I just built my XXL, and while making my new wasteboard (drilling holes in it), I noticed that my Z axis carriage “wiggles” when it’s drilling. Here’s a video I posted of it on TikTok
https://www.tiktok.com/@martinstudio/video/6931894973155560710
Do I need to tighten the eccentric bolts more? I’m worried about the carriage binding… 
If the machine is mechanically sound, the toolpath workaround here is to machine a smaller hole in the center, then make a finishing pass around the perimeter.
Grab hold of you Z axis and and try to physically wiggle it. If it has wiggle then look at your V-wheels for tightness. If the axis does not wiggle then the motion I saw is as Will explained it is cutting around the center of the hole then a run around the outside. The Shapeoko will not drill 1/4 inch holes with a 1/4 inch bit. You have to trick the Shapeoko/CC by making the hole slightly larger than the bit. IF you make a 1/4 inch hole and pick the 1/4 inch bit you will not see the hole in the preview because CC will not allow that. So if you make the hole .252 CC will cut it but will make each depth of cut level in at least two passes, center and then around the outside of hole. From the video it looks like what Will and I have described. But check your Z axis for movement manually because both things can be true about your Z carriage.
Ok, I’ll head out there in a few minutes to manually wiggle it. How much engagement should I see on the V-wheels? Do I want them just about a thousandth shy of touching, so it still moves smoothly? Or do I want them to actually touch, even if it adds some drag to the carriage?
The holes are .3126 in diameter (using Myers Woodshop’s waste board plan, with some modifications). I’ll check the V-wheel engagement when I head out in a few minutes.
EDIT: Also, thanks!
So if your holes are round and .3126 there is likely nothing mechanically wrong. If your holes are egg shaped then it would be a mechanical issue with v wheels loose and/or loose set screws on axis stepper motor.
Are the holes round and the correct size?
@TheJesseJones You certainly want some engagement (touching) of the v-wheels to the rails. I like the simplified rule of:
If you can spin the v-wheel with one finger, tighten it juuuust until you are no longer able to spin it with one finger (even with friction). Once there, the entire carriage should smoothly move with the turning of the v-wheel.
You definitely want all the v-wheels to be touching or engaged on the rail. Winston has a great video about Squaring, Tramming, and Calibrating at 3:30 he talks about how to tell if the v-wheels are tightened correctly. (@dakyleman beat me to it.)
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