Choppy tool path

14 May 2018 17:36 #110734 by allenwg2005
allenwg2005 created the topic: Choppy tool path
I hope this is the proper place for this question. (If not I apologize).

I have Some ugly tool paths, it's been years since I set this up, (I have just put up with it all this time).
As I recall I did the best I could back then, I would like to address it now.
Can someone please point me to a specific area in the manual that would affect this sort of thing saving me time digging through the entire process?

Thanks in advance
14 May 2018 19:07 #110735 by Todd Zuercher
Todd Zuercher replied the topic: Choppy tool path
Could you better describe your problem, or post a picture that shows the problem you are trying to describe?

"Ugly tool paths", or "Choppy tool path" doesn't tell us much.
14 May 2018 22:31 #110745 by allenwg2005
allenwg2005 replied the topic: Choppy tool path
Hi Todd,

I looked around for an example to photograph and I really don't have a good one at the moment (I just cleaned out a bunch as fate would have it).

What is happening is on straight lines it is leaving a smooth clean cut (wood and aluminum), on angles and arches it leaves facets, like an arch with too few lines making up the curve.

I hope that helps, I'll keep looking for on example if this dosen't get it.

Thanks, Allen
15 May 2018 12:28 #110760 by Todd Zuercher
Todd Zuercher replied the topic: Choppy tool path
Ah, yes I am well familiar with such a problem. It is most likely not a Linuxcnc problem. But I'll do my best to help you mitigate it.

I'll need some more info about the machine. What type of drive system does it have? (motors, screws, racks...)

How good is the structure of the machine? What type of machine is it?

This type of problem is most often caused by physical deficiencies in the machines drive systems. Most commonly problems with a rack and pinion drive.
15 May 2018 15:58 #110769 by allenwg2005
allenwg2005 replied the topic: Choppy tool path
It's an old (20 years) oddly built gantry, it runs Anaheim steppers and drive (I know you are way familiar with those), and lead screws with recirculating ball nuts.

I've long suspected the way the machine was built being the issue.
You have confirmed my suspicions, as much as I'd love to address it I need to stay focused on other things right now.
I figured if it was a "Configuration" thing I could simply adjust it and that would be easy enough to do.
My idea to fix it would require a lot of time, parts, and materials.
Time being the real stumbling block at the moment.

Thanks again, Allen
15 May 2018 16:30 - 15 May 2018 16:32 #110770 by Todd Zuercher
Todd Zuercher replied the topic: Choppy tool path
If the machine used servos, it could have been a tuning issue, but since it is steppers, that means it is almost certainly a mechanical problem.

Something is causing one of the axis to move in a jerky rather than smooth fashion.

I have to maintain two large moving gantry routers at work that run Fanuc controls. And when they start doing this, it is usually one or more bad bearings on their pinion shafts, or the intermediate shaft for the belt reduction that drive the gantry.

The light duty routers we have that use Anaheim stepper drives, have rack and pinion drives, and when the pinion gears get worn out they exhibit this behavior.

If your machine dosen't use rack and pinion, look at things like worn/misaligned couplers, end support bearings, worn, over tightened or misaligned belt drive, or a bent or misaligned ball screw (or lead screw). It doesn't take much of a vibration to cause a big problem, especially on a machine with poor rigidity.
Last Edit: 15 May 2018 16:32 by Todd Zuercher.
15 May 2018 16:40 #110771 by allenwg2005
allenwg2005 replied the topic: Choppy tool path
As I read your suggestions I was recalling I had to replace two couplers when I got the machine, and now that I think of it I replaced a bad ball nut too, all reasons they dump the machine I'm sure.
I think I had better take a closer look at what I did to make sure I reassembled those properly.

18 May 2018 21:37 #110853 by andypugh
andypugh replied the topic: Choppy tool path
Just one other thing, check that the G-code looks smooth in the preview. It is just possible that the CAM package was running with a real coarse mesh. Or the input was really coarse STL.
The following user(s) said Thank You: allenwg2005
19 May 2018 14:33 #110884 by allenwg2005
allenwg2005 replied the topic: Choppy tool path
Thanks again Andy.
The preview looks real smooth, I am pretty sure this is my X-Y axis needing some attention.
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