My circles are lemons (machine problem) SO3

My machine cuts circles as lemons; I can’t figure out how to fix this problem.

Lemons consistently point in one direction or the other depending on cut type. (inside/outside cuts)


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I have tried:
-Adjusting belts
-tightening and adjusting several parts of the machine
-calibrating x and y
-changing materials, changing feeds and speeds
-different work holding methods
-a variety of end mill sizes, flutes, brands
-running old files that didn’t have this issue (they do now)

I’ve gotten it to the point where I can cut perfect squares, but my circles still come out as ovals/lemons, and my curves distorted. The squares really do come out with the side being the same length. The only thing I can think to blame at this point is the z axis plate which seems to be pushed back and forth (y axis)

If anyone has an idea how I can strengthen my axis (without getting a whole new system) or any other fix to this issue, please help.

That’s backlash. You have a pulley on X or Y that is loose - the axle is turning a little (about the distance of the flat on the axle) before the pulley starts turning. If everything was oblong in the same direction (no points) that would be x/y belt calibration or machine squaring.


Please check the pulley set screws:

and make sure the belt tension is appropriate:


UPDATE: One of my motors is not working.

When I turn the machine on and let it sit for a while, I can feel the other three motors are warm, one of them is not however. I opened up the back panel and everything seems to be connected just fine. I think my motor is dead.

Usually it’s a blown stepper driver — we have instructions for testing the components at:

Please test the various components and let us know at and we’ll do our best to help you sort this out.


Also check the cables and extensions, some people have had problems with the cables themselves pulling apart.

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