Pockets and Grooves not milling correctly

For some reason, I’ve been struggling with my Shapeoko since right around the Christmas rush for my shop. I have been trying to mill some pockets in maple, which I have done hundreds of times before, and am seeing some very strange results where grooves are not being milled straight, and the machine seems to be tailing off when cutting pockets. So far, I’ve squared the machine, checked tension on all belts, adjusted wheels, and thoroughly cleaned all tracks. I have two examples to provide and really hope someone can help!

First, on some of the games I do, I simply mill a 1/8" groove over and over for game pieces to fit in to. I do three boards at at time on my CNC. You’ll notice that on the first board, the grooves are milled at weird angles and not straight, but farther down on the second and third boards, the grooves are fine.

I don’t know what would cause this to not work properly on the first board, but then work fine the rest of the way down? No idea what to look at to try and fix.

The other issue is when I am cutting pockets to store game pieces in the back of a board.

It seems that the bit is not hitting same spot as it goes through the cut cycles, resulting in ridges and totally off center cuts compared to a normal cut.

Normal pocket

Pocket not right

Ridges in pocket

Again, not sure what would cause this in just one of the three boards it’s cutting pockets in.

Any help would be tremendously appreciated!!


Have you checked the pulleys on the stepper motors? Try adding a witness mark on all the pulleys, and see if anything shifts during a cut.


I’ve never done that. I’m assuming just a vertical line when the pulleys are stopped, and then all the lines should be the same alignment when the cut is done?

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Yes, exactly. If anything is out of line, it indicates the pulley is not properly secured. If the screws are slightly loose, then the pulley could swing back and forth on the shaft, possibly sometimes jamming at one end of the swing or the other. This could explain why it sometimes works - the pulley is jammed tightly enough it doesn’t swing back.

So, even if you check it by hand, it might feel like it’s secure, but it’s not really.

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I tightened the pulley screws and noticed there was a tiny bit of play in a couple of them. Very small allen wrench, so I don’t know if I got enough torque.

Will be cutting pockets in 16 of my board games today. Wish me luck! Will report back afterwards.

Put a witness mark on the shaft/pulleys and always check them before and after cutting per:


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