Re: [Emc-users] Need to select a timing belt type and size

[Chris Albertson]

On Thu, Feb 22, 2018 at 10:44 AM, N. Christopher Perry
 wrote:
>
>
>
> > On Feb 22, 2018, at 12:27 PM, Chris Albertson  
> > wrote
> Any pitch that provide at least 7 teeth on the motor sprocket is acceptable, 
> from a torque transmission / belt life stand point. On the other hand, the 
> larger the pitch the higher the peak torque you can transmit.  I should think 
> 3 mm is the right compromise.

What I found in the specs is that I could use a wider belt.   For
example a 12mm wide belt can transmit twice the torque of a 6mm wide
belt.But then I find that are side forces that force the belt in a
direction parallel to the pulley axis and the side force goes up as
the belt gets wider. Worse is that the larger GT2 pulleys lack
flanges.   The belt could walk of the pulley unless I resorted to high
belt tension and pulley flanges. The 9mm wide, 3 mm pitch belt
seems like it should work



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Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Need to select a timing belt type and size

[Chris Albertson]

On Thu, Mar 1, 2018 at 10:56 AM, jeremy youngs  wrote:
> Chris, what software are you using to generate gcode?


I download the STEP file from either Boston Gear or McMaster Carr or
some place like that can then import in into Fusion 360.  The import
is "perfect" in that I get a model made of curved surfaces without
"facets" so the model can be scaled with no loss of precision.   So it
is important to choose the "correct" format to download.  There are
quite a few options

One you import the model you almost certainly have to make changes.
The bore size of the hub is likely not to be what you want.   So first
step is to make the gear exactly as you would like it, including the
hub and even the size and thread pitch of the set screws.

Then there are two ways to make g-code:

1) If you are going to print the gear in plastic then Fusion has an
option to save the "body" as an STL file.  I set the allied error in
the STL to well less than 0.01mm.  Then the STL file is moved to
"Cura"  for slicing.   In Cura I set it up so the gear teeth get made
with 100% density (solid plastic) and the core to 50% density.  The
hub needs to be 100% too.  Layer hight at 0.1mm   It is a waste of
materials and TIME to make a 100% solid gear.   Cura will produce
g-code for the printer.

2) if you want to cut the gear in metal, Fusion 360 can do this
itself.  Although it does not know about speacilzed gear cutters and
will do it with a ball end mill and a 4th axis.  But this is about the
only way to make a helical gear in metal



-- 

Chris Albertson
Redondo Beach, California

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Re: [Emc-users] Need to select a timing belt type and size

[Gene Heskett]

On Thursday 01 March 2018 13:36:16 Chris Albertson wrote:

> Gene,
>
> Thanks that is some good real-world data.My plan with this Mini
> Mill is to do the conversion in steps.
>
> 1) Add the z-axis   The factory rack and pinyin z-axis setup is not
> very good and if nothing else a motorized screw based z-axis is a big
> improvement.
> 2) Do a quick and simple X, and Y axis conversion using the stock lead
> screws and 3D printed parts.

This is std 20 tpi threads, so doing a hot mold in alcetal is likely the 
best way to reduce the backlash, for a lot longer than adjusting the 
jackscrews can.

> 3) Re-do #2 using metal parts and zero backlash ballscrews

If you can find them in small enough to fit sizes, 8mm OD is crowded.
The screws I used were the "last of the Mohicans" that Stewart Stevensen 
had apparently stripped out of a surplus assembly of some unknown sort, 
I bought the last 3 he had. The nuts and screw fit were such that I was 
able to refill the nuts with .001" bigger balls I sourced from ebay.
2 of them are in my expended table micromill, and the last is now in the 
crossfeed of my 11x36 Sheldon. Those nuts were flangeless, so holder 
cages had to be made. The  last "cage" I made used setscrews to clamp 
lengthwise, with about 3/16" of old felt hat washers of both ends and 
cone shaped brass pieces to contain the felt, which serves as both 
oilers and debris wipers. I did somewhat the same in the micromill, but 
tapped one side of the holder block at 50 tpi, and made a threaded 
screwin plug to achieve a lengthwise grip on the nut and some of that 
same old felt hat. Those two have weed eater fuel lines to bring them 
oil from a manifold on the post, but the sheldon's cage was filled with 
silicon seal on the bottom, and I remove the bolt thru the top that 
connects to the crossfeed and refill it via the bolthole in the cage.

> 4) Add a 4th axis

Stay away from any table made in India. If you think Chinese stuff is 
schloppy, you'll get quickly informed its worse, lots worse than the 
Chinese stuff. I was dumb and bought a 4", but when I motorized it, the 
inconsistent backlash and lack of a set of table locks became quite 
obvious. And the odd angle the motor sticks out is a PITA, always 
hitting something. So look for something with a horizontal worm AND 
clearance enough to clear the table with the motor unless you want to 
make a pad to gain the clearance. I've been mentally plotting how to 
make a 45 degree tilt mount so the motor will stick out horizontally, 
but haven't yet found out where I stashed my round tuit, may have to 
make more of those if I can ever find a pattern that doesn't have 
copyright stamped all over it. :)

> I want to document the process so if it works someone else can
> duplicate it.
>
Thats to be desired.

> I ended up reading a lot of data from the belt supplier's web sites. 
> Yes GT2 profile should be used in every new design.  Only use
> trapezoid profile teeth as replacement parts.   The newer profile
> almost doubles the system performance and as you said, it uses a much
> lower belt tension too.
>
> The major different I find between ball and lead screws is friction. 
> A ball screw converts about 95% of the applied motor torque to thrust
> while a lead screw converts only 40% to 50% of the torque to thrust,
> the rest of the power goes into heating the screw and nut by sliding
> friction.  So in theory I should see at least a doubling on the z-axis
> performance you have. I don't know, we shall see.

My performance is limited more by low motor voltage (28 volts) than by 
friction. The diff between 28 volts and 40 volts, using the same 2m542 
driver, is eyebrow raising. Same motor, damper & driver on the 7x12's z 
axis, 2/1 gearing (not belt, gears, 40 on motor, 80 on screw), makes 
around 90 ipm on the lathe.

> My cheap ($190) 3D printer has me spoiled.  It routinely operates at
> 100 mm per second.  (in Imperial units that is 230 inches per minute.)
>  It can reliably move 30% faster.  My eye cannot really follow motion
> that quick. It can print anything I can draw.Now I want  milling
> machine like that.

So do I, till I think of the cost of broken tooling.

> BTW, I looked at your web site.   Noticed the wooden gear model that
> gets about 60:1 reduction.   That same principle is further developed
> by a guy who uses the name "gear down for what" in Thingiverse.  He
> has a very well engineered system of modular parts.  You can assemble
> high torque systems with no tools.  He uses ring gears that are thin
> enough to be flexible, you wrap it around the planet gears then press
> fit a round collar over the ring gear that stiffens it up.  At first
> look it seems more complex than a 15-speed automatic transmission but
> after some study is its very simple. He uses herringbone gears which
> are like two helical gears, one backwards glued together.  
> Herringbone gears are very strong and have zero side force but are
> near impossible to cut 

Re: [Emc-users] Need to select a timing belt type and size

[jeremy youngs]

Chris, what software are you using to generate gcode?
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Re: [Emc-users] Need to select a timing belt type and size

[Chris Albertson]

Gene,

Thanks that is some good real-world data.My plan with this Mini Mill is
to do the conversion in steps.

1) Add the z-axis   The factory rack and pinyin z-axis setup is not very
good and if nothing else a motorized screw based z-axis is a big
improvement.
2) Do a quick and simple X, and Y axis conversion using the stock lead
screws and 3D printed parts
3) Re-do #2 using metal parts and zero backlash ballscrews
4) Add a 4th axis

I want to document the process so if it works someone else can duplicate it.

I ended up reading a lot of data from the belt supplier's web sites.  Yes
GT2 profile should be used in every new design.  Only use trapezoid profile
teeth as replacement parts.   The newer profile almost doubles the system
performance and as you said, it uses a much lower belt tension too.

The major different I find between ball and lead screws is friction.  A
ball screw converts about 95% of the applied motor torque to thrust while a
lead screw converts only 40% to 50% of the torque to thrust, the rest of
the power goes into heating the screw and nut by sliding friction.  So in
theory I should see at least a doubling on the z-axis performance you have.
  I don't know, we shall see.

My cheap ($190) 3D printer has me spoiled.  It routinely operates at 100 mm
per second.  (in Imperial units that is 230 inches per minute.)  It can
reliably move 30% faster.  My eye cannot really follow motion that quick.
It can print anything I can draw.Now I want  milling machine like that.

BTW, I looked at your web site.   Noticed the wooden gear model that gets
about 60:1 reduction.   That same principle is further developed by a guy
who uses the name "gear down for what" in Thingiverse.  He has a very well
engineered system of modular parts.  You can assemble high torque systems
with no tools.  He uses ring gears that are thin enough to be flexible, you
wrap it around the planet gears then press fit a round collar over the ring
gear that stiffens it up.  At first look it seems more complex than a
15-speed automatic transmission but after some study is its very simple.
He uses herringbone gears which are like two helical gears, one backwards
glued together.   Herringbone gears are very strong and have zero side
force but are near impossible to cut in metal without a high-end 5-axis
mill and tiny ball end.   A spur gear version would be much easier. In
any case his innovation was to cut all the sun and plant gears on ONE
SHAFT.  And not to use any kind of gear carrier or bearings.  The lack of
carriers and bearing makes in very buildable.   He has versions that go
from 20:1 all that way to 1200:1 all based on the same design.  It is very
compact, no wasted space.
https://www.thingiverse.com/thing:2731585

Writing g-code by hand might be a problem for design this complex.   My
brain would explode if I tried to write the code for just one helical
gear.  But it's trivial to go to the Boston Gear web site and download a
CAD file for one of their stock helical gears.   Then I convert that to
g-code.   I don't have to understand involute curves.  I just download a
stock part from their catalog.  The McMaster Carr catalog works too. The
whole process takes 10 minutes and I end up with a 3MB g-code file.


On Sun, Feb 18, 2018 at 5:17 PM, Gene Heskett  wrote:

> On Sunday 18 February 2018 18:53:59 Chris Albertson wrote:
>
> > Question:  What would be the preferred timing belt for a new design?
> >
> > Here is the application.  I'm making a z-axis control for a Harbor
> > Freight mini mill (Sieg X2).   In this design a 5/8 diameter, 0.200
> > pitch ball screw is fixed and the nut spins.  The nut is driven by a
> > timing belt "about" 50 teeth and the motor has an about 25 tooth
> > pulley.   I'm thinking a 400 in/oz. NEMA 23 stepper should work.
> > Assuming the 2:1 reduction each 1.8 degree step lifts the head 0.0005
> > inches.  By 1/4 stepping I get 0.000125 per pulse.
> >
> > When looking for a good design for the mini mill I was looking for a
> > good place to put the ball screw.  This design places it very close to
> > the dove tail, almost touching it.  Maybe 0.1 inch in front of the
> > dovetail.  The ball screw goes right where the current rack it the
> > original design.  I will have to remove the rack to fit the screw.
> >
> > So I need to select a belt type and size.   My initial guess at this a
> > the GT2, 3mm pitch and 9mm wide.
> >
> > Some one else used a XL type 3/8 wide and 0.2 pitch but I'm reading
> > that XL is not the best for new designs as GT2 has a much improved
> > both profile that eliminates backlash.
> >
> > I started to calculate torque and load on the belt then thought "Why
> > bother?" the actual force is going to be whatever the motor can do as
> > I'll set the acceleration limits until it start skipping steps then
> > back up by about 30% or so.   I might go with a NEMA 34 1100 in/oz
> > motor if I need to.  So I might choose a belt that can handle 

Re: [Emc-users] Need to select a timing belt type and size

[Gene Heskett]

On Sunday 18 February 2018 20:17:06 Gene Heskett wrote:

> On Sunday 18 February 2018 18:53:59 Chris Albertson wrote:
> > Question:  What would be the preferred timing belt for a new design?
> >
> > Here is the application.  I'm making a z-axis control for a Harbor
> > Freight mini mill (Sieg X2).   In this design a 5/8 diameter, 0.200
> > pitch ball screw is fixed and the nut spins.  The nut is driven by a
> > timing belt "about" 50 teeth and the motor has an about 25 tooth
> > pulley.   I'm thinking a 400 in/oz. NEMA 23 stepper should work.
> > Assuming the 2:1 reduction each 1.8 degree step lifts the head
> > 0.0005 inches.  By 1/4 stepping I get 0.000125 per pulse.
> >
> > When looking for a good design for the mini mill I was looking for a
> > good place to put the ball screw.  This design places it very close
> > to the dove tail, almost touching it.  Maybe 0.1 inch in front of
> > the dovetail.  The ball screw goes right where the current rack it
> > the original design.  I will have to remove the rack to fit the
> > screw.
> >
> > So I need to select a belt type and size.   My initial guess at this
> > a the GT2, 3mm pitch and 9mm wide.
> >
> > Some one else used a XL type 3/8 wide and 0.2 pitch but I'm reading
> > that XL is not the best for new designs as GT2 has a much improved
> > both profile that eliminates backlash.

That was me, Gene, and in retrospect the GT2 is probably the better 
choice, as I have the belt tension right up to pretty hard on the motors 
bearings. Anything less and the backlash gets bad quickly. 17 teeth on 
the motor, 42 of the nut(s). nema 23 motor, double stack or around 270 
oz/in. With a damper of the rear of the motor, I can exceed 32 IPM on a 
10 tpi nook acme screw with only 28 volts to the motors. Mounted in 
front of the post, similar to what you've described but a little  
farther from the post.

Pix of my cobble job can be seen on my web page in the sig. Add emc to 
the base address or click on it. Pix 28 shows it moderately well.  A 3 
ft, 1.5x.250 strap was cut in two and made the stand above the post for 
the motor, a 3+ inch of 1/8th strap was bolted up the back long enough 
to get it welded, with a motor mount between the straps, and the whole 
thing bolted about 3x up each side to the post. Two tabs were welded on 
to project forward to hold the nuts bearings. Pix 33 shows it before 
mounting the motor or being installed on the post. The gearbox was 
turned 90 degrees to make room for the screw to pass and be bolted into 
the top of the sled casting. You can see the shopmade damper sticking up 
from the rear shaft of the motor in some of the pix.

Since those pix were taken, I have added a pair of 1/2" thick alu pieces 
around 7" long, with the center cut away, bolted to each side of the 
sled, carrying a skate bearing on the end to each "leg" to ride the face 
of the post, extending the effective wheelbase of the sled on the post 
by several inches, and as long as the post has a coat of vactra on it as 
I start the days use, all traces of stiction are gone. With that short a 
contact on the post, stiction is a huge problem, needing a dose of 
vactra (68) about every 30 minutes to even think about controlling it.

> > I started to calculate torque and load on the belt then thought "Why
> > bother?" the actual force is going to be whatever the motor can do
> > as I'll set the acceleration limits until it start skipping steps
> > then back up by about 30% or so.   I might go with a NEMA 34 1100
> > in/oz motor if I need to.  So I might choose a belt that can handle
> > whatever the 1100 in/oz motor can do.   Just looking to double check
> > GT2, 3mm pitch and 9mm wide is reasonable.
> >
> > So I guess the best way to ask the question is what kind of belts
> > are working well with motors in the 400 to 1100 in/oz. range.
> >
> > If there is any interest I'm modeling this in Fusion 360.  and can
> > share the CAD files
>
> Its been a while since I did my micromill, but ISTR I used the XL belt
> and its quite tight. Like you, I spin the nuts, doubled nook bronze
> ones, and my backlash stays below 3 thou. the screw is in front of the
> post by about 1/2 the distance between the post and the edge of the
> gearbox cover, which has been turned 90 degrees to get that clearance.
> the motor is an 8 wire good for a bit over 250 oz/in.  Works well. 
> you can see pix of it on my web page in the sig. The counter springing
> has been reworked a bit but the rest of the pix are still valid.
>
> Not a cad artist, so what you see came straight out of my head, quite
> a few years ago now. I write my own gcode.

-- 
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] Need to select a timing belt type and size

[Gene Heskett]

On Sunday 18 February 2018 18:53:59 Chris Albertson wrote:

> Question:  What would be the preferred timing belt for a new design?
>
> Here is the application.  I'm making a z-axis control for a Harbor
> Freight mini mill (Sieg X2).   In this design a 5/8 diameter, 0.200
> pitch ball screw is fixed and the nut spins.  The nut is driven by a
> timing belt "about" 50 teeth and the motor has an about 25 tooth
> pulley.   I'm thinking a 400 in/oz. NEMA 23 stepper should work.   
> Assuming the 2:1 reduction each 1.8 degree step lifts the head 0.0005
> inches.  By 1/4 stepping I get 0.000125 per pulse.
>
> When looking for a good design for the mini mill I was looking for a
> good place to put the ball screw.  This design places it very close to
> the dove tail, almost touching it.  Maybe 0.1 inch in front of the
> dovetail.  The ball screw goes right where the current rack it the
> original design.  I will have to remove the rack to fit the screw.
>
> So I need to select a belt type and size.   My initial guess at this a
> the GT2, 3mm pitch and 9mm wide.
>
> Some one else used a XL type 3/8 wide and 0.2 pitch but I'm reading
> that XL is not the best for new designs as GT2 has a much improved
> both profile that eliminates backlash.
>
> I started to calculate torque and load on the belt then thought "Why
> bother?" the actual force is going to be whatever the motor can do as
> I'll set the acceleration limits until it start skipping steps then
> back up by about 30% or so.   I might go with a NEMA 34 1100 in/oz
> motor if I need to.  So I might choose a belt that can handle whatever
> the 1100 in/oz motor can do.   Just looking to double check GT2, 3mm
> pitch and 9mm wide is reasonable.
>
> So I guess the best way to ask the question is what kind of belts are
> working well with motors in the 400 to 1100 in/oz. range.
>
> If there is any interest I'm modeling this in Fusion 360.  and can
> share the CAD files

Its been a while since I did my micromill, but ISTR I used the XL belt 
and its quite tight. Like you, I spin the nuts, doubled nook bronze 
ones, and my backlash stays below 3 thou. the screw is in front of the 
post by about 1/2 the distance between the post and the edge of the 
gearbox cover, which has been turned 90 degrees to get that clearance. 
the motor is an 8 wire good for a bit over 300 oz/in.  Works well.  you 
can see pix of it on my web page in the sig. The counter springing has 
been reworked a bit but the rest of the pix are still valid.

Not a cad artist, so what you see came straight out of my head, quite a 
few years ago now. I write my own gcode.

-- 
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] Need to select a timing belt type and size

[Jon Elson]

On 02/22/2018 11:56 AM, andy pugh wrote:

On 22 February 2018 at 18:27, Chris Albertson  wrote:


That is what I'm making too.  A rotating ball nut.   I looked at all the
ways there are to lift the head of a Siege X2 mini mill and I think the
question comes down to the location of the screw.  I think I will use the
space occupied by the factory installed column mounted rack.

