Jitter issue - jagged circle

Hi, could anyone let me know what might be causing this? I carve a circle as a simple test, but it is jagged. The spindle and controller are on different circuits. I don’t know what else could cause this. Thanks in advance!

I am using 1/4" downcut spiral bit.

My initial thought was that it was due to inadequate clamping and the part shifting, but this does not appear to be the case after watching the video. Can you also post the source of the geometry file, and the G-code? This may provide more insight into why this happened.

Here’s the files:


This looks like an issue with one of the Y-axis motors or shaft couplings. One of your motors is not turning the ball screw, and the entire axis is being moved by the other motor.

Are both y axis motors powered on? The power connectors inside of one of the motors could be loose.

This could also indicate a shaft coupler that is slipping.

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I can’t open the .ART filetype, so I don’t know what the base geometry looks like. But I’m guessing it’s not a true CAD circle based on your g-code. By contrast, here is a 3.0" circle done in a CAD program, and programmed in Estlcam. It uses a .250 cutter with 3 cuts @ .125" deep. Your code is a rather large series of X-Y moves with no circular interpolation. You should try this program and see what happens.

I can’t agree with @DCK 's comment because the cuts in your picture have no evidence of anything but 3 identical passes, which would not be the case if it was an issue with the Y axis.

3.0 CIRCLE.nc (766 Bytes)

(Project 3.0 CIRCLE)
(Created by Estlcam version 11 build 11.245)
(Machining time about 00:00:50 hours)

(Required tools:)
(.250 EM)
M03 S12000
G00 Z2.0320

(No. 1: Part 1)
G00 X-29.6321 Y-28.7332
G00 Z0.5000
G01 Z0.0000 F127 S12000
G01 Z-3.1750
G02 X-10.0676 Y40.0287 I29.6321 J28.7332 F1016
G02 X39.6997 Y-11.2955 I10.0676 J-40.0287
G02 X-29.6321 Y-28.7332 I-39.6997 J11.2955
G01 Z-6.3500 F127
G02 X-10.0676 Y40.0287 I29.6321 J28.7332 F1016
G02 X39.6997 Y-11.2955 I10.0676 J-40.0287
G02 X-29.6321 Y-28.7332 I-39.6997 J11.2955
G01 Z-9.5250 F127
G02 X-10.0676 Y40.0287 I29.6321 J28.7332 F1016
G02 X39.6997 Y-11.2955 I10.0676 J-40.0287
G02 X-29.6321 Y-28.7332 I-39.6997 J11.2955
G00 Z2.0320
G00 X0.0000 Y0.0000


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I’m in agreement with Bill, I don’t see any shifting of your piece on the wasteboard and the pattern is being reproduced identically on each pass, so your machine is doing exactly what it is being told to do. So your problem is in the program. As for that, I’m not sufficiently knowledgeable to spot where that diffiency is but I’m certain you’ll hear from someone who is in short order.

Thanks for everyone’s responses so far!

I tried running your file @Machinist and was hopeful it was such a simple fix as using a different file type, however sadly I got the same result

Oddly, the imperfections seems to be in very similar positions as the other run.

As far as a potential motor issues, both Y-axis motors are powered on and seem to be operating correctly. I will look more into potential shaft coupler slippage…

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This geometry is typical of lost motion if the commanded path is a circle. In this case, both X and Y axes have lost motion as the path error appears on four sides. Check for looseness in mechanical couplings, thrust bearings, etc. Often the looseness is easily felt and spotted by firmly grasping the X carriage and/or Y gantry and shaking them back and forth.

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Everything seems pretty solid. However, I believe I have discovered the error of my ways. I removed the red pieces from the motors :clown_face:

In retrospect, I obviously should have thought more about removing those because there’s gaps without it. Pretty sure I threw them away, I’ll have to figure out how to replace them.

Edit for once, my hoarding tendencies pay off! I have the pieces, I am re-assembling now and hopefully the next test will be good!


That’ll do it! Good to hear you have it sorted!

Sadly, I could only find 2 out of 3 of the pieces (do they have a name?)

However, after placing them back into both the y-axis motors, 2 of the “corners” are gone from the circle! So I am confident that replacing the last one on the x-axis motor will fix the whole thing.

Thanks everyone!

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Hey Jonathan,

you can buy them here: coupler

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I’d call that part an elastomer coupling insert.


I found the couplers on the onefinity page… just a few bucks for the whole coupler (even though I just need the insert), but 19 bucks for shipping! Ouch… could be worse though


Excellent, so glad to hear you got it sorted! Yes, the elastomer insert is a very key piece of the couplers (as you found out). They help with shaft alignment & vibration. And without them… well, you’ve seen first-hand the result.

We are all here to learn & share this journey, and you’ll be making perfect circles in no time! :sunglasses:

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For science! New coupler came in today (all I needed was the insert). Thanks again everyone.


Hey Jonathan, hey all,

sometimes it’s good to read the fine manual :wink:

– Source: Onefinity Elite Series Setup Manual


I don’t know… The warning is only half the page, maybe it could be a bit bigger :rofl:


lol. Just proves you are not the only one :slight_smile: