrees of the correct encoder index.
Final absolute squaring is then tweaked in the INI file.

I would suggest setting the system up with the beam loose and free to
move first, just enough to hold the uprights upright.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916


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Re: [Emc-users] Yet another topic about gantry homing

[Gene Heskett]

On Thursday 04 October 2018 15:28:52 Ken Strauss wrote:

> I haven't been following this thread so I apologize if this was
> previously noted.
>
> One possible solution to the ball screw whip issue is to spin the
> ballnut rather than the ballscrew. In this scheme the ballscrew does
> not rotate and if you tension the screw you should be able to use a
> much smaller diameter screw.
>
This is what I did for the Z drive on the toy HF mill. Rotated the head 
housing 90 degrees to allow access to the front of the post part of the 
slider casting, and made a nut carrier extension on the post, putting 
the motor above the top of the post with a timing belt drive to the nut. 
Carrying 2 bronze nuts on a 1/2" acme bolt fixed into the slider, so the 
backlash can be adjusted, backlash has stayed below 3 thou for several 
years now.  And with the same driver as the xy axis uses to drive those 
ball screws directly, Z is still about 3x faster than xy.

> > -Original Message-
> > From: Leonardo Marsaglia [mailto:ldmarsag...@gmail.com]
> > Sent: Thursday, October 04, 2018 2:42 PM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Yet another topic about gantry homing
> >
> > Hello Chris,
> >
> > I would love to have ballscrews but I thought I would need to large
> > of a diameter to avoid them to whip. Remember that I have a 3.8
> > meters in lenght for the longest joint. I've reading about using
> > anti whip guides that move with the gantry and also aply tension in
> > the screw with a nut to improve the work speed and reduce whip but I
> > don't know wich option is better. Also there's the solution of
> > rotating the nut.
> >
> > Anyway, for such long ways and screws, I need to see if I don't have
> > too much trouble importing them to my country, because of the size
> > of the package. I'll just have to make a call to DHL here in
> > Argentina!
> >
> > Thank you!
> >
> > El jue., 4 oct. 2018 a las 14:58, Chris Albertson (<
> >
> > albertson.ch...@gmail.com>) escribi�:
> > > On Thu, Oct 4, 2018 at 5:49 AM Leonardo Marsaglia
> >
> > 
> >
> > > wrote:
> > > > About the last question. Is there any disadvantage other than
> > > > may be a little more mechanical complexity with the one motor
> > > > and shaft
> >
> > approach?
> >
> > > > Because I've seen lots of routers driven with two motors that I
> > > > almost think it's mandatory for some reason.
> > >
> > > What are the guide rails made of?  precision stainless steel or
> > > chromed? They will need to be very high quality and very expensing
> > > if you use a bronze bushing.I think most people are going with
> > > HDPE.  The friction is lower and you never need to use lube.  that
> > > last part mean the rails are
> > > never coat "dust magnets"You can buy HDPE bearing for not much
> >
> > money.
> >
> > > Typically there bearing are not very thick and are pressed into
> > > aluminum housing
> > >
> > > Also they make rails that lay on the table like rail road tracks
> > > the seem like a good way to go and then use round rails in the
> > > second axis. or use these for both.They are inexpensive and
> > > you can mount them to
> >
> > aluminum
> >
> > > extrusions of  any size.   these would be absolutely rigid and
> > > you'd not have to make anything. Like save money too as they
> > > don't cost a lot.
> > >
> > > Here is a smaller set, they make them bigger needed
> > > .ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-Linear-Rail
> > > <
> > > https://www.ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-
> >
> > Linear-Rail-Shaft-4-Pcs-SBR12UU-
> > Blocks/202160641942?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%
> > 3D1%26asc%3D52885%26meid%3Db5963b764d384f598e468b383f921b1c%26
> > pid%3D15%26rk%3D4%26rkt%3D12%26sd%3D401470856046%26itm%3D
> > 202160641942&_trksid=p2047675.c15.m1851
> >
> > > I know someone who built a large router and, all I can say is the
> > > quality of the rails REALY matters.  That is where all the budget
> > > needs to go. The supported ones are nice because you can place
> > > shim shock under them and use a laser to get perfect alignment.
> > >
> > > About rack and pinion.   You will need way-expensive rack and
> > > pinion set to
> > > reduce backlash.  Butter to use a timing belt (with curves tooth
> >

Re: [Emc-users] Yet another topic about gantry homing

[Gregg Eshelman via Emc-users]

https://www.youtube.com/watch?v=vETkf1sqo3M=220s



   On Thursday, October 4, 2018, 3:41:58 PM MDT, Gregg Eshelman via Emc-users 
 wrote:  
 
 Here's a way to drive the gantry with roller chains. Using fewer changes of 
drive is always better since going from a shaft, to worm gear, to rack and 
pinion has more places for backlash. The same mechanism as in this video can be 
used with lengths of toothed belt.
 
Roller chain drive Plasma table - YouTube

| 
| 
| 
|  |  |

 |

 |
| 
|  | 
Roller chain drive Plasma table - YouTube

  
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Re: [Emc-users] Yet another topic about gantry homing

[Gregg Eshelman via Emc-users]

Here's a way to drive the gantry with roller chains. Using fewer changes of 
drive is always better since going from a shaft, to worm gear, to rack and 
pinion has more places for backlash. The same mechanism as in this video can be 
used with lengths of toothed belt.
 
Roller chain drive Plasma table - YouTube

| 
| 
| 
|  |  |

 |

 |
| 
|  | 
Roller chain drive Plasma table - YouTube


 |

 |

 |




On Thursday, October 4, 2018, 6:50:45 AM MDT, Leonardo Marsaglia 
 wrote:  

About how to drive and home the gantry. From what we've been talking and
thinking it through a little more, I'm thinking that the best solution is
the one Gregg suggested. To have a transversal shaft on the gantry driven
by the servo motor by a worm and gear reduction with the timing pulleys on
each end of the shaft driving the pinions. This way I can adjust and square
the two columns and it should stay squared at any time. This is really
important because this is going to be used by a regular operator, so this
has to be as reliable and fail proof as possible.  
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Re: [Emc-users] Yet another topic about gantry homing

[Todd Zuercher]

For a CNC router used primarily for wood and some aluminum I would not consider 
anything other than a profile linear bearing such as these for the ways. 
https://www.ebay.com/itm/2-sets-HGR25-2000mm-Hiwin-Liner-rail-4-pcs-HGH25CA-Block-Bearing/142629148212?hash=item21355c1634:g:AP0AAOSwfGdbRtAw

I don’t think 1kw is over kill for a wood router especially if you are only 
using one to move the gantry.  Wood routers need to move pretty fast, and 
having too low acceleration can be a big problem.

Also don’t skimp on the spindle, 5kw minimum and 8-12kw is nice.  (Unless your 
just building a light duty wood carver, which it doesn't sound like you are.)

Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street 
Dalton, Ohio 44618
Phone:  (330)828-2105ext. 2031

-Original Message-
From: Leonardo Marsaglia  
Sent: Thursday, October 04, 2018 8:47 AM
To: Enhanced Machine Controller (EMC) 
Subject: Re: [Emc-users] Yet another topic about gantry homing

First of all, thank you guys for your advices as always!

I'm gonna try an asnwer this on one message because sadly gmail doesn't have 
the quote selected text feature anymore.

About the oversized motors. Yes, I also think that for a normal router 1 kw per 
side is too much. But the thing is, I'm planning to use round guides with 
bronze adjustable bearings. I decided this because I want more rigidity for an 
eventual need of machining aluminum, and also because I think this kind of 
guides with whipers are much more reliable than the recirculating ball ones. 
Also, I don't think I can have the adjustable feature with the slotted ball 
bearings. I'm attaching a picture of the bearing I plan to make, there are no 
lube channels on the model but they will be on the final part.

So, to sum up, with these kind of bearings I expect more resistance on the 
joints, and also the router is 2 meters x 3,8 meters long so to have enough 
rigidity I'm planning to use steel and cast iron, so that's why I'm oversizing 
the motors. Besides, there's no much difference between a 400W and a 1Kw  
chinese servo motor and drive on ebay.

About how to drive and home the gantry. From what we've been talking and 
thinking it through a little more, I'm thinking that the best solution is the 
one Gregg suggested. To have a transversal shaft on the gantry driven by the 
servo motor by a worm and gear reduction with the timing pulleys on each end of 
the shaft driving the pinions. This way I can adjust and square the two columns 
and it should stay squared at any time. This is really important because this 
is going to be used by a regular operator, so this has to be as reliable and 
fail proof as possible.

About the last question. Is there any disadvantage other than may be a little 
more mechanical complexity with the one motor and shaft approach?
Because I've seen lots of routers driven with two motors that I almost think 
it's mandatory for some reason.

Thanks again!

