Choppy motion - VCarve?

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MSimeone
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Choppy motion - VCarve?

Post by MSimeone »

Hi All,
I'll preface this by saying that I'm not sure if this is an Acorn issue, a Vectric issue, etc... Hoping for any enlightenment.
Ran my first "air cut" program today since commissioning my retrofit AXYZ 4010. I am a cabinet maker who also does furniture and some millwork. Not a CNC expert, but it is invaluable in my workflow.
Hardware specs are: AXYZ 4010 retrofit (dual R&P X, R&P Y, ballscrew Z, 5' x 10' bed). Centroid Acorn / C86ACCP. Teknic ClearPath. Servos were tuned by Teknic. All jog movements are precise and silky smooth.
For 99% of my work, I use Vectric V-Carve Pro. It is limited but generally simple and well suited for most woodworking applications. I made a simple program to run today, just to make sure everything went as planned as far as overall behavior. I used Vectric's Centroid (inch) post processor. Overall the post processor seemed to play nice. Everything was running at 300IPM, well under the 1200IPM that the Teknic technicians said to limit it to after running all of their tuning.
The primary issue I am having - smaller diameter circles cause faintly 'choppy' movement. I'm not sure it would be visible on camera or I'd try to get video.
Movement in every axis is silky smooth. Straight line along any axis, diagonals, corners, changes in direction, etc. Large diameter (30") circles are likewise silky smooth. Run some 6" diameter circles, however, and the machine has a faint choppiness. You can barely see it, but you can definitely feel it if you put your hand on the gantry, for instance.
My gut feeling - something about the way Vectric "draws" circles / the way Acorn interprets those circles? Like, maybe they are just a bunch of small lines? Is there a "smoothing" option I don't know about in either Vectric or Centroid? Has anyone else experienced anything like this?
I don't have access to the GCode right now - it's at the shop. I can post the code, or a report, or anything else necessary tomorrow morning when I get to the shop. Just hoping someone has some insight into this.
Thanks in advance!
Mike
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Re: Choppy motion - VCarve?

Post by RogDC »

Check out sword's post on smoothing it may help https://centroidcncforum.com/viewtopic. ... 541#p22541

Two things to be aware of on VCP and Aspire- try to keep your work area as small as possible when laying out vectors/3D, and use a higher resolution for the modeling when you start the job layout. Once you start off with 'standard' resolution, you won't be able to change it to 'high' resolution. If your work piece is 2'x 4', lay it out the size of the material, not the size of the machine.
ShawnM
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Re: Choppy motion - VCarve?

Post by ShawnM »

I also use Vcarve Pro and have Clearpath servos on an industrial grade Holz-Her router that I retrofit. I don't have the issues you do. I cut 1/8" thick aluminum sheets with my machine with dozens of 1/2" holes and smaller all day long and they are silky smooth. For standard geometry consisting of lines and arcs you don't typically use smoothing. For 3D surfacing or actual V carved files then you use smoothing. Vectric draws circles as four arcs, not a bunch of small lines, so there will be four nodes. If you "import" a DXF, DWG or a raster file from another program a circle may be imported as thousands of little lines but you can fix that in Vcarve.

Do you have any measurable backlash from the rack and pinions? Unless they are helical you probably do.

Did you read the smoothing manual?
https://www.centroidcnc.com/centroid_di ... manual.pdf
Last edited by ShawnM on Wed Feb 08, 2023 12:48 pm, edited 1 time in total.
MSimeone
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Re: Choppy motion - VCarve?

Post by MSimeone »

Shawn and Ron,
Thank you both for your replies so far. I'm heading to the shop in a little bit. When I get there, I'll inspect the code as closely as I'm able, as well as the actual vector drawings themselves. I think maybe programming a few circles in either the MDI or intercon may provide some insight? Maybe take the Vectric variable out of it?
I don't think the problem would be related to R&P backlash. The machine ran fine with it's previous control and motion suite (steppers, and the stock AXYZ AMC control). When I did the retrofit I also bought new bearing blocks, pinion gears, and drive belts straight from AXYZ. Thanks.
Mike
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Re: Choppy motion - VCarve?

