Belt tension on Shapeoko XXL

I’m starting to see play in my cnc projects. Especially on profile cutting. I see that each pass is slightly misaligned to the last. Primarily left to right. It’s more pronounced on the larger projects 30" wide. So my question is do I tighten up the existing belts which appear to be in good condition, but have some side to side play. I’ve had the machine for 8 months with pretty much daily use. I dont see any visible wear spots or distortion in them. Looking for some advice / direction on this matter.



If your circles are not circles check your v-wheels. The belts could cause the issue if they are loose enough but if they are that loose it would be skipping steps.

To check your v-wheel only the bottom ones are adjustable. move your z carriage to the center of the gantry and push on one (of two) bottom v-wheels and the carriage should move and the v-wheel should not slip. Do this with both wheels.

Then check your v-wheels on the left and right but pushing on the v-wheels and the carriage should move and the v-wheel should not slip.

If you need to adjust the v-wheel insert an allen wrench and slightly loosen the bolt. Then put a wrench on your eccentric nut and adjust until the v-wheel is snug. Hold the wrench and tighten the allen bolt, if you do not hold the eccentric nut the torque of tightening will tighten the eccentric too much. After adjustment check as above. The wheels should feel snug but not so tight you put the v-wheels in a bind.

An alternate way is to grab the z axis and try to pull it up and down and it should not wiggle. Same for the Y plates. If the plates/z axis wiggle the v-wheels are likely loose.

The reason I think it is the v-wheels is when making a circle the forces of cutting the wood will make loose v-sheels ride up on the gantry/Y rails misaliging the router making less than perfect circles.

If you get perfect ovals consistently then you may need to calibrate the stepper motors. That is unlikely but possible. However you will get perfectly aligned ovals if the stepper motors need calibrating and not inconsistent or wavy lines in the circle.

Thanks for the help Guy! I’m working with your suggestion and checking what mentioned this afternoon. Hoping for great results…
Take care,


Thanks William for your response and information forwarded! I’m working with your information on the machine this afternoon along with some direction from Guy. Hoping everything comes together…

Take care,


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