Leonardo








El jue., 4 oct. 2018 a las 0:03, Gregg Eshelman via Emc-users (<
emc-users@lists.sourceforge.net>) escribió:

>  The easiest method is mechanically connect the two sides with a shaft 
> along the gantry and use one motor. Then it *cannot rack* or have any 
> of the other issues that can happen with driving both sides of a 
> constrained axis with two motors.
> If you need more Z height, you can elevate the racks on the sides. Or 
> run chains or belts from the cross shaft ends down to stub shafts with 
> the pinion gears.
>
> On Wednesday, October 3, 2018, 4:03:48 AM MDT, Leonardo Marsaglia 
> < ldmarsag...@gmail.com> wrote:
>
>  Hello to all!
> 
>
> About how to drive both Y joints as one axis: I've read that there's a 
> way of simply adding two Y joints for the Y axis in the 2.8 master 
> branch but I don't know if there's documentation available already.
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>

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Re: [Emc-users] Yet another topic about gantry homing

[Todd Zuercher]

Ball screws can be had that long, but they aren't cheap and you're in rotating 
nut only territory.

I've bought custom length screws directly from Hiwin for reasonable amounts of 
money (a C7 rolled screw and nut cost about half what the machine's OE charges 
for a replacement lead screw and so far it has lasted more than 3x as long.)
https://motioncontrolsystems.hiwin.com/configurator/ballscrews-main-configurator


Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street 
Dalton, Ohio 44618
Phone:  (330)828-2105ext. 2031

-Original Message-
From: Roland Jollivet  
Sent: Thursday, October 04, 2018 3:46 PM
To: Enhanced Machine Controller (EMC) 
Subject: [Emc-users] Yet another topic about gantry homing

The OP said the table is 3.8m long


On Thu, 4 Oct 2018 at 21:35, Chris Albertson 
wrote:

> Have you seen the new style ball screws?   They are now cheaper then belts
> and have pretty "over kill" specs.
>
> The problem with a 30mm wide belt drive is the need to resist  the belt
> tension and a way to adjust it.   Not only the tension between the two
> pulleys but there is side load on the motor shaft unless you use a flexible
> coupler and ball bearings on both sides of the drive pulley.  The lead
> screw is mechanically simpler because the motor can be directly 
> coupled to the screw and for $70 you get all the end blocks and mounting 
> hardware.
> These have made router design nearly a "screw driver only" project.  No
> design to even much thinking needed.   I bought one for the vertical axis
> of a CNC milling machine and I can set there is zero backlash and not 
> adjust needed or the life of the machine.  Cost me about $35.
>
> A screw give the drive motor a larger mechanical deduction and you can 
> likely skip the need for a reduction stage.  A screw might advance the 
> axis 4mm per revolution but a belt drive moves maybe 30 to 36mm per rev.
>  You get more force the resolution with a 4mm pitch ball screw.
>
> You can make a one meter square X,Y router base or laser cutter today 
> using two pair of supported rails and two screws for under $250 plus 
> the motors and your z-axis.
>
> On Thu, Oct 4, 2018 at 11:41 AM Roland Jollivet 
>  >
> wrote:
>
> > The idea of using belts, and gearboxes, and rack and pinions, sounds
> like a
> > bad recipe.
> >
> > While I did suggest a bar across the gantry, the problem is that 
> > you're carrying all those gears, and the motor.
> > I drew a quick concept sketch of how I would do it. Buy 
> > cut-to-length
> belt,
> > probably HTD M5  x  30mm wide for your application.
> >
> > I think this would be quite adequate for a wood router. At the far 
> > end of the table, connect the two idler pulleys with a shaft too. 
> > Obviously all the pulleys and motors will be below the table height.
> >
> > And;
> > - motor is no longer on the gantry
> > - no skew can happen
> > - easy to get your drive ratio
> > - single motor
> >
> > http://imgbox.com/ccZJF5nH
> >
> >
> >
> > On Thu, 4 Oct 2018 at 17:41, Leonardo Marsaglia 
> > 
> > wrote:
> >
> > > Hello Les,
> > >
> > > No, I plan to support 50 mm bars every 600 mm more or less. I'm
> attaching
> > > some pictures of the design I'm working on. (The adjustable stands 
> > > for levelling are not in the assembly because I'm saving resources 
> > > on this
> > > laptop)
> > >
> > > I like the idea of using the rectangular ways but unfortunately 
> > > they
> are
> > > quite expensive for this project and also there's the aligning problem.
> > > With the setup I'm trying to do I can adjust the parallelism on 
> > > every corner of the machine and also individually adjust every 
> > > suport to
> level
> > > the guides perfectly. I'm sending pictures of everything to 
> > > clarify
> what
> > > I'm intending to do. Please note this is under development and 
> > > some
> > things
> > > are going to change a little bit.
> > >
> > > The idea of welding the frame is out of discussion because I plan 
> > > to
> move
> > > and set up this thing in place. Also, I don't have the means to
> > guarantee a
> > > clean and squared welding for the frame. Instead I decided to do 
> > > what
> you
> > > can see in the pictures, having an enormous amount of bolts to 
> > > keep the parts rigid and firm.
> > >
> > > No problem about using tubing to lower the inertia. I also thought
> about
> > > reducing the 3000 max RPM with the worm and gear to 100 RPM on the
> shaft
> > > and then increase the size of the pinions to have the linear speed 
> > > I
> > want.
> > > This way the long shaft doesn't have to withstand the high RPMs.
> > >
> > > I uploaded the pictures because the list doesn't allow me to 
> > > attach
> them.
> > > Here's the link:
> > >
> > > https://imgur.com/a/7kLUWsq
> > >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
>
> 

Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

On Thu, Oct 4, 2018 at 12:48 PM Roland Jollivet 
wrote:

> The OP said the table is 3.8m long
>

Yes, a screw is better suited to something about 1.5 meters of under.
Likely best to use a pair of belts, one each side.

How much does a belt tension change with temperature?  Normally it is a
non-issue but this is one very long belt.

-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

On Thu, Oct 4, 2018 at 12:29 PM Ken Strauss  wrote:

>
> One possible solution to the ball screw whip issue is to spin the ballnut
> rather than the ballscrew. In this scheme the ballscrew does not rotate
> and if
> you tension the screw you should be able to use a much smaller diameter
> screw.
>
>
Yes, this is how my milling machines designed the screw remains
stationary.  The nut is embedded in a timing belt and spins.

For a large long 4 meter router you might need a belt drive but  if there
is a shorter axis the screw could work.  Screws go up to about 1.5 meters
in length

What I found from others is that the quality of the rails and bearing is
really what matters.   Much as we lie to focus on the motors and rive, it
is the rails that define the machine.
-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

Have you seen the new style ball screws?   They are now cheaper then belts
and have pretty "over kill" specs.

The problem with a 30mm wide belt drive is the need to resist  the belt
tension and a way to adjust it.   Not only the tension between the two
pulleys but there is side load on the motor shaft unless you use a flexible
coupler and ball bearings on both sides of the drive pulley.  The lead
screw is mechanically simpler because the motor can be directly coupled to
the screw and for $70 you get all the end blocks and mounting hardware.
These have made router design nearly a "screw driver only" project.  No
design to even much thinking needed.   I bought one for the vertical axis
of a CNC milling machine and I can set there is zero backlash and not
adjust needed or the life of the machine.  Cost me about $35.

A screw give the drive motor a larger mechanical deduction and you can
likely skip the need for a reduction stage.  A screw might advance the axis
4mm per revolution but a belt drive moves maybe 30 to 36mm per rev.
 You get more force the resolution with a 4mm pitch ball screw.

You can make a one meter square X,Y router base or laser cutter today using
two pair of supported rails and two screws for under $250 plus the motors
and your z-axis.

On Thu, Oct 4, 2018 at 11:41 AM Roland Jollivet 
wrote:

> The idea of using belts, and gearboxes, and rack and pinions, sounds like a
> bad recipe.
>
> While I did suggest a bar across the gantry, the problem is that you're
> carrying all those gears, and the motor.
> I drew a quick concept sketch of how I would do it. Buy cut-to-length belt,
> probably HTD M5  x  30mm wide for your application.
>
> I think this would be quite adequate for a wood router. At the far end of
> the table, connect the two idler pulleys with a shaft too. Obviously all
> the pulleys and motors will be below the table height.
>
> And;
> - motor is no longer on the gantry
> - no skew can happen
> - easy to get your drive ratio
> - single motor
>
> http://imgbox.com/ccZJF5nH
>
>
>
> On Thu, 4 Oct 2018 at 17:41, Leonardo Marsaglia 
> wrote:
>
> > Hello Les,
> >
> > No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
> > some pictures of the design I'm working on. (The adjustable stands for
> > levelling are not in the assembly because I'm saving resources on this
> > laptop)
> >
> > I like the idea of using the rectangular ways but unfortunately they are
> > quite expensive for this project and also there's the aligning problem.
> > With the setup I'm trying to do I can adjust the parallelism on every
> > corner of the machine and also individually adjust every suport to level
> > the guides perfectly. I'm sending pictures of everything to clarify what
> > I'm intending to do. Please note this is under development and some
> things
> > are going to change a little bit.
> >
> > The idea of welding the frame is out of discussion because I plan to move
> > and set up this thing in place. Also, I don't have the means to
> guarantee a
> > clean and squared welding for the frame. Instead I decided to do what you
> > can see in the pictures, having an enormous amount of bolts to keep the
> > parts rigid and firm.
> >
> > No problem about using tubing to lower the inertia. I also thought about
> > reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
> > and then increase the size of the pinions to have the linear speed I
> want.
> > This way the long shaft doesn't have to withstand the high RPMs.
> >
> > I uploaded the pictures because the list doesn't allow me to attach them.
> > Here's the link:
> >
> > https://imgur.com/a/7kLUWsq
> >
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Yet another topic about gantry homing

[Ken Strauss]

I haven't been following this thread so I apologize if this was previously 
noted.

