Juddering...was working fine, now juddering like crazy

Mostly Printed CNC - MPCNC Troubleshooting
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I’ve spent the last week working on a large terrain carving (13" square, 3" deep) that’s required one roughing pass and two finishing passes (I do it a few hours at a time). The roughing and first finishing pass went fine, and the second finishing pass is about 2/3 done. All of a sudden, I noticed that the MPCNC was juddering and starting to go off-path, so I immediately shut it down.

Troubleshooting so far:

a) Cleaned rails, bearings (removed easily removable ones, brushed rest with a Dremel brass wire brush and compressed air; pretty sure there isn’t debris causing it). Reassembled.

b) Did concentric circles (2" stepdown in diameter) from 13" to 1"; judder fairly pronounced, but couldn’t tell if X or Y, so on to step (c).

c) Did concentric squares (same size/stepdown)–issue seems to only manifest on X-axis cuts (rapid traverses and Y-axis cuts don’t seem to have any issues). The X-axis cut juddering seems to happen mostly near the middle of the square edges closest to the X-axis (it doesn’t seem to happen near the square corners/closer to either Y rail). I think it’s arising in the far X-axis truck; the shuddering seems more pronounced there than on the near X-axis truck (with “near” being closest to home); this is based on how loud the chatter/judder is and the amount of vibration that I can feel when putting my hand on the trucks. It also seems to happen more when moving in +X direction than in the -X direction.

This is a Primo with 36" long 1" OD stainless rails and a fair amount of Z-axis travel (3" to 4"; needed due to the elevation in the carving); the controller is a Jackpot2 running FluidNC v3.9.9 and I’m using dual endstops. The Gcode is generated from ESTLCam.

Some videos:

Concentric Circle Test (very short).

Concentric Square Test (2.5 minutes; juddering happens at 2:17).

Actual carving part test (2 minutes; juddering happens at 1:30 and 1:50 to the end). This video has pretty extensive rapid moves that had no issues. I offset the cut path upward a millimeter or two to avoid actually hitting the wood.

I’m a little baffled since it was working just fine for the last two weeks as I’ve been whittling away at this a few hours a day, and now it’s developed this issue. It didn’t seem to have this problem with the first finishing pass (which was identical except that it also had the trench for the epoxy inlay and was a mm higher overall).

Any ideas? If all else fails, I might be able to relocate the part closer to the far X-axis rail; it seems like the judder doesn’t manifest there nearly as much. But I think getting it all lined up in the new location would be a challenge and I’d be likely to get a noticeable seam/transition line that I want to avoid.

Suggestions would be much appreciated…

Christian

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If you used stepper wire extendons, I would check the connections. Solder rhem if possible. Weak connections can cause so many intermittent issues.

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Agree with @larryk You have a wiring issue

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Hi Larry and Jonathan,

Thanks for the suggestion, I’ll look into that. You are correct that the stepper wires had to be extended, although every extension connection was soldered and heat-shrinked. Maybe I have a solder joint in the flexible cable tracks that failed; can’t remember where the solder joints ended up.

I’m curious why it doesn’t seem to be an issue during rapid traverses–I’d think there’d be juddering there as well since the cables are being exercised in the same way. Is it because the speed/momentum during rapid traverse bridges the gaps in continuity?

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I have experience this myself. I had it set up using the tape measure method. Fast moves rhe Y seemed to work but moving slow it vibtates in the same spot. My joint was right in the middle of the arc of tape . Careful checking showed that at faster speeds I sometimes could lose a few steps. I think maybe that momentem carries it past the missing coil pulse

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Re-wired the stepper extensions tonight, replaced with continuous wire through the flexible cable tracks. Seems to be working smoothly again–did my square and circle patterns with zero judder.

Thanks for pointing me down the right path, Larry and Jonathan, much appreciated!

Will see about finishing off my carving this weekend when I have a nice block of time.