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Mach 4 not following toolpath
« on: November 13, 2018, 04:33:58 PM »
I've found an issue with the Mach-4-powered CNC router at my hackerspace.  It's a generic 2.5D machine that controls XYZ axes only: There's no spindle control; we touch off the zero position manually.

I've generated a toolpath with Fusion 360, for the pictured sample part.

The portion of interest is the mortise in the middle with 'dogbone' corners.  The corners are slightly larger diameter than my bit (straight-sided 3/16" diameter).

I'm using a pocket clearing operation, which steps down about 2mm per pass.  On each pass, it plunges downward in a helical path (near the right end), then traces narrow rectangle followed by an outer path which more closely follows the design profile.  After all passes are complete, there's a final finishing pass at full-depth (but only about 1/2mm bit engagement).

The pictures show my part, the toolpath, and the path actually followed by the machine.  The screenshots are from the Mach 4 computer attached to the machine, and clearly show that Mach 4 seems to be deliberately ignoring portions of my toolpath, though the initial preview of the toolpath appears correct!

The green lines are the preview, created by refreshing the display before running the job.  They match the path as generated in Fusion 360.

The white lines are traced during the job run.  They accurately reflect what the machine was doing.  Note that it 'cuts the corner' for the upper-left and lower-right corners of the 'outer' profile during each pass.

During the final 'finishing pass' it follows the toolpath properly... but since it hasn't done all the initial clearing, this seriously risks breaking the bit!  I'm lucky I got away with it.

Is there a configuration issue I should be looking at?    How can I troubleshoot further?


Re: Mach 4 not following toolpath
« Reply #1 on: November 13, 2018, 04:43:29 PM »
This might be happening because the acceleration values for the machine
configuration are causing excessive blending in corners while operating in
constant velocity mode. Try using exact stop mode or slow down the
cutting velocity to see if you get different results. Since you can see this
on screen, you could test while cutting air.
Steve Stallings
www.PMDX.com
Re: Mach 4 not following toolpath
« Reply #2 on: November 13, 2018, 04:51:43 PM »
Thanks for the suggestion.  I'll give it a shot & let you know.

Meanwhile, is there some documentation somewhere that covers the things you just mentioned? 

We have a lot of folks using this machine; some more sophisticated than others.  It's entirely possible that someone loused up the configuration.

Re: Mach 4 not following toolpath
« Reply #3 on: November 13, 2018, 05:35:46 PM »
You can use G61 in your program to force exact stop mode, i.e. no blending.

G64 will turn constant velocity back on.

You can configure the default mode using the screen at-   Config>Control  using the
General tab, look down the left side for Motion Mode.

Machine configuration of max allowed acceleration is on the pages at-  Config>Control
using the Motors tab. Hi-light the desired motor on the right side and then you can
edit the numbers in the Acceleration and Velocity numbers below. Be sure to write
down the current numbers before changing anything.

If you are running an older install of Mach4 you may need to look at-  Config>Mach
instead of-  Config>Control.
Steve Stallings
www.PMDX.com
Re: Mach 4 not following toolpath
« Reply #4 on: November 18, 2018, 04:04:54 PM »
Hey all,
Thanks to your help, I was able to successfully cut my parts... but I have questions.

The G61 (exact-stop mode) command did solve the problem, but at excessive cost in my opinion.
I could see the excessive accel/decel motion at every segment (just as cautioned in the G-code reference manual).

I could also solve it by slowing the motion down, but I had to slow down much more than I wanted to.  50 IPM got it close enough (though there was still _some_ corner cutting evident).

The job was initially set at 297 IPM, which, it turns out, is faster than our machine can go.  We have max speed at 190 IPM, max acceleration at 6 IPS^2.  This, because have a rather heavy X-carriage with two spindles.  We're going to be reconfiguring soon to single spindle & will probably change acceleration at that time.

Still, this behavior seems strange to me given the use case.  Note that my tool path has a 'cusp' at the corners of interest.  It's supposed to be a dog-bone, which is a fairly common technique.

I would think this angle too sharp for the constant-velocity logic to kick in.  I expect this kind of cornering logic to take effect only at corners with shallow angles, ...as produced by simple CAM packages that render short line segments to simulate an arc instead of rendering a G2 or G3 command, for instance.

Is there a way to program the 'turn-angle' at which the constant-velocity logic takes effect?