One possible solution to the ball screw whip issue is to spin the ballnut 
rather than the ballscrew. In this scheme the ballscrew does not rotate and if 
you tension the screw you should be able to use a much smaller diameter screw.

> -Original Message-
> From: Leonardo Marsaglia [mailto:ldmarsag...@gmail.com]
> Sent: Thursday, October 04, 2018 2:42 PM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Yet another topic about gantry homing
>
> Hello Chris,
>
> I would love to have ballscrews but I thought I would need to large of a
> diameter to avoid them to whip. Remember that I have a 3.8 meters in lenght
> for the longest joint. I've reading about using anti whip guides that move
> with the gantry and also aply tension in the screw with a nut to improve
> the work speed and reduce whip but I don't know wich option is better. Also
> there's the solution of rotating the nut.
>
> Anyway, for such long ways and screws, I need to see if I don't have too
> much trouble importing them to my country, because of the size of the
> package. I'll just have to make a call to DHL here in Argentina!
>
> Thank you!
>
> El jue., 4 oct. 2018 a las 14:58, Chris Albertson (<
> albertson.ch...@gmail.com>) escribió:
>
> > On Thu, Oct 4, 2018 at 5:49 AM Leonardo Marsaglia
> 
> > wrote:
> >
> > >
> > >
> > > About the last question. Is there any disadvantage other than may be a
> > > little more mechanical complexity with the one motor and shaft
> approach?
> > > Because I've seen lots of routers driven with two motors that I almost
> > > think it's mandatory for some reason.
> > >
> >
> > What are the guide rails made of?  precision stainless steel or chromed?
> > They will need to be very high quality and very expensing if you use a
> > bronze bushing.I think most people are going with HDPE.  The friction
> > is lower and you never need to use lube.  that last part mean the rails 
> > are
> > never coat "dust magnets"You can buy HDPE bearing for not much
> money.
> > Typically there bearing are not very thick and are pressed into aluminum
> > housing
> >
> > Also they make rails that lay on the table like rail road tracks the seem
> > like a good way to go and then use round rails in the second axis. or use
> > these for both.They are inexpensive and you can mount them to
> aluminum
> > extrusions of  any size.   these would be absolutely rigid and you'd not
> > have to make anything. Like save money too as they don't cost a lot.
> >
> > Here is a smaller set, they make them bigger needed
> > .ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-Linear-Rail
> > <
> > https://www.ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-
> Linear-Rail-Shaft-4-Pcs-SBR12UU-
> Blocks/202160641942?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%
> 3D1%26asc%3D52885%26meid%3Db5963b764d384f598e468b383f921b1c%26
> pid%3D15%26rk%3D4%26rkt%3D12%26sd%3D401470856046%26itm%3D
> 202160641942&_trksid=p2047675.c15.m1851
> > >
> >
> > I know someone who built a large router and, all I can say is the quality
> > of the rails REALY matters.  That is where all the budget needs to go.
> >  The supported ones are nice because you can place shim shock under them
> > and use a laser to get perfect alignment.
> >
> > About rack and pinion.   You will need way-expensive rack and pinion set 
> > to
> > reduce backlash.  Butter to use a timing belt (with curves tooth profile)
> > as these have zero backlash and cost less.   The other option is ball
> > screws.   Ball screws will out perform racks and cost a lot less and
> > again bell screws are zero backlash
> >
> > User direct drive or timing belt reduction as gear reductions on the 
> > motors
> > have backlash.
> >
> > It is assign how much the cost of zero backlash ball drives have fallen.
> > They are now the lowest cost option for precision linear drive.These
> > are made  mostly for the Chinese domestic market but some are sold on
> eBay
> >The Chinese domestic market is HUGE compared to Europe or USA and we
> can
> > take advantage of their economy of scale.
> > For usr use a 12mm diameter screw would work well.   Use them at least of
> > the shorter axis (certainly the  axis) here is an example.  I have a set 
> > of
> > these.  The bearing are hold in compression so there is zero backlash and
> > they measure "perfect" at least according to a dial 

Re: [Emc-users] Yet another topic about gantry homing

[Leonardo Marsaglia]

Hello Chris,

I would love to have ballscrews but I thought I would need to large of a
diameter to avoid them to whip. Remember that I have a 3.8 meters in lenght
for the longest joint. I've reading about using anti whip guides that move
with the gantry and also aply tension in the screw with a nut to improve
the work speed and reduce whip but I don't know wich option is better. Also
there's the solution of rotating the nut.

Anyway, for such long ways and screws, I need to see if I don't have too
much trouble importing them to my country, because of the size of the
package. I'll just have to make a call to DHL here in Argentina!

Thank you!

El jue., 4 oct. 2018 a las 14:58, Chris Albertson (<
albertson.ch...@gmail.com>) escribió:

> On Thu, Oct 4, 2018 at 5:49 AM Leonardo Marsaglia 
> wrote:
>
> >
> >
> > About the last question. Is there any disadvantage other than may be a
> > little more mechanical complexity with the one motor and shaft approach?
> > Because I've seen lots of routers driven with two motors that I almost
> > think it's mandatory for some reason.
> >
>
> What are the guide rails made of?  precision stainless steel or chromed?
> They will need to be very high quality and very expensing if you use a
> bronze bushing.I think most people are going with HDPE.  The friction
> is lower and you never need to use lube.  that last part mean the rails are
> never coat "dust magnets"You can buy HDPE bearing for not much money.
> Typically there bearing are not very thick and are pressed into aluminum
> housing
>
> Also they make rails that lay on the table like rail road tracks the seem
> like a good way to go and then use round rails in the second axis. or use
> these for both.They are inexpensive and you can mount them to aluminum
> extrusions of  any size.   these would be absolutely rigid and you'd not
> have to make anything. Like save money too as they don't cost a lot.
>
> Here is a smaller set, they make them bigger needed
> .ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-Linear-Rail
> <
> https://www.ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-Linear-Rail-Shaft-4-Pcs-SBR12UU-Blocks/202160641942?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D52885%26meid%3Db5963b764d384f598e468b383f921b1c%26pid%3D15%26rk%3D4%26rkt%3D12%26sd%3D401470856046%26itm%3D202160641942&_trksid=p2047675.c15.m1851
> >
>
> I know someone who built a large router and, all I can say is the quality
> of the rails REALY matters.  That is where all the budget needs to go.
>  The supported ones are nice because you can place shim shock under them
> and use a laser to get perfect alignment.
>
> About rack and pinion.   You will need way-expensive rack and pinion set to
> reduce backlash.  Butter to use a timing belt (with curves tooth profile)
> as these have zero backlash and cost less.   The other option is ball
> screws.   Ball screws will out perform racks and cost a lot less and
> again bell screws are zero backlash
>
> User direct drive or timing belt reduction as gear reductions on the motors
> have backlash.
>
> It is assign how much the cost of zero backlash ball drives have fallen.
> They are now the lowest cost option for precision linear drive.These
> are made  mostly for the Chinese domestic market but some are sold on eBay
>The Chinese domestic market is HUGE compared to Europe or USA and we can
> take advantage of their economy of scale.
> For usr use a 12mm diameter screw would work well.   Use them at least of
> the shorter axis (certainly the  axis) here is an example.  I have a set of
> these.  The bearing are hold in compression so there is zero backlash and
> they measure "perfect" at least according to a dial indictor.
>
> With these ball screws nd a pair of the rial mounted guedes you can mill
> mild steel and certainly aluminum and have resolution at better them 0.001
> inch.  Use normal stepper motor as the systems nearly frictionless.   Cost
> is very low. Maybe $200 per axis plus the motor for a one meter square
> router.   It is almost disappointing to use this as there is"nothing to
> build"Just some mounting brackets and you are done.
>
> ebay.com/itm/CNC-Ball-Screw-12mm-SFU1204-w-Ballnut-
> <
> https://www.ebay.com/itm/CNC-Ball-Screw-12mm-SFU1204-w-Ballnut-BF-BK10-End-Support-L-250mm-1500mm/173060231282?hash=item284b319072:m:mg4uq51qVvrK8RmcksDoOUg
> >
>
>
>
> >
> > Thanks again!
> >
> > Leonardo
> >
> >
> >
> >
> >
> >
> >
> >
> > El jue., 4 oct. 2018 a las 0:03, Gregg Eshelman via Emc-users (<
> > emc-users@lists.sourceforge.net>) escribió:
> >
> > >  The easiest method is mechanically connect the two sides with a shaft
> > > along the gantry and use one motor. Then it *cannot rack* or have any
> of
> > > the other issues that can happen with driving both sides of a
> constrained
> > > axis with two motors.
> > > If you need more Z height, you can elevate the racks on the sides. Or
> run
> > > chains or belts from the cross shaft 

Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

On Thu, Oct 4, 2018 at 5:49 AM Leonardo Marsaglia 
wrote:

>
>
> About the last question. Is there any disadvantage other than may be a
> little more mechanical complexity with the one motor and shaft approach?
> Because I've seen lots of routers driven with two motors that I almost
> think it's mandatory for some reason.
>

What are the guide rails made of?  precision stainless steel or chromed?
They will need to be very high quality and very expensing if you use a
bronze bushing.I think most people are going with HDPE.  The friction
is lower and you never need to use lube.  that last part mean the rails are
never coat "dust magnets"You can buy HDPE bearing for not much money.
Typically there bearing are not very thick and are pressed into aluminum
housing

Also they make rails that lay on the table like rail road tracks the seem
like a good way to go and then use round rails in the second axis. or use
these for both.They are inexpensive and you can mount them to aluminum
extrusions of  any size.   these would be absolutely rigid and you'd not
have to make anything. Like save money too as they don't cost a lot.

