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PM-940 CNC Jumping With Gcode

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phazertwo

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Dec 31, 2016
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#1
Hi everyone. I bought a PM-940 cnc a few week or so ago and have been having trouble setting it up. I think I have about everything working (at least enough to run some gcode). However gcode seems to be the problem! I can jog the table and z all over the place, but if I turn control over to Mach3 it jumps every second or so. I can do a simple G0 move, or just tell it to go to zero. Either way it jumps.

IT has nothing to do with position, as I can change the speed of the motor and make it go a little further before it does it. It ALWAYS seems to do it about 1sec after I start the code.

For my settings please refer here http://www.hobby-machinist.com/threads/pm-940m-cnc-pre-assembled.49011/page-2

My settings are identical to Cut2cuts's. Since you cannot see the motor tuning section I am running 60ipm and 10in/sec/sec. And I have tried all the way up to 100/10 all the way down to 10/.5 and it still does it after about 1 min. BUT IT WORKS FINE IN JOG?

What am I missing here?

Edit: I should also add that when I am running very slowly (10 IPM) you can actually see the DRO stop as well, but it doesn't loose steps because it's moving so slow...

PZ
 
Last edited:

TomS

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May 20, 2013
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#2
I'll take a SWAG at this. Mach3 does a look ahead when running code. Could be the number of lines is set too low so it runs the line of code, then looks at the next line causing the machine to stop then start again. IIRC 20 line look ahead is where mine is set.

Hope this is it.

Tom S.
 

phazertwo

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Dec 31, 2016
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#3
CLOSE! It was the buffer time in the nMotion controller config. Looks like Cut2cut is running 759ms. Mine is currently up around 2000ms and seems to be working fine now. I'm not sure if there will be any adverse effects from running such a high buffer.

I'm also wondering if that has to do with the speed of my computer... which is slow.

PZ
 
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