Re: Mach 4 not following toolpath
« Reply #5 on: November 18, 2018, 04:20:48 PM »
There is a way to set up an angle sensitive slow down in corners. You
can access it from the tab for Wizards at the top of the screen. Select
the "CV_Feedrate" from the resulting drop down window. There was a
description of how to use it here on the forum, but alas, search is not
currently working.
Steve Stallings
www.PMDX.com
Re: Mach 4 not following toolpath
« Reply #6 on: November 18, 2018, 04:30:18 PM »
Hi,
I am not familiar enough to offer any advice on the adjustments you can make to the CV tuning.

Quote
We have max speed at 190 IPM, max acceleration at 6 IPS^2.
There is your problem right there....that acceleration is way WAY too low. That's what causes the deviations that you have noted.
You can reduce the toolpath speed and you describe increasingly accurate results. This comes about because the max acceleration
becomes a significant fraction of your max velocity.

6/50=0.18 or 12%
6/190=0.031 0r 3.1%

You will get the same results at 190IPM as at 50IPM currently IF you can increase the acceleration to 12% of 190 ie 22.8 in/sec2.

CV is trying to make the best of your machine.......no doubt you could tune the CV feature to do a better job but you could address the underlying
problem......lack of acceleration.

Craig
'I enjoy sex at 73.....I live at 71 so its not too far to walk.'
Re: Mach 4 not following toolpath
« Reply #7 on: November 18, 2018, 05:15:54 PM »
Just did a bit of surfing, and found the following post.  It's a good read, though this discussion seems to be centered on Mach3:

http://forum.machsupport.com/forum/index.php/topic,33990.0.html
  Sounds like user 'ART' has explained the situation quite well.
  Mach4 does not seem to have the 'CV Dist Tolerance' and 'Stop CV Angles' settings.
  User DaveK0974 seems to have run into precisely the same problem I had with dog-bone corners.

I also read the referenced Mach3_CVSettings_V2.pdf.

From that, it looks like what I'm after is a Mach4 equivalent of Mach3's "CV Dist Tolerance" and "Stop CV on angles" settings.
Does such a setting exist somewhere?

Re: Mach 4 not following toolpath
« Reply #8 on: November 18, 2018, 05:21:12 PM »
> Does such a setting exist somewhere?
Ah, just saw the note about 'wizards' ...I'll look there.

And, yes, I figured our acceleration was way too slow too.  I'll take it up with our machine steward when we reconfigure (later this week).
..But I still think the angle limiting has merit.  I can't imagine a case for CV kicking in when turning more than 90 degrees, no matter _what_ the acceleration is set to.
« Last Edit: November 18, 2018, 05:28:10 PM by mkeveney »

Offline Mauri

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Re: Mach 4 not following toolpath
« Reply #9 on: November 18, 2018, 06:16:42 PM »
mkeveney,
Use the mcCvTurningWizardV3-3 BETA or any later version (it is located in the Wizard section and selected by WIZARD).
Depending on the type of machining select the appropriate Axis.
Use X/Y in the example you posted.
Use X/Y/Z in a 3D example.
Use X/Y/Z/A in a 4Axis example.
Select the Tolerance based on how good your CNC machine is (Accuracy including backlash) example .01mm.
Then process to update the Machine.ini.
I set a maximum CV Feed Rate of 150 on intricate 3D machining with .05mm TBN cutters.
Once you have the settings in place in Machine.ini (like example below) and CV is set to ON in Mach4, then you can test it by using Mach4 Simulation and view the profile verse the cut profile it they look close then you are good to go.
You can also test Lettering or Roadrunner in simulation.
You could automate all this if you do a little programing so you do not have to edit Machine.ini.
Regards,
Mauri.