Here is a smaller set, they make them bigger needed
.ebay.com/itm/2-X-SBR12-1000mm-For-CNC-12MM-Supported-Linear-Rail


I know someone who built a large router and, all I can say is the quality
of the rails REALY matters.  That is where all the budget needs to go.
 The supported ones are nice because you can place shim shock under them
and use a laser to get perfect alignment.

About rack and pinion.   You will need way-expensive rack and pinion set to
reduce backlash.  Butter to use a timing belt (with curves tooth profile)
as these have zero backlash and cost less.   The other option is ball
screws.   Ball screws will out perform racks and cost a lot less and
again bell screws are zero backlash

User direct drive or timing belt reduction as gear reductions on the motors
have backlash.

It is assign how much the cost of zero backlash ball drives have fallen.
They are now the lowest cost option for precision linear drive.These
are made  mostly for the Chinese domestic market but some are sold on eBay
   The Chinese domestic market is HUGE compared to Europe or USA and we can
take advantage of their economy of scale.
For usr use a 12mm diameter screw would work well.   Use them at least of
the shorter axis (certainly the  axis) here is an example.  I have a set of
these.  The bearing are hold in compression so there is zero backlash and
they measure "perfect" at least according to a dial indictor.

With these ball screws nd a pair of the rial mounted guedes you can mill
mild steel and certainly aluminum and have resolution at better them 0.001
inch.  Use normal stepper motor as the systems nearly frictionless.   Cost
is very low. Maybe $200 per axis plus the motor for a one meter square
router.   It is almost disappointing to use this as there is"nothing to
build"Just some mounting brackets and you are done.

ebay.com/itm/CNC-Ball-Screw-12mm-SFU1204-w-Ballnut-




>
> Thanks again!
>
> Leonardo
>
>
>
>
>
>
>
>
> El jue., 4 oct. 2018 a las 0:03, Gregg Eshelman via Emc-users (<
> emc-users@lists.sourceforge.net>) escribió:
>
> >  The easiest method is mechanically connect the two sides with a shaft
> > along the gantry and use one motor. Then it *cannot rack* or have any of
> > the other issues that can happen with driving both sides of a constrained
> > axis with two motors.
> > If you need more Z height, you can elevate the racks on the sides. Or run
> > chains or belts from the cross shaft ends down to stub shafts with the
> > pinion gears.
> >
> > On Wednesday, October 3, 2018, 4:03:48 AM MDT, Leonardo Marsaglia <
> > ldmarsag...@gmail.com> wrote:
> >
> >  Hello to all!
> > 
> >
> > About how to drive both Y joints as one axis: I've read that there's a
> way
> > of simply adding two Y joints for the Y axis in the 2.8 master branch
> but I
> > don't know if there's documentation available already.
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

___
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Re: [Emc-users] Yet another topic about gantry homing

[Leonardo Marsaglia]

Well I've been reading the 2.8 Master branch manual about homing and how to
configure two joints for one axis and I think I understand but since I
don't have a Linux PC here to try it out I would like to clarify something.

In the two motors for one axis gantry configuration, does LinuxCNC export
home switch pins for each joint? Or does it export the pins for each axis?

Because the best solution I came out with to have a precise homing without
rocking (and I think is doable) is to have one homeswitch per joint with a
robust mechanism to manually adjust them as precise as possible. And then
use absolute encoders on the pinions to achieve the maximum accuracy level.
This way I can guarantee that if there is some difference from time to time
when hitting the home switches, that won't be a problem since the absolute
enconders keep the exact angular position of the pinion. Am I right on
this? Or is this just a redundancy?

Sorry for the long questions but I've never really worked with this kind of
setup, and I'm used to have both the switch and some encoder reference to
make the homing.

Thank you!

El jue., 4 oct. 2018 a las 12:39, Leonardo Marsaglia ()
escribió:

> Hello Les,
>
> No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
> some pictures of the design I'm working on. (The adjustable stands for
> levelling are not in the assembly because I'm saving resources on this
> laptop)
>
> I like the idea of using the rectangular ways but unfortunately they are
> quite expensive for this project and also there's the aligning problem.
> With the setup I'm trying to do I can adjust the parallelism on every
> corner of the machine and also individually adjust every suport to level
> the guides perfectly. I'm sending pictures of everything to clarify what
> I'm intending to do. Please note this is under development and some things
> are going to change a little bit.
>
> The idea of welding the frame is out of discussion because I plan to move
> and set up this thing in place. Also, I don't have the means to guarantee a
> clean and squared welding for the frame. Instead I decided to do what you
> can see in the pictures, having an enormous amount of bolts to keep the
> parts rigid and firm.
>
> No problem about using tubing to lower the inertia. I also thought about
> reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
> and then increase the size of the pinions to have the linear speed I want.
> This way the long shaft doesn't have to withstand the high RPMs.
>
> I uploaded the pictures because the list doesn't allow me to attach them.
> Here's the link:
>
> https://imgur.com/a/7kLUWsq
>
>
>
> El jue., 4 oct. 2018 a las 12:13, Leonardo Marsaglia (<
> ldmarsag...@gmail.com>) escribió:
>
>> Hello Dave,
>>
>> Well, to avoid the backlash is that or may be using timing belts and
>> pulleys to drive the shaft too. The gearbox is a good idea but I think that
>> can raise the cost too much. Anyway I'll give it a look because I don't
>> want to discard any option.
>>
>> In any case I'm still not sure about wheter use two motors or one motor
>> with a shaft. The latter option makes me feel more secure because it can't
>> go out of squaress easily, unless you have loose belt or something breaks.
>>
>>  By the way I just re send another message that was rejected by the list
>> because of the size of the pictures, I don't know if now you can see it.
>>
>>
>>
>> El jue., 4 oct. 2018 a las 12:04, Leonardo Marsaglia (<
>> ldmarsag...@gmail.com>) escribió:
>>
>>> Hello Les,
>>>
>>> No, I plan to support 50 mm bars every 600 mm more or less. I'm
>>> attaching some pictures of the design I'm working on. (The adjustable
>>> stands for levelling are not in the assembly because I'm saving resources
>>> on this laptop)
>>>
>>> I like the idea of using the rectangular ways but unfortunately they are
>>> quite expensive for this project and also there's the aligning problem.
>>> With the setup I'm trying to do I can adjust the parallelism on every
>>> corner of the machine and also individually adjust every suport to level
>>> the guides perfectly. I'm sending pictures of everything to clarify what
>>> I'm intending to do. Please note this is under development and some things
>>> are going to change a little bit.
>>>
>>> The idea of welding the frame is out of discussion because I plan to
>>> move and set up this thing in place. Also, I don't have the means to
>>> guarantee a clean and squared welding for the frame. Instead I decided to
>>> do what you can see in the pictures, having an enormous amount of bolts to
>>> keep the parts rigid and firm.
>>>
>>> No problem about using tubing to lower the inertia. I also thought about
>>> reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
>>> and then increase the size of the pinions to have the linear speed I want.
>>> This way the long shaft doesn't have to withstand the high RPMs.
>>>
>>> (Second attempt to attach the pictures)

Re: [Emc-users] Yet another topic about gantry homing

[Leonardo Marsaglia]

Hello Les,

No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
some pictures of the design I'm working on. (The adjustable stands for
levelling are not in the assembly because I'm saving resources on this
laptop)

I like the idea of using the rectangular ways but unfortunately they are
quite expensive for this project and also there's the aligning problem.
With the setup I'm trying to do I can adjust the parallelism on every
corner of the machine and also individually adjust every suport to level
the guides perfectly. I'm sending pictures of everything to clarify what
I'm intending to do. Please note this is under development and some things
are going to change a little bit.

The idea of welding the frame is out of discussion because I plan to move
and set up this thing in place. Also, I don't have the means to guarantee a
clean and squared welding for the frame. Instead I decided to do what you
can see in the pictures, having an enormous amount of bolts to keep the
parts rigid and firm.

No problem about using tubing to lower the inertia. I also thought about
reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
and then increase the size of the pinions to have the linear speed I want.
This way the long shaft doesn't have to withstand the high RPMs.

I uploaded the pictures because the list doesn't allow me to attach them.
Here's the link:

https://imgur.com/a/7kLUWsq



El jue., 4 oct. 2018 a las 12:13, Leonardo Marsaglia ()
escribió:

> Hello Dave,
>
> Well, to avoid the backlash is that or may be using timing belts and
> pulleys to drive the shaft too. The gearbox is a good idea but I think that
> can raise the cost too much. Anyway I'll give it a look because I don't
> want to discard any option.
>
> In any case I'm still not sure about wheter use two motors or one motor
> with a shaft. The latter option makes me feel more secure because it can't
> go out of squaress easily, unless you have loose belt or something breaks.
>
>  By the way I just re send another message that was rejected by the list
> because of the size of the pictures, I don't know if now you can see it.
>
>
>
> El jue., 4 oct. 2018 a las 12:04, Leonardo Marsaglia (<
> ldmarsag...@gmail.com>) escribió:
>
>> Hello Les,
>>
>> No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
>> some pictures of the design I'm working on. (The adjustable stands for
>> levelling are not in the assembly because I'm saving resources on this
>> laptop)
>>
>> I like the idea of using the rectangular ways but unfortunately they are
>> quite expensive for this project and also there's the aligning problem.
>> With the setup I'm trying to do I can adjust the parallelism on every
>> corner of the machine and also individually adjust every suport to level
>> the guides perfectly. I'm sending pictures of everything to clarify what
>> I'm intending to do. Please note this is under development and some things
>> are going to change a little bit.
>>
>> The idea of welding the frame is out of discussion because I plan to move
>> and set up this thing in place. Also, I don't have the means to guarantee a
>> clean and squared welding for the frame. Instead I decided to do what you
>> can see in the pictures, having an enormous amount of bolts to keep the
>> parts rigid and firm.
>>
>> No problem about using tubing to lower the inertia. I also thought about
>> reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
>> and then increase the size of the pinions to have the linear speed I want.
>> This way the long shaft doesn't have to withstand the high RPMs.
>>
>> (Second attempt to attach the pictures)
>>
>> El jue., 4 oct. 2018 a las 12:00, Dave Cole ()
>> escribió:
>>
>>> I'd avoid a worm gear drive.   They are prone to wear and backlash.
>>> I'd look for a good deal on a servo grade planetary 10:1 gearbox that
>>> fits your Chinese motor.
>>> Probably the easiest and most rigid drive solution is to use two motors
>>> each with a planetary gear box and direct drive a pinion on a rack.
>>> If you want to mill aluminum and need rigidity, that's the way I would
>>> go.
>>> You might want to weld the frame in sections and then bolt it together.
>>> If you don't have a platen to weld it on, you might want to contract out
>>> part of the frame welding.
>>>
>>> Dave
>>>
>>> On 10/4/2018 10:41 AM, Leonardo Marsaglia wrote:
>>> > By the way, on the pictures there are missing details I didn't draw
>>> yet,
>>> > like setscrews for parallel regulation and things like that. Also, I
>>> have
>>> > yet to modify the design for the one motor and shaft approach and see
>>> wich
>>> > is better.
>>> >
>>> > El jue., 4 oct. 2018 a las 11:37, Leonardo Marsaglia (<
>>> ldmarsag...@gmail.com>)
>>> > escribió:
>>> >
>>> >> Hello Les,
>>> >>
>>> >> No, I plan to support 50 mm bars every 600 mm more or less. I'm
>>> attaching
>>> >> some pictures of the design I'm working on. (The adjustable stands for
>>> >> 

Re: [Emc-users] Yet another topic about gantry homing

[Leonardo Marsaglia]

Hello Dave,

Well, to avoid the backlash is that or may be using timing belts and
pulleys to drive the shaft too. The gearbox is a good idea but I think that
can raise the cost too much. Anyway I'll give it a look because I don't
want to discard any option.

In any case I'm still not sure about wheter use two motors or one motor
with a shaft. The latter option makes me feel more secure because it can't
go out of squaress easily, unless you have loose belt or something breaks.

 By the way I just re send another message that was rejected by the list
because of the size of the pictures, I don't know if now you can see it.



El jue., 4 oct. 2018 a las 12:04, Leonardo Marsaglia ()
escribió:

> Hello Les,
>
> No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
> some pictures of the design I'm working on. (The adjustable stands for
> levelling are not in the assembly because I'm saving resources on this
> laptop)
>
> I like the idea of using the rectangular ways but unfortunately they are
> quite expensive for this project and also there's the aligning problem.
> With the setup I'm trying to do I can adjust the parallelism on every
> corner of the machine and also individually adjust every suport to level
> the guides perfectly. I'm sending pictures of everything to clarify what
> I'm intending to do. Please note this is under development and some things
> are going to change a little bit.
>
> The idea of welding the frame is out of discussion because I plan to move
> and set up this thing in place. Also, I don't have the means to guarantee a
> clean and squared welding for the frame. Instead I decided to do what you
> can see in the pictures, having an enormous amount of bolts to keep the
> parts rigid and firm.
>
> No problem about using tubing to lower the inertia. I also thought about
> reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
> and then increase the size of the pinions to have the linear speed I want.
> This way the long shaft doesn't have to withstand the high RPMs.
>
> (Second attempt to attach the pictures)
>
> El jue., 4 oct. 2018 a las 12:00, Dave Cole ()
> escribió:
>
>> I'd avoid a worm gear drive.   They are prone to wear and backlash.
>> I'd look for a good deal on a servo grade planetary 10:1 gearbox that
>> fits your Chinese motor.
>> Probably the easiest and most rigid drive solution is to use two motors
>> each with a planetary gear box and direct drive a pinion on a rack.
>> If you want to mill aluminum and need rigidity, that's the way I would go.
>> You might want to weld the frame in sections and then bolt it together.
>> If you don't have a platen to weld it on, you might want to contract out
>> part of the frame welding.
>>
>> Dave
>>
>> On 10/4/2018 10:41 AM, Leonardo Marsaglia wrote:
>> > By the way, on the pictures there are missing details I didn't draw yet,
>> > like setscrews for parallel regulation and things like that. Also, I
>> have
>> > yet to modify the design for the one motor and shaft approach and see
>> wich
>> > is better.
>> >
>> > El jue., 4 oct. 2018 a las 11:37, Leonardo Marsaglia (<
>> ldmarsag...@gmail.com>)
>> > escribió:
>> >
>> >> Hello Les,
>> >>
>> >> No, I plan to support 50 mm bars every 600 mm more or less. I'm
>> attaching
>> >> some pictures of the design I'm working on. (The adjustable stands for
>> >> levelling are not in the assembly because I'm saving resources on this
>> >> laptop)
>> >>
>> >> I like the idea of using the rectangular ways but unfortunately they
>> are
>> >> quite expensive for this project and also there's the aligning problem.
>> >> With the setup I'm trying to do I can adjust the parallelism on every
>> >> corner of the machine and also individually adjust every suport to
>> level
>> >> the guides perfectly. I'm sending pictures of everything to clarify
>> what
>> >> I'm intending to do. Please note this is under development and some
>> things
>> >> are going to change a little bit.
>> >>
>> >> The idea of welding the frame is out of discussion because I plan to
>> move
>> >> and set up this thing in place. Also, I don't have the means to
>> guarantee a
>> >> clean and squared welding for the frame. Instead I decided to do what
>> you
>> >> can see in the pictures, having an enormous amount of bolts to keep the
>> >> parts rigid and firm.
>> >>
>> >> No problem about using tubing to lower the inertia. I also thought
>> about
>> >> reducing the 3000 max RPM with the worm and gear to 100 RPM on the
>> shaft
>> >> and then increase the size of the pinions to have the linear speed I
>> want.
>> >> This way the long shaft doesn't have to withstand the high RPMs.
>> >>
>> >> Let me know if you can see the pictures.
>> >>
>> >>
>> >>
>> >> El jue., 4 oct. 2018 a las 10:52, Les Newell (<
>> les.new...@fastmail.co.uk>)
>> >> escribió:
>> >>
>> >>> Using two motors is mechanically simpler and has lower rotational
>> >>> inertia but I am not a fan of this setup. If you use a tube rather

Re: [Emc-users] Yet another topic about gantry homing

[Dave Cole]

I'd avoid a worm gear drive.   They are prone to wear and backlash.
I'd look for a good deal on a servo grade planetary 10:1 gearbox that 
fits your Chinese motor.
Probably the easiest and most rigid drive solution is to use two motors 
each with a planetary gear box and direct drive a pinion on a rack.

If you want to mill aluminum and need rigidity, that's the way I would go.
You might want to weld the frame in sections and then bolt it together.
If you don't have a platen to weld it on, you might want to contract out 
part of the frame welding.


Dave

On 10/4/2018 10:41 AM, Leonardo Marsaglia wrote:

By the way, on the pictures there are missing details I didn't draw yet,
like setscrews for parallel regulation and things like that. Also, I have
yet to modify the design for the one motor and shaft approach and see wich
is better.

El jue., 4 oct. 2018 a las 11:37, Leonardo Marsaglia ()
escribió:


Hello Les,

No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
some pictures of the design I'm working on. (The adjustable stands for
levelling are not in the assembly because I'm saving resources on this
laptop)

I like the idea of using the rectangular ways but unfortunately they are
quite expensive for this project and also there's the aligning problem.
With the setup I'm trying to do I can adjust the parallelism on every
corner of the machine and also individually adjust every suport to level
the guides perfectly. I'm sending pictures of everything to clarify what
I'm intending to do. Please note this is under development and some things
are going to change a little bit.

The idea of welding the frame is out of discussion because I plan to move
and set up this thing in place. Also, I don't have the means to guarantee a
clean and squared welding for the frame. Instead I decided to do what you
can see in the pictures, having an enormous amount of bolts to keep the
parts rigid and firm.

No problem about using tubing to lower the inertia. I also thought about
reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
and then increase the size of the pinions to have the linear speed I want.
This way the long shaft doesn't have to withstand the high RPMs.

Let me know if you can see the pictures.



El jue., 4 oct. 2018 a las 10:52, Les Newell ()
escribió:


Using two motors is mechanically simpler and has lower rotational
inertia but I am not a fan of this setup. If you use a tube rather than
a solid shaft, you won't add a lot of inertia. I'm thinking of building
another plasma cutter and it will probably use a shaft rather than 2
motors.


But the thing is, I'm planning to use round guides
with bronze adjustable bearings.

Do you mean guides that are only supported at the ends? This is a very
bad idea. They'll flex and bounce all over the place. You are also
likely to get a lot of wear unless you pressure feed lubricant. If you
do that oil will go everywhere. My router uses box ways on the Y and Z
axes with oil feed. It gets pretty messy at times.

Most modern commercial routers and many machining centres use
rectangular linear ways, such as this
<
https://www.qualitybearingsonline.com/lwl25r240bhs2-iko-maintenance-free-linear-guide-rail/>.

They are very rigid and lasts a long time with very little wear. The
only disadvantage is that you need to be careful to make sure everything
is perfectly aligned. These have very little give in them. Another
option is supported round rail such as this
<
https://www.amazon.co.uk/TEN-HIGH-Supported-SBR40UU-BlockBearing-Bearing/dp/B01N10JF5N>.

For the sort of size machine you are talking about you'll need at least
40mm round rail. Round rails wear faster than rectangular but are a lot
less fussy about alignment.


So, to sum up, with these kind of bearings I expect more resistance on

the

joints, and also the router is 2 meters x 3,8 meters long so to have

enough

rigidity I'm planning to use steel and cast iron, so that's why I'm
oversizing the motors.

To give you an idea about motor sizing the motors on my router (1 per
axis) are about 1.8kw and it's scary.  My tool changer is mounted on a
bracket made from 50mmx50mm box section. I messed up the tool change
sequencing a while back and it pushed the tool changer out of the way
without breaking a sweat. It tool a lot of effort with big levers to
twist it straight again. Here is a link to a similar machine to mine but
without a tool changer
<
https://www.bidspotter.co.uk/en-gb/auction-catalogues/cjm-asset/catalogue-id-cjm10389/lot-47df49af-bf1a-4676-ab88-a75a00f5f92b>.

Lots of heavy steel and cast iron. Mine originally had 4 drill heads and
2 spindles. If it was easy to dial back the power I would. If something
goes wrong the machine will keep pushing until something breaks.

I do maintenance work on a router with 750W motors. A while back the
spindle stalled while it was cutting. It bent the 1/2" cutter nearly 90
degrees and carried on.

Les

On 04/10/2018 13:47, Leonardo 

Re: [Emc-users] Yet another topic about gantry homing

[Leonardo Marsaglia]

By the way, on the pictures there are missing details I didn't draw yet,
like setscrews for parallel regulation and things like that. Also, I have
yet to modify the design for the one motor and shaft approach and see wich
is better.

El jue., 4 oct. 2018 a las 11:37, Leonardo Marsaglia ()
escribió:

> Hello Les,
>
> No, I plan to support 50 mm bars every 600 mm more or less. I'm attaching
> some pictures of the design I'm working on. (The adjustable stands for
> levelling are not in the assembly because I'm saving resources on this
> laptop)
>
> I like the idea of using the rectangular ways but unfortunately they are
> quite expensive for this project and also there's the aligning problem.
> With the setup I'm trying to do I can adjust the parallelism on every
> corner of the machine and also individually adjust every suport to level
> the guides perfectly. I'm sending pictures of everything to clarify what
> I'm intending to do. Please note this is under development and some things
> are going to change a little bit.
>
> The idea of welding the frame is out of discussion because I plan to move
> and set up this thing in place. Also, I don't have the means to guarantee a
> clean and squared welding for the frame. Instead I decided to do what you
> can see in the pictures, having an enormous amount of bolts to keep the
> parts rigid and firm.
>
> No problem about using tubing to lower the inertia. I also thought about
> reducing the 3000 max RPM with the worm and gear to 100 RPM on the shaft
> and then increase the size of the pinions to have the linear speed I want.
> This way the long shaft doesn't have to withstand the high RPMs.
>
> Let me know if you can see the pictures.
>
>
>
> El jue., 4 oct. 2018 a las 10:52, Les Newell ()
> escribió:
>
>> Using two motors is mechanically simpler and has lower rotational
>> inertia but I am not a fan of this setup. If you use a tube rather than
>> a solid shaft, you won't add a lot of inertia. I'm thinking of building
>> another plasma cutter and it will probably use a shaft rather than 2
>> motors.
>>
>> > But the thing is, I'm planning to use round guides
>> > with bronze adjustable bearings.
>>
>> Do you mean guides that are only supported at the ends? This is a very
>> bad idea. They'll flex and bounce all over the place. You are also
>> likely to get a lot of wear unless you pressure feed lubricant. If you
>> do that oil will go everywhere. My router uses box ways on the Y and Z
>> axes with oil feed. It gets pretty messy at times.
>>
>> Most modern commercial routers and many machining centres use
>> rectangular linear ways, such as this
>> <
>> https://www.qualitybearingsonline.com/lwl25r240bhs2-iko-maintenance-free-linear-guide-rail/>.
>>
>> They are very rigid and lasts a long time with very little wear. The
>> only disadvantage is that you need to be careful to make sure everything
>> is perfectly aligned. These have very little give in them. Another
>> option is supported round rail such as this
>> <
>> https://www.amazon.co.uk/TEN-HIGH-Supported-SBR40UU-BlockBearing-Bearing/dp/B01N10JF5N>.
>>
>> For the sort of size machine you are talking about you'll need at least
>> 40mm round rail. Round rails wear faster than rectangular but are a lot
>> less fussy about alignment.
>>
>> > So, to sum up, with these kind of bearings I expect more resistance on
>> the
>> > joints, and also the router is 2 meters x 3,8 meters long so to have
>> enough
>> > rigidity I'm planning to use steel and cast iron, so that's why I'm
>> > oversizing the motors.
>>
>> To give you an idea about motor sizing the motors on my router (1 per
>> axis) are about 1.8kw and it's scary.  My tool changer is mounted on a
>> bracket made from 50mmx50mm box section. I messed up the tool change
>> sequencing a while back and it pushed the tool changer out of the way
>> without breaking a sweat. It tool a lot of effort with big levers to
>> twist it straight again. Here is a link to a similar machine to mine but
>> without a tool changer
>> <
>> https://www.bidspotter.co.uk/en-gb/auction-catalogues/cjm-asset/catalogue-id-cjm10389/lot-47df49af-bf1a-4676-ab88-a75a00f5f92b>.
>>
>> Lots of heavy steel and cast iron. Mine originally had 4 drill heads and
>> 2 spindles. If it was easy to dial back the power I would. If something
>> goes wrong the machine will keep pushing until something breaks.
>>
>> I do maintenance work on a router with 750W motors. A while back the
>> spindle stalled while it was cutting. It bent the 1/2" cutter nearly 90
>> degrees and carried on.
>>
>> Les
>>
>> On 04/10/2018 13:47, Leonardo Marsaglia wrote:
>> > First of all, thank you guys for your advices as always!
>> >
>> > I'm gonna try an asnwer this on one message because sadly gmail doesn't
>> > have the quote selected text feature anymore.
>> >
>> > About the oversized motors. Yes, I also think that for a normal router
>> 1 kw
>> > per side is too much. But the thing is, I'm planning to use round guides
>> > with 

Re: [Emc-users] Yet another topic about gantry homing

[Dave Cole]

You need to keep the drive system as simple as possible and keep 
backlash in mind.
Also, don't forget about the spring constant of any shaft you run across 
the gantry.  If you do that, you might want to
run a tube drive shaft rather than a solid shaft for more torsional 
rigidity.

There is nothing wrong with running two motors.
Excessive backlash will cause big problems.

Dave

On 10/4/2018 8:47 AM, Leonardo Marsaglia wrote:

First of all, thank you guys for your advices as always!

I'm gonna try an asnwer this on one message because sadly gmail doesn't
have the quote selected text feature anymore.

About the oversized motors. Yes, I also think that for a normal router 1 kw
per side is too much. But the thing is, I'm planning to use round guides
with bronze adjustable bearings. I decided this because I want more
rigidity for an eventual need of machining aluminum, and also because I
think this kind of guides with whipers are much more reliable than the
recirculating ball ones. Also, I don't think I can have the adjustable
feature with the slotted ball bearings. I'm attaching a picture of the
bearing I plan to make, there are no lube channels on the model but they
will be on the final part.

So, to sum up, with these kind of bearings I expect more resistance on the
joints, and also the router is 2 meters x 3,8 meters long so to have enough
rigidity I'm planning to use steel and cast iron, so that's why I'm
oversizing the motors. Besides, there's no much difference between a 400W
and a 1Kw  chinese servo motor and drive on ebay.

About how to drive and home the gantry. From what we've been talking and
thinking it through a little more, I'm thinking that the best solution is
the one Gregg suggested. To have a transversal shaft on the gantry driven
by the servo motor by a worm and gear reduction with the timing pulleys on
each end of the shaft driving the pinions. This way I can adjust and square
the two columns and it should stay squared at any time. This is really
important because this is going to be used by a regular operator, so this
has to be as reliable and fail proof as possible.

