Shapeoko Pro periodically stutters on y-axis

I have a Shapeoko Pro XXL. Sometimes when I am initializing the machine or even in mid-project, the CNC stutters fairly violently on the y-axis and looses tracking on where it is on the table. My CNC used began doing this only occasionally but has gotten more and more frequent to the point that I can’t cut anything now.

I’ve been unable to reach support today. I really need to get a project out. Any suggestions?

Thanks in advance for your help.


Could be a wiring problem - if you have a connector with an intermittent fault, you might be dropping one ‘phase’ of the motor.

You could set up a program that just moves back-and-forth on Y, and try manipulating each connector. If the problem gets better / worse at one particular connector, well there’s your problem.

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Please power down and remove (and inspect) both Y-axis belts — if they are in good condition, mark them so that when reinstalled they can be swapped end-for-end and side-for-side.

Check the pulley set screws:

and the wiring and connectors

If everything is in good condition and secure, power up, connect to the machine and try intializing — the machine should home the Z-axis as normal, and begin moving both X- and Y-axes — the X-axis should finish homing, while the Y-axis motors should turn until they time out — do they turn evenly and in synch?

If they do, re-install the belts and re-tension per the instructions and see:

If you continue to have difficulties, let us know what you found from the above at and we will do our best to assist.

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While you have the belts off, move the gantry back and forth, the same with the x axis. Check for any binding or grittiness of the carriages on the rails, clean and relubricate.


Thanks for the help! All of this sounds helpful. I will give this a go this evening and reach out if this doesn’t seem to remedy the problem.

I am crushed that the instructions do not show the witness mark. :laughing: :laughing:

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Adding a witness mark is a quick one-second check.


Good Luck


I had something like what you described happen toward the end of a job and then again when trying to re-initialize the machine after the incident. I shut down, powered back up and it initialized ok. I then shut down and checked belt tensions and found one had loosened up. I re-tensioned them and have not had the issue since. It could be as simple as the two y belts being significantly different tensions…Maybe…

While I was doing the re-tension I found that the clip for the belt that loosened up was a little under a 90 deg bend while all the others were slightly over 90 deg…like it was over-bent. I flexed it back open a bit and it seems to be holding tension now. It may be worth a check to see if belts loosened up and if so check the clips to be sure they are all bent the same amount and slightly more open than a 90 deg bend. Just my thoughts…


I appreciate all the help and suggestions. Glad to be connected to this community.

After I removed the y-belts last night, I noticed that the slider on the left rail wouldn’t move without considerable force. I couldn’t see any obstruction. I attempted to take the two-part slider apart, but even with all screws removed, it was still intact. I’m guessing some of those pieces either snap together or are glued. I used a rubber mallet and some lubrication (hope that doesn’t void any kind of warranty) and eventually got the sliders to move freely. I still can’t see any reason they wouldn’t move freely before. After replacing the y-belts, everything seemed to work perfectly.

Perhaps I had different tensions on the two belts and that somehow caused one set of sliders to bind? I don’t know.

Again, thanks for the assistance.


This turned out to be the problem! Thanks.


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