Post by Gary Campbell »

You may simply be setting the feedrate or acceleration too high for that diameter. At the quarter points of a circle the machine must stop one axis and reverse its direction. At the eighth points there are individual axis feedrate changes.

If settings are too aggressive, then there may be a noticeable studder when either occurs. If there is any visible chatter or a divot in the cut path, then there is a mechanical looseness that will exacerbate the issue. Always eliminate the mechanical issues first.
I don't think the problem would be related to R&P backlash. The machine ran fine with it's previous control and motion suite (steppers, and the stock AXYZ AMC control). When I did the retrofit I also bought new bearing blocks, pinion gears, and drive belts straight from AXYZ.
When troubleshooting, do not take anything for granted. Look at everything, not just the things you think it could be, do not accept the things you have recently done as not part of the problem.
GCnC Control
CNC Control & Retrofits
https://www.youtube.com/user/Islaww1/videos
MSimeone
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Re: Choppy motion - VCarve?

Post by MSimeone »

Gary Campbell wrote: Wed Feb 08, 2023 9:49 am You may simply be setting the feedrate or acceleration too high for that diameter. At the quarter points of a circle the machine must stop one axis and reverse its direction. At the eighth points there are individual axis feedrate changes.

If settings are too aggressive, then there may be a noticeable studder when either occurs. If there is any visible chatter or a divot in the cut path, then there is a mechanical looseness that will exacerbate the issue. Always eliminate the mechanical issues first.
I don't think the problem would be related to R&P backlash. The machine ran fine with it's previous control and motion suite (steppers, and the stock AXYZ AMC control). When I did the retrofit I also bought new bearing blocks, pinion gears, and drive belts straight from AXYZ.
When troubleshooting, do not take anything for granted. Look at everything, not just the things you think it could be, do not accept the things you have recently done as not part of the problem.
Thank you Gary. I'll check the acceleration as well. Good point on the mechanicals. Do you have a fairly reliable method of testing for mechanical error?
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Re: Choppy motion - VCarve?

Post by Sword »

Take a look at the the circle in VCarve with the node editing tool, and see if it shows only 4 nodes/4 arcs or if it has many nodes all the way around. Also, check your g-code to see if it is using G2/G3 arcs or all G1 segments for the circle.
Scott
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Re: Choppy motion - VCarve?

Post by cnckeith »

post a fresh report.zip and the offending g code program and create a photo album of the machine tool and control box, post link here so we can see what you see. https://centroidcncforum.com/viewtopic.php?f=60&t=1043
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
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Re: Choppy motion - VCarve?

Post by MSimeone »

Scott,
I checked the vectors. They only have the 4 nodes. All commands are indeed G2/G3 commands.
Gary,
I measured backlash with a Mitutoyo indicator on a mag stand. I get a repeatable "0" on the long dual driven axis, and a repeatable .0005 on the gantry axis.
I also slowed accel considerable, no difference. I also slowed feedrates considerably, no difference.
I am starting to suspect the issue is in the motor tuning. It took Teknic a couple of tries to get it right initially, and now that I think about it, my test movement program that they used to tune was all straight lines (think a box with an 'x' in the center).
Thank you all for your input so far, I very much appreciate your insight.
MSimeone
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Re: Choppy motion - VCarve?

Post by MSimeone »

cnckeith wrote: Wed Feb 08, 2023 3:16 pm post a fresh report.zip and the offending g code program and create a photo album of the machine tool and control box, post link here so we can see what you see. https://centroidcncforum.com/viewtopic.php?f=60&t=1043
Hi Keith,
I'll do my best on getting some pictures. For now here are the report and the g code files. I am, however, leaning more and more toward a motor tuning issue. Thanks for your input and patience.
Mike
Attachments
circtest.cnc
(12.41 KiB) Downloaded 7 times
Profile 1.cnc
(117.75 KiB) Downloaded 4 times
report_184516E7DBBF-1215215449_2023-02-06_17-07-18.zip
(631.42 KiB) Downloaded 3 times
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