Example settings for CV Feed Rate and CV Blend Radius below in Machine.ini

[CVFeedrate]
Angle_0=150.000000
Angle_1=150.000000
Angle_2=150.000000
Angle_3=150.000000
Angle_4=150.000000
Angle_5=150.000000
Angle_6=150.000000
Angle_7=150.000000
Angle_8=150.000000
Angle_9=150.000000
Angle_10=150.000000
Angle_11=150.000000
Angle_12=150.000000
Angle_13=150.000000
Angle_14=150.000000
Angle_15=150.000000
Angle_16=150.000000
Angle_17=150.000000
Angle_18=150.000000
Angle_19=150.000000
Angle_20=150.000000
Angle_21=150.000000
Angle_22=150.000000
Angle_23=150.000000
Angle_24=150.000000
Angle_25=127.000000
Angle_26=127.000000
Angle_27=127.000000
Angle_28=127.000000
Angle_29=127.000000
Angle_30=101.000000
Angle_31=101.000000
Angle_32=101.000000
Angle_33=101.000000
Angle_34=101.000000
Angle_35=101.000000
Angle_36=101.000000
Angle_37=76.000000
Angle_38=76.000000
Angle_39=76.000000
Angle_40=76.000000
Angle_41=76.000000
Angle_42=76.000000
Angle_43=76.000000
Angle_44=76.000000
Angle_45=76.000000
Angle_46=76.000000
Angle_47=76.000000
Angle_48=50.000000
Angle_49=50.000000
Angle_50=50.000000
Angle_51=50.000000
Angle_52=50.000000
Angle_53=50.000000
Angle_54=50.000000
Angle_55=50.000000
Angle_56=50.000000
Angle_57=50.000000
Angle_58=50.000000
Angle_59=50.000000
Angle_60=50.000000
Angle_61=50.000000
Angle_62=50.000000
Angle_63=50.000000
Angle_64=50.000000
Angle_65=50.000000
Angle_66=50.000000
Angle_67=50.000000
Angle_68=50.000000
Angle_69=25.000000
Angle_70=25.000000
Angle_71=25.000000
Angle_72=25.000000
Angle_73=25.000000
Angle_74=25.000000
Angle_75=25.000000
Angle_76=25.000000
Angle_77=25.000000
Angle_78=25.000000
Angle_79=25.000000
Angle_80=25.000000
Angle_81=25.000000
Angle_82=25.000000
Angle_83=25.000000
Angle_84=25.000000
Angle_85=25.000000
Angle_86=25.000000
Angle_87=25.000000
Angle_88=25.000000
Angle_89=25.000000
Angle_90=25.000000
Angle_91=25.000000
Angle_92=25.000000
Angle_93=25.000000
Angle_94=25.000000
Angle_95=25.000000
Angle_96=25.000000
Angle_97=25.000000
Angle_98=25.000000
Angle_99=25.000000
Angle_100=25.000000
Angle_101=25.000000
Angle_102=25.000000
Angle_103=25.000000
Angle_104=25.000000
Angle_105=25.000000
Angle_106=25.000000
Angle_107=25.000000
Angle_108=25.000000
Angle_109=25.000000
Angle_110=25.000000
Angle_111=25.000000
Angle_112=25.000000
Angle_113=25.000000
Angle_114=25.000000
Angle_115=0.000000
Angle_116=0.000000
Angle_117=0.000000
Angle_118=0.000000
Angle_119=0.000000
Angle_120=0.000000
Angle_121=0.000000
Angle_122=0.000000
Angle_123=0.000000
Angle_124=0.000000
Angle_125=0.000000
Angle_126=0.000000
Angle_127=0.000000
Angle_128=0.000000
Angle_129=0.000000
Angle_130=0.000000
Angle_131=0.000000
Angle_132=0.000000
Angle_133=0.000000
Angle_134=0.000000
Angle_135=0.000000
Angle_136=0.000000
Angle_137=0.000000
Angle_138=0.000000
Angle_139=0.000000
Angle_140=0.000000
Angle_141=0.000000
Angle_142=0.000000
Angle_143=0.000000
Angle_144=0.000000
Angle_145=0.000000
Angle_146=0.000000
Angle_147=0.000000
Angle_148=0.000000
Angle_149=0.000000
Angle_150=0.000000
Angle_151=0.000000
Angle_152=0.000000
Angle_153=0.000000
Angle_154=0.000000
Angle_155=0.000000
Angle_156=0.000000
Angle_157=0.000000
Angle_158=0.000000
Angle_159=0.000000
Angle_160=0.000000
Angle_161=0.000000
Angle_162=0.000000
Angle_163=0.000000
Angle_164=0.000000
Angle_165=0.000000
Angle_166=0.000000
Angle_167=0.000000
Angle_168=0.000000
Angle_169=0.000000
Angle_170=0.000000
Angle_171=0.000000
Angle_172=0.000000
Angle_173=0.000000
Angle_174=0.000000
Angle_175=0.000000
Angle_176=0.000000
Angle_177=0.000000
Angle_178=0.000000
Angle_179=0.000000