About the last question. Is there any disadvantage other than may be a
little more mechanical complexity with the one motor and shaft approach?
Because I've seen lots of routers driven with two motors that I almost
think it's mandatory for some reason.

Thanks again!

Leonardo








El jue., 4 oct. 2018 a las 0:03, Gregg Eshelman via Emc-users (<
emc-users@lists.sourceforge.net>) escribió:


  The easiest method is mechanically connect the two sides with a shaft
along the gantry and use one motor. Then it *cannot rack* or have any of
the other issues that can happen with driving both sides of a constrained
axis with two motors.
If you need more Z height, you can elevate the racks on the sides. Or run
chains or belts from the cross shaft ends down to stub shafts with the
pinion gears.

 On Wednesday, October 3, 2018, 4:03:48 AM MDT, Leonardo Marsaglia <
ldmarsag...@gmail.com> wrote:

  Hello to all!


About how to drive both Y joints as one axis: I've read that there's a way
of simply adding two Y joints for the Y axis in the 2.8 master branch but I
don't know if there's documentation available already.
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Re: [Emc-users] Yet another topic about gantry homing

[Les Newell]

Using two motors is mechanically simpler and has lower rotational 
inertia but I am not a fan of this setup. If you use a tube rather than 
a solid shaft, you won't add a lot of inertia. I'm thinking of building 
another plasma cutter and it will probably use a shaft rather than 2 motors.



But the thing is, I'm planning to use round guides
with bronze adjustable bearings.


Do you mean guides that are only supported at the ends? This is a very 
bad idea. They'll flex and bounce all over the place. You are also 
likely to get a lot of wear unless you pressure feed lubricant. If you 
do that oil will go everywhere. My router uses box ways on the Y and Z 
axes with oil feed. It gets pretty messy at times.


Most modern commercial routers and many machining centres use 
rectangular linear ways, such as this 
. 
They are very rigid and lasts a long time with very little wear. The 
only disadvantage is that you need to be careful to make sure everything 
is perfectly aligned. These have very little give in them. Another 
option is supported round rail such as this 
. 
For the sort of size machine you are talking about you'll need at least 
40mm round rail. Round rails wear faster than rectangular but are a lot 
less fussy about alignment.



So, to sum up, with these kind of bearings I expect more resistance on the
joints, and also the router is 2 meters x 3,8 meters long so to have enough
rigidity I'm planning to use steel and cast iron, so that's why I'm
oversizing the motors.


To give you an idea about motor sizing the motors on my router (1 per 
axis) are about 1.8kw and it's scary.  My tool changer is mounted on a 
bracket made from 50mmx50mm box section. I messed up the tool change 
sequencing a while back and it pushed the tool changer out of the way 
without breaking a sweat. It tool a lot of effort with big levers to 
twist it straight again. Here is a link to a similar machine to mine but 
without a tool changer 
. 
Lots of heavy steel and cast iron. Mine originally had 4 drill heads and 
2 spindles. If it was easy to dial back the power I would. If something 
goes wrong the machine will keep pushing until something breaks.


I do maintenance work on a router with 750W motors. A while back the 
spindle stalled while it was cutting. It bent the 1/2" cutter nearly 90 
degrees and carried on.


Les

On 04/10/2018 13:47, Leonardo Marsaglia wrote:

First of all, thank you guys for your advices as always!

I'm gonna try an asnwer this on one message because sadly gmail doesn't
have the quote selected text feature anymore.

About the oversized motors. Yes, I also think that for a normal router 1 kw
per side is too much. But the thing is, I'm planning to use round guides
with bronze adjustable bearings. I decided this because I want more
rigidity for an eventual need of machining aluminum, and also because I
think this kind of guides with whipers are much more reliable than the
recirculating ball ones. Also, I don't think I can have the adjustable
feature with the slotted ball bearings. I'm attaching a picture of the
bearing I plan to make, there are no lube channels on the model but they
will be on the final part.

So, to sum up, with these kind of bearings I expect more resistance on the
joints, and also the router is 2 meters x 3,8 meters long so to have enough
rigidity I'm planning to use steel and cast iron, so that's why I'm
oversizing the motors. Besides, there's no much difference between a 400W
and a 1Kw  chinese servo motor and drive on ebay.

About how to drive and home the gantry. From what we've been talking and
thinking it through a little more, I'm thinking that the best solution is
the one Gregg suggested. To have a transversal shaft on the gantry driven
by the servo motor by a worm and gear reduction with the timing pulleys on
each end of the shaft driving the pinions. This way I can adjust and square
the two columns and it should stay squared at any time. This is really
important because this is going to be used by a regular operator, so this
has to be as reliable and fail proof as possible.

About the last question. Is there any disadvantage other than may be a
little more mechanical complexity with the one motor and shaft approach?
Because I've seen lots of routers driven with two motors that I almost
think it's mandatory for some reason.

Thanks again!

Leonardo






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Re: [Emc-users] Yet another topic about gantry homing

[Gregg Eshelman via Emc-users]

 The easiest method is mechanically connect the two sides with a shaft along 
the gantry and use one motor. Then it *cannot rack* or have any of the other 
issues that can happen with driving both sides of a constrained axis with two 
motors.
If you need more Z height, you can elevate the racks on the sides. Or run 
chains or belts from the cross shaft ends down to stub shafts with the pinion 
gears.

On Wednesday, October 3, 2018, 4:03:48 AM MDT, Leonardo Marsaglia 
 wrote:  
 
 Hello to all!


About how to drive both Y joints as one axis: I've read that there's a way
of simply adding two Y joints for the Y axis in the 2.8 master branch but I
don't know if there's documentation available already.  
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Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

On Wed, Oct 3, 2018 at 6:45 AM Leonardo Marsaglia 
wrote:

>
> I was thinking about making a custom component for offsetting the index
> pulse on the encoders but I don't know if this approach will be reliable
> enough.
>

No.  DOn't do that.   It is far more accurate mohave the software
"remember" the number of steps between the index pules.  This As I wrote
above, this also provides a diagnostic that wiiltell you the machine is out
of adjustment  and needs help from a human.

I think with most motion control projects it is best to not build in
mechanical adjustments.  For example you screw the home switch in tight and
even Locktite the screws so it will never move.  Then if for some reason
zero needs to move you tell the software to "add 5" or whatever to the
values.   Anything that is adjustable will always get itself out of spec
require adjustment.

>
> --

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Yet another topic about gantry homing

[Chris Albertson]

I think using the index pulse will not detect "out of square".  The reason
is that you get out of square because of a "skipped step" on only one of
the motors.So your idea (I hate to say) works great only in cases where
it is not needed.   If the router never skips a step only one switch is
needed.

The reason to add the second switch is to detect the out of square
condition and if you mask the error by using index pulses to defeat the
purpose of using two switches.  You will NEVER get two mechanical switches
to 100% agree unless you  use a special home algorithm that first finds
approximately home by running fast into the switches then backs off and
single steps slowly, slowing settling time after each step.  Even then you
need to have the software "remember" the difference in step counts,   If
that ever changes then you are "out of square" and you sound some alarm so
the operator can fix it.But to find home you need one one switch and
use the second switch only to check if something moved.

Note the Prussia I3 printers and all the Prussia clones use a dual lead
screw on the z-axis.   This design might be the most common kind of drive.
There are two parallel screws with 8mm pitch.   The motors do 800 specs per
rev and so have a resolution of 0.01 mm and it is very reliable and stays
solid on square for months.  As long as you don't try and step to fast they
stay in sync "forever"

BTW the method used to square the system is easy, turn off power and rotate
one lead screw by hand and take measurements.




On Wed, Oct 3, 2018 at 3:02 AM Leonardo Marsaglia 
wrote:

> Hello to all!
>
> I'm building a CNC router for wood machining for a friend of mine and the
> best way I found to drive the Y joint for this particular design, given the
> size of the machine, is the following:
>
> One rack and pinion on each side of the longitudinal axis of the machine
> and each pinion conected to a servo motor using two steps of reduction with
> synchronous belts to achieve a 10 to 1 ratio.
>
> I've found several topics on the forum talking about the homing of an axis
> arranged like this. I guess to have screw regulated home switches for each
> Y joint is almost a must (in case you don't use linear scales). But I was
> wondering if it's possible to use ,in conjunction with that, the index
> pulse of an encoder coupled to directly to the pinion.
>
> My idea is to offset the index pulse on each encoder via HAL to make both
> sides of the Y joint trip the index pulse together and stay squared during
> homing. Is this a good practice?
>
> About how to drive both Y joints as one axis: I've read that there's a way
> of simply adding two Y joints for the Y axis in the 2.8 master branch but I
> don't know if there's documentation available already.
>
> But I was thinking about slaving one of the motors (using them as pulse and
> direction at the beginning to make things easier) and use the encoder on
> the pinion only for following error and homing. I don't like the open loop
> approach a lot, but I don't know if it's that easy to use them as servos in
> position mode without having too much trouble.
>
> Any thoughts?
>
> Thank you as always!
>
> Leonardo
>
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>


-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Yet another topic about gantry homing

[Dave Cole]

You will probably need two reduction stages to get a 10:1 belt drive 
reduction.
There are some fairly cheap servo motor gear boxes out there now being 
made in China.

