Re: [Emc-users] Helical interpolation not quite round, WTF?

[Gene Heskett]

On Tuesday 25 September 2012 23:23:36 Igor Chudov did opine:

> I have a routine that lets me mill a deep circle in several passes,
> typically to cutout circles from plates.
> 
> Something strange is going on and the resulting shape is not exactly
> round. It can be best described as a circle with humps.
> 
> The routine is below. It is basically a while loop, milling
> progressively deeper until Z reaches the required depth. Every loop
> consists of two half circles milled helically, with the end mill going
> down along a spiral.
> 
> Any idea why the shape may not end up being circular?
> 
> Thanks
> 
> Routine attached.
> 
> (Copyright - Igor Chudov, released under GNU Public License V3)
> 
> O sub (circular groove, good for milling through holes
> too) # = #1 (X center)
>   # = #2 (Y center)
>   #  = #3 (safe height)
>   #  = #4 (depth of milling)
>   # = #5 (outside radius)
>   #  = #6 (end mill diameter)
>   #  = #7 (feed rate)
>   #  = #8 (z step, per circle, optional)
> 
>   O if [ # NE 0 ]
> F#
>   O endif
> 
>   O if [ # EQ 0 ]
> # = [#/3]
>   O endif
> 
>   # = #
>   # = [# - #/2]
> 
>   G0 Z#
>   G4 P0
>   G0 X[# + #] Y#
> 
>   O while [ 1 ]
> 
> O if [ # - # LT #]
>   # = [# - #]
> O endif
> 
> G2 X[# - #] Y# Z[# - #/2] R#
> G2 X[# + #] Y# Z[# - #] R#
> 
> # = [# - #]
> 
> O if [ # LE # ]
>   O break
> O endif
> 
>   O endwhile
> 
>   G2 X[# - #] Y# R#
>   G2 X[# + #] Y# R#
> 
>   G0 Z#
> 
> O endsub
> 
> M2

The first thing I'd check would be uncompensated backlash.  Then it would 
go to damaged screws, like a highly used area wobbled out.  Third would be 
scaling error on one axis, but thats fairly easy to check.

Cheers, Gene
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My web page:  is up!
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Jon Elson]

Igor Chudov wrote:
> Humps are
>
> 1) Northwest corner, biggest hump, 1mm tall by 20mm wide
> 2) Northeast corner, 0.5mm by 15mm wide
>   
This has to be a program error.  And, you should be able to EASILY see 
this on
the Axis 3D display.  Load the program, and then use the mouse buttons to
tilt the display until you are looking flat at the XY plane.  Zoom in 
and pan
around the circle.  The deviation on successive depth passes should show up
very easily if it is a mm deep into the wall of the hole.

If it shows up on the preview, that gets backlash and the entire motion 
system
off the hook.

Jon

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Re: [Emc-users] 100 watt 3 phase AC servo amplifier?

[Jon Elson]

Jason Burton wrote:
>
> Hall effect sensors >> assuming straight contact closures here, not active
> signals, right?
>   
Well, the typical real Hall sensor in the motor needs +5 V, but is often 
like
a contact closure to ground.  So, the Hall sensor package has 5 wires,
+5, Ground and 3 signal wires.
> I am at a decision fork.
> 1) Spend money and time on this hardware, get better performance. Or
> 2) Sell this and build my own repstrap like version run by with steppers
> and linuxcnc.
>
>   
Well, brushless servos have WAY more performance than steppers.  
Although, in
the repstrap size machine, it may not make a whole lot of difference.
> I intend to put a flame cutting head on it for small format steel sheet and
> plate.
>
>   
Hmm, I can't imagine a repstrap with a torch on it.
> With a head swap and sitting on top of a Z stage I want to experiment with
> liquid binder based 3D powder prints.
>
> I already have steppers, several drivers, acme leadscrews. It just seemed
> tantalizing having the complete xy built already minus the control.
>
> Don't really want to put $300+ into an experimentation platform that ends
> up slower than what i could build from my "junk" box.
>   
Well, probably won't be slower.  I think your motors were rated to 3000 
RPM at ~200 V, so
I'm guessing you'd get about 1800 RPM with my servo amps.  1800 RPM with 
a 20 TPI
leadscrew would give 90 IPM, but if the leadscrew had slower pitch, you 
could get 360
IPM at 5 TPI, for instance.  Not sure you can actually spin a thin 
leadscrew at 1800
RPM without bending it, so the motor may not be the limiting factor.