[CVBlendRadius]
Angle_1=26.524439
Angle_2=6.720417
Angle_3=2.986852
Angle_4=1.725206
Angle_5=1.075267
Angle_6=0.746713
Angle_7=0.578255
Angle_8=0.431301
Angle_9=0.345280
Angle_10=0.268817
Angle_11=0.234169
Angle_12=0.201911
Angle_13=0.172043
Angle_14=0.144564
Angle_15=0.119474
Angle_16=0.119474
Angle_17=0.096774
Angle_18=0.096774
Angle_19=0.076463
Angle_20=0.076463
Angle_21=0.076463
Angle_22=0.058542
Angle_23=0.058542
Angle_24=0.058542
Angle_25=0.043011
Angle_26=0.043011
Angle_27=0.043011
Angle_28=0.043011
Angle_29=0.043011
Angle_30=0.029869
Angle_31=0.029869
Angle_32=0.029869
Angle_33=0.029869
Angle_34=0.029869
Angle_35=0.029869
Angle_36=0.029869
Angle_37=0.019116
Angle_38=0.019116
Angle_39=0.019116
Angle_40=0.019116
Angle_41=0.019116
Angle_42=0.019116
Angle_43=0.019116
Angle_44=0.019116
Angle_45=0.019116
Angle_46=0.019116
Angle_47=0.019116
Angle_48=0.010753
Angle_49=0.010753
Angle_50=0.010753
Angle_51=0.010753
Angle_52=0.010753
Angle_53=0.010753
Angle_54=0.010753
Angle_55=0.010753
Angle_56=0.010753
Angle_57=0.010753
Angle_58=0.010753
Angle_59=0.010753
Angle_60=0.010753
Angle_61=0.010753
Angle_62=0.010753
Angle_63=0.010753
Angle_64=0.010753
Angle_65=0.010753
Angle_66=0.010753
Angle_67=0.010753
Angle_68=0.010753
Angle_69=0.004779
Angle_70=0.004779
Angle_71=0.004779
Angle_72=0.004779
Angle_73=0.004779
Angle_74=0.004779
Angle_75=0.004779
Angle_76=0.004779
Angle_77=0.004779
Angle_78=0.004779
Angle_79=0.004779
Angle_80=0.004779
Angle_81=0.004779
Angle_82=0.004779
Angle_83=0.004779
Angle_84=0.004779
Angle_85=0.004779
Angle_86=0.004779
Angle_87=0.004779
Angle_88=0.004779
Angle_89=0.004779
Angle_90=0.004779
Angle_91=0.004779
Angle_92=0.004779
Angle_93=0.004779
Angle_94=0.004779
Angle_95=0.004779
Angle_96=0.004779
Angle_97=0.004779
Angle_98=0.004779
Angle_99=0.004779
Angle_100=0.004779
Angle_101=0.004779
Angle_102=0.004779
Angle_103=0.004779
Angle_104=0.004779
Angle_105=0.004779
Angle_106=0.004779
Angle_107=0.004779
Angle_108=0.004779
Angle_109=0.004779
Angle_110=0.004779
Angle_111=0.004779
Angle_112=0.004779
Angle_113=0.004779
Angle_114=0.004779
Angle_115=0.001195
Angle_116=0.001195
Angle_117=0.001195
Angle_118=0.001195
Angle_119=0.001195
Angle_120=0.001195
Angle_121=0.001195
Angle_122=0.001195
Angle_123=0.001195
Angle_124=0.001195
Angle_125=0.001195
Angle_126=0.001195
Angle_127=0.001195
Angle_128=0.001195
Angle_129=0.001195
Angle_130=0.001195
Angle_131=0.001195
Angle_132=0.001195
Angle_133=0.001195
Angle_134=0.001195
Angle_135=0.001195
Angle_136=0.001195
Angle_137=0.001195
Angle_138=0.001195
Angle_139=0.001195
Angle_140=0.001195
Angle_141=0.001195
Angle_142=0.001195
Angle_143=0.001195
Angle_144=0.001195
Angle_145=0.001195
Angle_146=0.001195
Angle_147=0.001195
Angle_148=0.001195
Angle_149=0.001195
Angle_150=0.001195
Angle_151=0.001195
Angle_152=0.001195
Angle_153=0.001195
Angle_154=0.001195
Angle_155=0.001195
Angle_156=0.001195
Angle_157=0.001195
Angle_158=0.001195
Angle_159=0.001195
Angle_160=0.001195
Angle_161=0.001195
Angle_162=0.001195
Angle_163=0.001195
Angle_164=0.001195
Angle_165=0.001195
Angle_166=0.001195
Angle_167=0.001195
Angle_168=0.001195
Angle_169=0.001195
Angle_170=0.001195
Angle_171=0.001195
Angle_172=0.001195
Angle_173=0.001195
Angle_174=0.001195
Angle_175=0.001195
Angle_176=0.001195
Angle_177=0.001195
Angle_178=0.001195
Angle_179=0.001195
Angle_0=0.000000