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Author Topic: Stepping problems with slow feed rates.. Help!  (Read 4372 times)

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Stepping problems with slow feed rates.. Help!
« on: January 26, 2006, 02:21:05 PM »
Hi everyone,

I am new guy here, and I have a frustrating problem.  I am setting up a Taig cnc mill (for the University of Washington), with 1.8 degree stepper motors, being driven by a Deep Groove motor controller.  I have the mill calibrated reasonably well, but whenever I run a g-code file, or input code by hand on the MDI screen of Mach 3 which has a move of type G1, G2 or G3 and the feed rate is between 3.0 and around 8.0, my motors stall eventually and start missing steps.  I have optimized XP according to the docs, double checked that enhanced pulsing is on (and tried it off), switched into and out of Sherline mode, inverted pins, changed and changed acceleration and velocity settings, changed pulse width settings, etc.. basically I have tried everything I have heard suggested in the forums.  Ugh.  The waveform in the driver test is perfect, a smooth straight line and the diagnostics screen shows Mach 3 outputting 24050 pulses.

If I run a rapid feed move of G0 I have no problems.  Once the motors begin missing steps the accuracy is shot, and run is over..

Any ideas?  Thanks a million.   

Peter

Art

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Re: Stepping problems with slow feed rates.. Help!
« Reply #1 on: January 26, 2006, 02:51:07 PM »
Hi Peter:

  Try slowing the acceleration way down, just as a test. Does that stop it from occuring? How about pulse width, does increasing it do anything. This points towards a printer cabel that is a bit capacitive or something..

Art
Re: Stepping problems with slow feed rates.. Help!
« Reply #2 on: January 31, 2006, 04:48:25 PM »
Hi again,

thanks for the idea, I finally got a chance to work with the Taig again today, and even with really slow acceleration rates the motors stall.  It actually seems to me that they are stalling during the acceleration.  I have been running the spiral g-code test, as referenced in the Mach 3 User PDF, with various feed rates and regardless of the acceleration settings (0.01 - 4.0) the motors (primarily the Y and Z) catch and mis-steps while accelerating.

Oh, and I have tried various pulse width settings, from 0 to 14 (as high as the Step Pulse and Dir Pulse input boxes would allow), with any and all combinations in between, but nothing seems to change.

How can I diagnose if my printer cable is out of wack?

Thanks for the help, any suggestions at this point are appreciated!

Peter
« Last Edit: January 31, 2006, 04:51:24 PM by dx_artist »

Art

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Re: Stepping problems with slow feed rates.. Help!
« Reply #3 on: January 31, 2006, 05:58:03 PM »
Peter:

 Sonds more likely its your timng. Have you run the driver test? Does it have a good waveform?

Art
Re: Stepping problems with slow feed rates.. Help!
« Reply #4 on: January 31, 2006, 06:47:36 PM »
Hi Art,

Yes, I have run the driver test a bunch, and every time the waveform is an almost perfectly straight line.  Hmm.  If I run it for long periods of time I don't see any spikes as I have seen on my home laptop.  I have even run through every step on the XP optimise text.  The machine I am using is desktop P4 1.4 ghz, with 512 ram, and a clean install of XP pro.

Is it possible that the driver box is not supplying enough current?  The motors are 1.8 degree/step, 220 oz. steppers.  I don't know how to test for that...

Thanks again,

Peter
Re: Stepping problems with slow feed rates.. Help!
« Reply #5 on: February 01, 2006, 06:41:52 AM »
Under the  ports and pins check "Sherline 1/2 Pulse Mode" mode  and you should be good to go :)
Fixing problems one post at a time ;)

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