That may be the cheaper/easier way to go.

FWIW, 1 KW servo motors x 2 is probably an overkill unless you want to 
go really fast or if your gantry is

heavy steel.

Dave

On 10/3/2018 9:41 AM, Leonardo Marsaglia wrote:

Sorry for the lack of detail, I wrote the message too fast this morning
when I just got up.

I'm planning to use 1 kw servos on each side with a max RPM of 3000. The
idea is to gear down from the motor to the pinion 10 to 1 using the timing
belts. The pinion I'm planning to use is a MOD 2 with 20 teeth. That would
give a theoretical linear max speed of 37 meters/minute.

I was thinking about making a custom component for offsetting the index
pulse on the encoders but I don't know if this approach will be reliable
enough.

El mié., 3 oct. 2018 a las 10:17, Todd Zuercher ()
escribió:


I haven't really looked at the documentation for Master lately, but the
means for setting up a multiple joint axis (like a gantry) was documented
reasonably well last time I checked.

My personal experience with rack and pinion driven wood routers is that
for stepper-motor drive you are going to want between 2.5-5
revolutions/inch of travel.  With a leaning towards the lower end of that
scale.  With a 2.5 rev/inch ratio and half stepping the machine should be
capable of 600ipm rapids and about 0.001" resolution.  If you are going to
run servo motors I would suggest a ratio probably double what you'd want
for a step-motor, but that will depend on the max rpm of your servo and
what you want your max feeds to be.

The 10:1 ratio you mention doesn't tell us much without the pinion size,
is that motor revs to pinion revs, or motor revs per unit length?

Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street
Dalton, Ohio 44618
Phone:  (330)828-2105ext. 2031

-Original Message-
From: Leonardo Marsaglia 
Sent: Wednesday, October 03, 2018 6:01 AM
To: Enhanced Machine Controller (EMC) 
Subject: [Emc-users] Yet another topic about gantry homing

Hello to all!

I'm building a CNC router for wood machining for a friend of mine and the
best way I found to drive the Y joint for this particular design, given the
size of the machine, is the following:

One rack and pinion on each side of the longitudinal axis of the machine
and each pinion conected to a servo motor using two steps of reduction with
synchronous belts to achieve a 10 to 1 ratio.

I've found several topics on the forum talking about the homing of an axis
arranged like this. I guess to have screw regulated home switches for each
Y joint is almost a must (in case you don't use linear scales). But I was
wondering if it's possible to use ,in conjunction with that, the index
pulse of an encoder coupled to directly to the pinion.

My idea is to offset the index pulse on each encoder via HAL to make both
sides of the Y joint trip the index pulse together and stay squared during
homing. Is this a good practice?

About how to drive both Y joints as one axis: I've read that there's a way
of simply adding two Y joints for the Y axis in the 2.8 master branch but I
don't know if there's documentation available already.

But I was thinking about slaving one of the motors (using them as pulse
and direction at the beginning to make things easier) and use the encoder
on the pinion only for following error and homing. I don't like the open
loop approach a lot, but I don't know if it's that easy to use them as
servos in position mode without having too much trouble.

Any thoughts?

Thank you as always!

Leonardo

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Re: [Emc-users] Yet another topic about gantry homing

[andy pugh]

On Wed, 3 Oct 2018 at 14:45, Leonardo Marsaglia  wrote:

> I was thinking about making a custom component for offsetting the index
> pulse on the encoders but I don't know if this approach will be reliable
> enough.

If some racking during homing is acceptable then you can adjust the
alignment of the two sides to their encoder pulses by changing the
HOME_OFFSET of each side.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916


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Re: [Emc-users] Yet another topic about gantry homing

[Leonardo Marsaglia]

Sorry for the lack of detail, I wrote the message too fast this morning
when I just got up.

I'm planning to use 1 kw servos on each side with a max RPM of 3000. The
idea is to gear down from the motor to the pinion 10 to 1 using the timing
belts. The pinion I'm planning to use is a MOD 2 with 20 teeth. That would
give a theoretical linear max speed of 37 meters/minute.

I was thinking about making a custom component for offsetting the index
pulse on the encoders but I don't know if this approach will be reliable
enough.

El mié., 3 oct. 2018 a las 10:17, Todd Zuercher ()
escribió:

> I haven't really looked at the documentation for Master lately, but the
> means for setting up a multiple joint axis (like a gantry) was documented
> reasonably well last time I checked.
>
> My personal experience with rack and pinion driven wood routers is that
> for stepper-motor drive you are going to want between 2.5-5
> revolutions/inch of travel.  With a leaning towards the lower end of that
> scale.  With a 2.5 rev/inch ratio and half stepping the machine should be
> capable of 600ipm rapids and about 0.001" resolution.  If you are going to
> run servo motors I would suggest a ratio probably double what you'd want
> for a step-motor, but that will depend on the max rpm of your servo and
> what you want your max feeds to be.
>
> The 10:1 ratio you mention doesn't tell us much without the pinion size,
> is that motor revs to pinion revs, or motor revs per unit length?
>
> Todd Zuercher
> P. Graham Dunn Inc.
> 630 Henry Street
> Dalton, Ohio 44618
> Phone:  (330)828-2105ext. 2031
>
> -Original Message-
> From: Leonardo Marsaglia 
> Sent: Wednesday, October 03, 2018 6:01 AM
> To: Enhanced Machine Controller (EMC) 
> Subject: [Emc-users] Yet another topic about gantry homing
>
> Hello to all!
>
> I'm building a CNC router for wood machining for a friend of mine and the
> best way I found to drive the Y joint for this particular design, given the
> size of the machine, is the following:
>
> One rack and pinion on each side of the longitudinal axis of the machine
> and each pinion conected to a servo motor using two steps of reduction with
> synchronous belts to achieve a 10 to 1 ratio.
>
> I've found several topics on the forum talking about the homing of an axis
> arranged like this. I guess to have screw regulated home switches for each
> Y joint is almost a must (in case you don't use linear scales). But I was
> wondering if it's possible to use ,in conjunction with that, the index
> pulse of an encoder coupled to directly to the pinion.
>
> My idea is to offset the index pulse on each encoder via HAL to make both
> sides of the Y joint trip the index pulse together and stay squared during
> homing. Is this a good practice?
>
> About how to drive both Y joints as one axis: I've read that there's a way
> of simply adding two Y joints for the Y axis in the 2.8 master branch but I
> don't know if there's documentation available already.
>
> But I was thinking about slaving one of the motors (using them as pulse
> and direction at the beginning to make things easier) and use the encoder
> on the pinion only for following error and homing. I don't like the open
> loop approach a lot, but I don't know if it's that easy to use them as
> servos in position mode without having too much trouble.
>
> Any thoughts?
>
> Thank you as always!
>
> Leonardo
>
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>
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Re: [Emc-users] Yet another topic about gantry homing

[Todd Zuercher]

I haven't really looked at the documentation for Master lately, but the means 
for setting up a multiple joint axis (like a gantry) was documented reasonably 
well last time I checked.  

My personal experience with rack and pinion driven wood routers is that for 
stepper-motor drive you are going to want between 2.5-5 revolutions/inch of 
travel.  With a leaning towards the lower end of that scale.  With a 2.5 
rev/inch ratio and half stepping the machine should be capable of 600ipm rapids 
and about 0.001" resolution.  If you are going to run servo motors I would 
suggest a ratio probably double what you'd want for a step-motor, but that will 
depend on the max rpm of your servo and what you want your max feeds to be.

The 10:1 ratio you mention doesn't tell us much without the pinion size, is 
that motor revs to pinion revs, or motor revs per unit length?

Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street 
Dalton, Ohio 44618
Phone:  (330)828-2105ext. 2031

-Original Message-
From: Leonardo Marsaglia  
Sent: Wednesday, October 03, 2018 6:01 AM
To: Enhanced Machine Controller (EMC) 
Subject: [Emc-users] Yet another topic about gantry homing

Hello to all!

I'm building a CNC router for wood machining for a friend of mine and the best 
way I found to drive the Y joint for this particular design, given the size of 
the machine, is the following:

One rack and pinion on each side of the longitudinal axis of the machine and 
each pinion conected to a servo motor using two steps of reduction with 
synchronous belts to achieve a 10 to 1 ratio.

I've found several topics on the forum talking about the homing of an axis 
arranged like this. I guess to have screw regulated home switches for each Y 
joint is almost a must (in case you don't use linear scales). But I was 
wondering if it's possible to use ,in conjunction with that, the index pulse of 
an encoder coupled to directly to the pinion.

My idea is to offset the index pulse on each encoder via HAL to make both sides 
of the Y joint trip the index pulse together and stay squared during homing. Is 
this a good practice?

About how to drive both Y joints as one axis: I've read that there's a way of 
simply adding two Y joints for the Y axis in the 2.8 master branch but I don't 
know if there's documentation available already.

But I was thinking about slaving one of the motors (using them as pulse and 
direction at the beginning to make things easier) and use the encoder on the 
pinion only for following error and homing. I don't like the open loop approach 
a lot, but I don't know if it's that easy to use them as servos in position 
mode without having too much trouble.

Any thoughts?

Thank you as always!

Leonardo

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