You certainly cannot get 1800 RPM with most stepper motors, they will 
severely overheat
at sustained speeds over 1000 RPM.

Jon

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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Jon Elson]

Igor Chudov wrote:
> Andy, thanks, what is P? Number of passes?
>
> The problem is that the lumps do not look like caused by backlash.
>
> There is one place where there is a lump, caused by all passes except the
> first one. I am very puzzled.
>   
Can you blow up the Axis plot window and see the lump?  You can also 
plot velocity
in Halscope and look for non-sinusoidal bumps there.

You might try makebore.c or makering.c from my web
page http://pico-systems.com/gcode.html
and see if you get different results.  makering.c makes a slightly undersize
circular pass in 4 quadrants X the number of depth steps, then spirals out
and makes 4 more quadrants
at the finish diameter.  It definitely does not give bumps with a 2.4.x
LinuxCNC on an older Linux kernel.  I have not done any precision work
with 2.5 (my production system runs a bit behind on updates).

Jon

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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Terry Christophersen]

Sometimes milling in the opposite direction will help.Rough one direction then
put in a finish pass in the other.
Looking at your code I see you have a G2.Unless this is plastic or something 
really gummy you should be using G3 for ID work.Or you are using left handed 
mills.
Climb milling is the way to do most everything.

Terry




- Original Message -
From: dave 
To: Enhanced Machine Controller (EMC) 
Cc: 
Sent: Tuesday, September 25, 2012 3:08 PM
Subject: Re: [Emc-users] Helical interpolation not quite round, WTF?

On Tue, 2012-09-25 at 15:13 -0400, Stephen Dubovsky wrote:
> How big are the "humps"?  How many are there?
> 
> Are you in exact stop mode?  If motion stops at the beginning/end of
> each semicircle then you will get a little hump from springback during
> the pause.  Lead-in & out are typ used when cutting IDs to prevent
> that.
> 
> Stephen
> 
Ah! Both good questions I should have been smart enough to ask. Since my
mill is not as stiff as would be ideal I tend to take small Z
increments/360 degrees and work my way down taking at least an extra
pass or two at the max depth as spring passes. 

To extend Stephen's question: where are the humps, exactly at 0, 90, 180
& 270 or offset some. Are they deep enough to not be backlash anomalies?

Dave
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Re: [Emc-users] [off] Lost PLA Casting

[Jeshua Lacock]

On Sep 25, 2012, at 9:54 AM, Kent A. Reed wrote:

> Congratulations, Jeshua. Your project made Hackaday today. I hope your 
> website is ready for the inevitable bump in traffic.

Thanks Kent!

Ready, willing and able!!!


Cheers,

Jeshua Lacock
Founder/Engineer
3DTOPO Incorporated

Phone: 208.462.4171


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Re: [Emc-users] [off] Lost PLA Casting

[Jeshua Lacock]

On Sep 24, 2012, at 6:33 AM, Steve Stallings wrote:

> It looks like he used a crucible lifter to do the
> pour. 

Guilty as charged!


Jeshua Lacock
Founder/Engineer
3DTOPO Incorporated

Phone: 208.462.4171


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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Ben Potter]

It's pretty unlikely, but with the first pass being free of humps I'd be
tempted to look at tool deflection. If your first pass is milling in from
fresh air it'll take a lighter cut, the heavier (and more consistent) cut on
each subsequent pass could then be deflecting slightly. 

If this is the case, and you don't find a better solution - you can always
do the cut in two passes, cut it 1-3 mm undersize then do a quick finish
pass to cleanup. Not ideal, but I tend to have to do this with smaller
diameter cutters on my non-rigid router.

Your sub looks OK, but I'd also be tempted to use G2 I J Z P directly to
rule out any... odd motion planning.

Ben

-Original Message-
From: Igor Chudov [mailto:ichu...@gmail.com] 
Sent: 25 September 2012 21:31
To: dengv...@charter.net; Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] Helical interpolation not quite round, WTF?

