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Jerky Motion?
« on: September 19, 2008, 02:41:17 AM »
I have had my mill up and running for about 6 months now and would like to resolve a problem that has bugged me finally to a point where I want to take care of it.  The mill seems to run jerky most of the time.  I think it is something that Mach is doing because it is smooth consistently on some parts, but jerky on others. 
I have included a link to a video of my machine running.  In the beginning of the video you will notice how jerky it is, and at the end of the video it is running pretty smooth.  What I have observed is that when cutting the inside corners, it is jerky, and when cutting outside corners it is smooth.  That does not make much sense to me as to why it is doing that.   I have also observed it is very jerky when cutting circles out.  The object that it is cutting in the videos had some circles that it cut out.  It was very jerky until about the 5th step over and it went smooth, and then on the 6th step over it was jerky again, but it acted this way on all 6 of the holes it made.  It seems like maybe I am missing something simple here?
I have checked and my CV mode is turned on.

On another note, when I am running in a parallel finishing mode, it runs real smooth and the Z axis seems to move up and down around humps perfectly smooth at speeds of 180ipm.

Video – High Res
http://www.saberfire.com/milling/mill1.mp4

Video – Low Res
http://www.saberfire.com/milling/mill2.mp4

Video – Lowest Res
http://www.youtube.com/watch?v=g25LTaqDCSA

Cut File
http://www.saberfire.com/milling/Antlers.zip


Here is a little about my machine…
It is a home built off of “Joes CNC 4x4”  I have done some mods, so it looks a little different, but still runs the same. 
300oz Hobby CNC Motors and Control Board running off of dedicated P4 2.4Ghz machine. 
Mach 3 Version 2.63
RhinoCam to generate Mach 3 Gcode

Offline Hood

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Re: Jerky Motion?
« Reply #1 on: September 19, 2008, 02:54:21 AM »
Turn off the CV Distance tollerence and Stop  CV on angles and see if that makes a difference. You will find them on the General Config page.
Hood
Re: Jerky Motion?
« Reply #2 on: September 19, 2008, 03:47:48 AM »
Wow!  Very smooth now, but now it might have caused a similar, smaller problem, it seems to not decelerate the motor when changing the direction, so it is a bit jerky on radical changes?  Do I need to increase my acceleration/deceleration  under the motor config, or will that not do anything if I am in CV mode?

Thanks,
Bob

Offline Hood

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Re: Jerky Motion?
« Reply #3 on: September 19, 2008, 04:18:42 AM »
Might help to lower the acceleration a bit, especially if your router is fairly fast but with light construction. Another thing you can try is enabling the CV settings again and messing with the distance to see what suits your machine.
Hood
Re: Jerky Motion?
« Reply #4 on: September 19, 2008, 08:11:14 AM »
bbristow,
Just in case you haven't seen this, it's a good description of how the CV setting can be utilized to get the best performance out of your machine.

http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

RC