I put the screw inside the column:
https://photos.app.goo.gl/HoPVUgjsAEOLwd293
With a shim strip in a tunnel to cover the slot:
https://photos.app.goo.gl/B8maY510qUPx00Qw1
It looked quite neat but was a terrible idea. Cutting the slot in the
middle of the dovetail massively reduced the torsional rigidity of the
column.
So don't do that :-)

I have a machine that is identical to an X2.  I found a tiny 
little ballscrew on eBay and mounted it to the front of the 
column.  I had to mill out a little relief in the slider 
that runs on the column.


I don't have a really clear photo of the ballscrew retrofit, 
but the top and bottom photos here do show part of it.

http://pico-systems.com/minimill.html

Jon

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Re: [Emc-users] Need to select a timing belt type and size

[N. Christopher Perry]

> On Feb 22, 2018, at 12:27 PM, Chris Albertson  
> wrote:
> 
> Andy,
> 
> That is what I'm making too.  A rotating ball nut.   I looked at all the
> ways there are to lift the head of a Siege X2 mini mill and I think the
> question comes down to the location of the screw.  I think I will use the
> space occupied by the factory installed column mounted rack.   The screw
> will be fixed to the head and lifted straight up by the rotating ball nut
> I'm using a 16mm dil x 2mm pitch screw.All other designs place a
> twisting force on the Z-axis dovetail
> 
> This belt will connect to a nut that looks like yours.But I read the
> belt literature and far and away the GT2 profiles seems best.   They are
> now calling it GT3 and say it interchanges with GT2 parts  The belt teeth
> are little semi circles.

The GT series all have effectively the same profile, just progressively better 
life / fatigue resistance.
> 
> My question was about pitch.  Should the belt pitch be 2mm, 3mm or 5mm.
> 
Any pitch that provide at least 7 teeth on the motor sprocket is acceptable, 
from a torque transmission / belt life stand point. On the other hand, the 
larger the pitch the higher the peak torque you can transmit.  I should think 3 
mm is the right compromise.

> So I look up technical data for the belts and each pitch has a minimum size
> pulley and different maximum RPMs.   Using 3mm pitch allows the motor to
> spin up to 5,000 RPM. I doubt I will run the stepper motor that fast
> 
>> 
N. Christopher Perry

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Re: [Emc-users] Need to select a timing belt type and size

[andy pugh]

On 22 February 2018 at 18:27, Chris Albertson  wrote:

> That is what I'm making too.  A rotating ball nut.   I looked at all the
> ways there are to lift the head of a Siege X2 mini mill and I think the
> question comes down to the location of the screw.  I think I will use the
> space occupied by the factory installed column mounted rack.

I put the screw inside the column:
https://photos.app.goo.gl/HoPVUgjsAEOLwd293
With a shim strip in a tunnel to cover the slot:
https://photos.app.goo.gl/B8maY510qUPx00Qw1
It looked quite neat but was a terrible idea. Cutting the slot in the
middle of the dovetail massively reduced the torsional rigidity of the
column.
So don't do that :-)

-- 
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] Need to select a timing belt type and size

[Chris Albertson]

Andy,

That is what I'm making too.  A rotating ball nut.   I looked at all the
ways there are to lift the head of a Siege X2 mini mill and I think the
question comes down to the location of the screw.  I think I will use the
space occupied by the factory installed column mounted rack.   The screw
will be fixed to the head and lifted straight up by the rotating ball nut
I'm using a 16mm dil x 2mm pitch screw.All other designs place a
twisting force on the Z-axis dovetail

This belt will connect to a nut that looks like yours.But I read the
belt literature and far and away the GT2 profiles seems best.   They are
now calling it GT3 and say it interchanges with GT2 parts  The belt teeth
are little semi circles.


My question was about pitch.  Should the belt pitch be 2mm, 3mm or 5mm.

So I look up technical data for the belts and each pitch has a minimum size
pulley and different maximum RPMs.   Using 3mm pitch allows the motor to
spin up to 5,000 RPM. I doubt I will run the stepper motor that fast

On Thu, Feb 22, 2018 at 3:30 AM, andy pugh  wrote:

> On 19 February 2018 at 09:08, Marcus Bowman
>  wrote:
>
> > I am planning to renew my belts after some 13 years fairly heavy use
> (ballscrews now worn), so I too have been pondering this problem.
> > The SDP/SI site at http://www.sdp-si.com/products/details/timing-belt-
> detail.php#gt2
>
> I have always used the metric "T" profile belts, also listed on the link
> above.
>
> I don't know if they are technically suprior or inferior to other
> systems, but they are readily available (from RS and other UK
> supliers) and I have a pully hob so can make my own pulleys.
>
> Here is a rather special one I made for a rotating ball-nut
> arrangement. (that's the ball nut in the middle).
> https://photos.app.goo.gl/1dJiuUVVdZmrghI93
> It was for the X axis of my mill, which is why the hob feed rate was
> uneven and too fast.
>
> --
> 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
>
> 
> --
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> ___
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> https://lists.sourceforge.net/lists/listinfo/emc-users
>



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Chris Albertson
Redondo Beach, California
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Re: [Emc-users] Need to select a timing belt type and size

[andy pugh]

On 19 February 2018 at 09:08, Marcus Bowman
 wrote:

> I am planning to renew my belts after some 13 years fairly heavy use 
> (ballscrews now worn), so I too have been pondering this problem.
> The SDP/SI site at 
> http://www.sdp-si.com/products/details/timing-belt-detail.php#gt2

I have always used the metric "T" profile belts, also listed on the link above.

I don't know if they are technically suprior or inferior to other
systems, but they are readily available (from RS and other UK
supliers) and I have a pully hob so can make my own pulleys.

Here is a rather special one I made for a rotating ball-nut
arrangement. (that's the ball nut in the middle).
https://photos.app.goo.gl/1dJiuUVVdZmrghI93
It was for the X axis of my mill, which is why the hob feed rate was
uneven and too fast.

-- 
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] Need to select a timing belt type and size

[N. Christopher Perry]

> On Feb 18, 2018, at 6:53 PM, Chris Albertson  
> wrote:
> 
> Question:  What would be the preferred timing belt for a new design?
> 
> Here is the application.  I'm making a z-axis control for a Harbor Freight
> mini mill (Sieg X2).   In this design a 5/8 diameter, 0.200 pitch ball
> screw is fixed and the nut spins.  The nut is driven by a timing belt
> "about" 50 teeth and the motor has an about 25 tooth pulley.   I'm thinking
> a 400 in/oz. NEMA 23 stepper should work.Assuming the 2:1 reduction
> each 1.8 degree step lifts the head 0.0005 inches.  By 1/4 stepping I get
> 0.000125 per pulse.
> 
> When looking for a good design for the mini mill I was looking for a good
> place to put the ball screw.  This design places it very close to the dove
> tail, almost touching it.  Maybe 0.1 inch in front of the dovetail.  The
> ball screw goes right where the current rack it the original design.  I
> will have to remove the rack to fit the screw.
> 
> So I need to select a belt type and size.   My initial guess at this a the
> GT2, 3mm pitch and 9mm wide.
> 
I’ve used almost the same configuration on my scratch built mini-mill and it 
has worked fine for 8 years.  The GT2 belts are superior in most respects, 
particularly because they have an involute profile.  This reduces noise and 
increases effective stiffness.

> Some one else used a XL type 3/8 wide and 0.2 pitch but I'm reading that XL
> is not the best for new designs as GT2 has a much improved both profile
> that eliminates backlash.

The XL doesn’t really have backlash, but does have more compliance for a given 
belt tension, as the profile allows the teeth to generate higher separation 
loads which allow them to ‘ride up’ some under high loads.  As such, you end up 
needing higher tensions to transmit a given torque.