Humps are

1) Northwest corner, biggest hump, 1mm tall by 20mm wide
2) Northeast corner, 0.5mm by 15mm wide

On Tue, Sep 25, 2012 at 3:08 PM, dave  wrote:

> On Tue, 2012-09-25 at 15:13 -0400, Stephen Dubovsky wrote:
> > How big are the "humps"?  How many are there?
> >
> > Are you in exact stop mode?  If motion stops at the beginning/end of 
> > each semicircle then you will get a little hump from springback 
> > during the pause.  Lead-in & out are typ used when cutting IDs to 
> > prevent that.
> >
> > Stephen
> >
> Ah! Both good questions I should have been smart enough to ask. Since 
> my mill is not as stiff as would be ideal I tend to take small Z
> increments/360 degrees and work my way down taking at least an extra 
> pass or two at the max depth as spring passes.
>
> To extend Stephen's question: where are the humps, exactly at 0, 90, 
> 180 & 270 or offset some. Are they deep enough to not be backlash
anomalies?
>
> Dave
> >
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Igor Chudov]

Humps are

1) Northwest corner, biggest hump, 1mm tall by 20mm wide
2) Northeast corner, 0.5mm by 15mm wide

On Tue, Sep 25, 2012 at 3:08 PM, dave  wrote:

> On Tue, 2012-09-25 at 15:13 -0400, Stephen Dubovsky wrote:
> > How big are the "humps"?  How many are there?
> >
> > Are you in exact stop mode?  If motion stops at the beginning/end of
> > each semicircle then you will get a little hump from springback during
> > the pause.  Lead-in & out are typ used when cutting IDs to prevent
> > that.
> >
> > Stephen
> >
> Ah! Both good questions I should have been smart enough to ask. Since my
> mill is not as stiff as would be ideal I tend to take small Z
> increments/360 degrees and work my way down taking at least an extra
> pass or two at the max depth as spring passes.
>
> To extend Stephen's question: where are the humps, exactly at 0, 90, 180
> & 270 or offset some. Are they deep enough to not be backlash anomalies?
>
> Dave
> >
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[dave]

On Tue, 2012-09-25 at 15:13 -0400, Stephen Dubovsky wrote:
> How big are the "humps"?  How many are there?
> 
> Are you in exact stop mode?  If motion stops at the beginning/end of
> each semicircle then you will get a little hump from springback during
> the pause.  Lead-in & out are typ used when cutting IDs to prevent
> that.
> 
> Stephen
> 
Ah! Both good questions I should have been smart enough to ask. Since my
mill is not as stiff as would be ideal I tend to take small Z
increments/360 degrees and work my way down taking at least an extra
pass or two at the max depth as spring passes. 

To extend Stephen's question: where are the humps, exactly at 0, 90, 180
& 270 or offset some. Are they deep enough to not be backlash anomalies?

Dave
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Igor Chudov]

On Tue, Sep 25, 2012 at 2:13 PM, Stephen Dubovsky wrote:

> How big are the "humps"?  How many are there?
>
>
There is one big hump on an about 4 inch circle. This hump is about 1mm
tall and 20mm wide.

It appears consistently on all passes, except the first one.

There is also a much smaller hump in another quadrant, visible, but
smaller.

I am not` in exact stop mode.

i


> Are you in exact stop mode?  If motion stops at the beginning/end of
> each semicircle then you will get a little hump from springback during
> the pause.  Lead-in & out are typ used when cutting IDs to prevent
> that.
>
> Stephen
>
>
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Stephen Dubovsky]

How big are the "humps"?  How many are there?

Are you in exact stop mode?  If motion stops at the beginning/end of
each semicircle then you will get a little hump from springback during
the pause.  Lead-in & out are typ used when cutting IDs to prevent
that.

Stephen

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Re: [Emc-users] Helical interpolation not quite round, WTF?

[andy pugh]

On 25 September 2012 20:01, Igor Chudov  wrote:
> Andy, thanks, what is P? Number of passes?

Yes.

> The problem is that the lumps do not look like caused by backlash.

Odd, then.

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Re: [Emc-users] 100 watt 3 phase AC servo amplifier?

[Jason Burton]

On Sep 22, 2012 10:39 PM, "Jon Elson"  wrote:
>
> Viesturs La-cis wrote:
> > 2012/9/22 Jason Burton :
> >
> >> Does Mesa or Pico (or another vendor) make a small, inexpensive amp for
> >> this size 3 phase servo?
> >>
> >>
> >
> > Mesa has small BLDC servo amps, but their rated voltage is much lower
> > - 7i39HV is 50 VDC.
> > I do not know about Pico Systems products.
> >
> Our PWM servo amp has been tested to 122 V, and is good to 20 A.
> It can be used with either Mesa or Pico Systems controller boards.
> It needs the "Hall" signals from the motor for commutation.
>
> Jon
>

Hall effect sensors >> assuming straight contact closures here, not active
signals, right?

I am at a decision fork.
1) Spend money and time on this hardware, get better performance. Or
2) Sell this and build my own repstrap like version run by with steppers
and linuxcnc.

I intend to put a flame cutting head on it for small format steel sheet and
plate.

With a head swap and sitting on top of a Z stage I want to experiment with
liquid binder based 3D powder prints.

I already have steppers, several drivers, acme leadscrews. It just seemed
tantalizing having the complete xy built already minus the control.

Don't really want to put $300+ into an experimentation platform that ends
up slower than what i could build from my "junk" box.

All thoughts/comments welcome!

Best,
Jason
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[Igor Chudov]

Andy, thanks, what is P? Number of passes?

The problem is that the lumps do not look like caused by backlash.

There is one place where there is a lump, caused by all passes except the
first one. I am very puzzled.

i


On Tue, Sep 25, 2012 at 1:40 PM, andy pugh  wrote:

> On 25 September 2012 19:20, Igor Chudov  wrote:
> > I have a routine that lets me mill a deep circle in several passes,
> > typically to cutout circles from plates.
>
> You ought to be able to do this with one line of G-code?
>
> G2 I[
> Lumps at the 4 quadrants would normally be due to backlash problems.
>
> --
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> If you can't fix it, you don't own it.
> http://www.ifixit.com/Manifesto
>
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[N. Christopher Perry]

Igor,

I don't have an answer for you, other than to check on how you've defined you 
trajectory planning accuracy outside of this routine.

Why are you using two half circles?  You could just send the cutter back to the 
starting xy location in a single G2 instruction.

N. Christopher Perry

On Sep 25, 2012, at 14:20, Igor Chudov  wrote:

> I have a routine that lets me mill a deep circle in several passes,
> typically to cutout circles from plates.
> 
> Something strange is going on and the resulting shape is not exactly round.
> It can be best described as a circle with humps.
> 
> The routine is below. It is basically a while loop, milling progressively
> deeper until Z reaches the required depth. Every loop consists of two half
> circles milled helically, with the end mill going down along a spiral.
> 
> Any idea why the shape may not end up being circular?
> 
> Thanks
> 
> Routine attached.
> 
> (Copyright - Igor Chudov, released under GNU Public License V3)
> 
> O sub (circular groove, good for milling through holes too)
>  # = #1 (X center)
>  # = #2 (Y center)
>  #  = #3 (safe height)
>  #  = #4 (depth of milling)
>  # = #5 (outside radius)
>  #  = #6 (end mill diameter)
>  #  = #7 (feed rate)
>  #  = #8 (z step, per circle, optional)
> 
>  O if [ # NE 0 ]
>F#
>  O endif
> 
>  O if [ # EQ 0 ]
># = [#/3]
>  O endif
> 
>  # = #
>  # = [# - #/2]
> 
>  G0 Z#
>  G4 P0
>  G0 X[# + #] Y#
> 
>  O while [ 1 ]
> 
>O if [ # - # LT #]
>  # = [# - #]
>O endif
> 
>G2 X[# - #] Y# Z[# - #/2] R#
>G2 X[# + #] Y# Z[# - #] R#
> 
># = [# - #]
> 
>O if [ # LE # ]
>  O break
>O endif
> 
>  O endwhile
> 
>  G2 X[# - #] Y# R#
>  G2 X[# + #] Y# R#
> 
>  G0 Z#
> 
> O endsub
> 
> M2
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Re: [Emc-users] Helical interpolation not quite round, WTF?

[dave]