> 
> I started to calculate torque and load on the belt then thought "Why
> bother?" the actual force is going to be whatever the motor can do as I'll
> set the acceleration limits until it start skipping steps then back up by
> about 30% or so.   

The real reason to calculate the forces is to make sure you have sufficient 
static tension so that under max load the ‘slack’ side of the belt never 
actually goes slack.  If that happens the belt will unwrap from the slack side 
of the drive sprocket and might skip a tooth.  According to the literature, 
this represents a belt drive failure and will rapidly destroy a belt by 
overload the cords and breaking strands in them.  Broken strands lead to lose 
of tension, and the cycle rapidly repeats until the belt either looses sections 
of teeth or falls apart.

> I might go with a NEMA 34 1100 in/oz motor if I need
> to.  So I might choose a belt that can handle whatever the 1100 in/oz motor
> can do.   Just looking to double check GT2, 3mm pitch and 9mm wide is
> reasonable.
> 
> So I guess the best way to ask the question is what kind of belts are
> working well with motors in the 400 to 1100 in/oz. range.
> 
> If there is any interest I'm modeling this in Fusion 360.  and can share
> the CAD files
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
> --
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
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Re: [Emc-users] Need to select a timing belt type and size

[Marcus Bowman]

On 18 Feb 2018, at 23:53, Chris Albertson wrote:
> So I need to select a belt type and size.   My initial guess at this a the
> GT2, 3mm pitch and 9mm wide.
> 


I am planning to renew my belts after some 13 years fairly heavy use 
(ballscrews now worn), so I too have been pondering this problem.
The SDP/SI site at 
http://www.sdp-si.com/products/details/timing-belt-detail.php#gt2
 tells me that:

The PowerGrip GT3 Belt Drive System is the newest design and offers additional 
benefits over GT2. The improved construction and material compound provides 
superior load bearing capacity. The GT2 Belts are being phased out and replaced 
by the new GT3 Belt Drive System

Marcus

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[Emc-users] Need to select a timing belt type and size

[Chris Albertson]

Question:  What would be the preferred timing belt for a new design?

Here is the application.  I'm making a z-axis control for a Harbor Freight
mini mill (Sieg X2).   In this design a 5/8 diameter, 0.200 pitch ball
screw is fixed and the nut spins.  The nut is driven by a timing belt
"about" 50 teeth and the motor has an about 25 tooth pulley.   I'm thinking
a 400 in/oz. NEMA 23 stepper should work.Assuming the 2:1 reduction
each 1.8 degree step lifts the head 0.0005 inches.  By 1/4 stepping I get
0.000125 per pulse.

When looking for a good design for the mini mill I was looking for a good
place to put the ball screw.  This design places it very close to the dove
tail, almost touching it.  Maybe 0.1 inch in front of the dovetail.  The
ball screw goes right where the current rack it the original design.  I
will have to remove the rack to fit the screw.

So I need to select a belt type and size.   My initial guess at this a the
GT2, 3mm pitch and 9mm wide.

Some one else used a XL type 3/8 wide and 0.2 pitch but I'm reading that XL
is not the best for new designs as GT2 has a much improved both profile
that eliminates backlash.

I started to calculate torque and load on the belt then thought "Why
bother?" the actual force is going to be whatever the motor can do as I'll
set the acceleration limits until it start skipping steps then back up by
about 30% or so.   I might go with a NEMA 34 1100 in/oz motor if I need
to.  So I might choose a belt that can handle whatever the 1100 in/oz motor
can do.   Just looking to double check GT2, 3mm pitch and 9mm wide is
reasonable.

So I guess the best way to ask the question is what kind of belts are
working well with motors in the 400 to 1100 in/oz. range.

If there is any interest I'm modeling this in Fusion 360.  and can share
the CAD files

-- 

Chris Albertson
Redondo Beach, California
--
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