On Tue, 2012-09-25 at 13:20 -0500, Igor Chudov wrote:
> I have a routine that lets me mill a deep circle in several passes,
> typically to cutout circles from plates.
> 
> Something strange is going on and the resulting shape is not exactly round.
> It can be best described as a circle with humps.
> 
> The routine is below. It is basically a while loop, milling progressively
> deeper until Z reaches the required depth. Every loop consists of two half
> circles milled helically, with the end mill going down along a spiral.
> 
> Any idea why the shape may not end up being circular?
> 
> Thanks
> 
> Routine attached.
> 
> (Copyright - Igor Chudov, released under GNU Public License V3)
> 
> O sub (circular groove, good for milling through holes too)
>   # = #1 (X center)
>   # = #2 (Y center)
>   #  = #3 (safe height)
>   #  = #4 (depth of milling)
>   # = #5 (outside radius)
>   #  = #6 (end mill diameter)
>   #  = #7 (feed rate)
>   #  = #8 (z step, per circle, optional)
> 
>   O if [ # NE 0 ]
> F#
>   O endif
> 
>   O if [ # EQ 0 ]
> # = [#/3]
>   O endif
> 
>   # = #
>   # = [# - #/2]
> 
>   G0 Z#
>   G4 P0
>   G0 X[# + #] Y#
> 
>   O while [ 1 ]
> 
> O if [ # - # LT #]
>   # = [# - #]
> O endif
> 
> G2 X[# - #] Y# Z[# - #/2] R#
> G2 X[# + #] Y# Z[# - #] R#
> 
> # = [# - #]
> 
> O if [ # LE # ]
>   O break
> O endif
> 
>   O endwhile
> 
>   G2 X[# - #] Y# R#
>   G2 X[# + #] Y# R#
> 
>   G0 Z#
> 
> O endsub
> 
> M2
Hi Igor,
Just off the top of my head I suspect that your program is fine; but the
machine is well used and has measurable backlash. In a perfect machine
you get real axis reversal ( X | Y ) every 90 degrees. If your
ballscrews (lead screw) have backlash then you have to catch up with
that before the axis actually changes direction. 
Since the slope is small around the inflection points not much happens
until you take up the slack and then you see the actual reversal. Might
be as much as 10 degrees off the ideal. Multiple passes may make it look
better but will not necessarily improve the precision. Backlash comp
does not fix this; only throwing $$$ at the machine. :-(

I hope it turns out to be something fixable without the injection of
many $. 

Dave


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Re: [Emc-users] Helical interpolation not quite round, WTF?

[andy pugh]

On 25 September 2012 19:20, Igor Chudov  wrote:
> I have a routine that lets me mill a deep circle in several passes,
> typically to cutout circles from plates.

You ought to be able to do this with one line of G-code?

G2 I[http://www.ifixit.com/Manifesto

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[Emc-users] Helical interpolation not quite round, WTF?

[Igor Chudov]

I have a routine that lets me mill a deep circle in several passes,
typically to cutout circles from plates.

Something strange is going on and the resulting shape is not exactly round.
It can be best described as a circle with humps.

The routine is below. It is basically a while loop, milling progressively
deeper until Z reaches the required depth. Every loop consists of two half
circles milled helically, with the end mill going down along a spiral.

Any idea why the shape may not end up being circular?

Thanks

Routine attached.

(Copyright - Igor Chudov, released under GNU Public License V3)

O sub (circular groove, good for milling through holes too)
  # = #1 (X center)
  # = #2 (Y center)
  #  = #3 (safe height)
  #  = #4 (depth of milling)
  # = #5 (outside radius)
  #  = #6 (end mill diameter)
  #  = #7 (feed rate)
  #  = #8 (z step, per circle, optional)

  O if [ # NE 0 ]
F#
  O endif

  O if [ # EQ 0 ]
# = [#/3]
  O endif

  # = #
  # = [# - #/2]

  G0 Z#
  G4 P0
  G0 X[# + #] Y#

  O while [ 1 ]

O if [ # - # LT #]
  # = [# - #]
O endif

G2 X[# - #] Y# Z[# - #/2] R#
G2 X[# + #] Y# Z[# - #] R#

# = [# - #]

O if [ # LE # ]
  O break
O endif

  O endwhile

  G2 X[# - #] Y# R#
  G2 X[# + #] Y# R#

  G0 Z#

O endsub

M2
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Re: [Emc-users] [off] Lost PLA Casting

[Kent A. Reed]

On 9/23/2012 11:12 PM, Kent A. Reed wrote:
> On 9/23/2012 10:25 PM, Jeshua Lacock wrote:
>> Greetings,
>>
>> This web page describes the process I used going from OpenSCAD to 
>> casted aluminum parts in a day:
>>
>> http://3dtopo.com/lostPLA/
>>
>> The casted parts are ultimately going to be controlled by LinuxCNC.
>>
>>
>>
>

Congratulations, Jeshua. Your project made Hackaday today. I hope your 
website is ready for the inevitable bump in traffic.

Regards,
Kent


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