Bit progressing in circle as spindle moves up and down

Got my x-carve up and running. Hoping someone could suggest help for a problem I’m having. As the spindle moves up and down, the bit is tracing out a circle in the x/y plane. Probably tracing out one full circle for each full rotation of the ACME Lead Screw.
I tried tightening the screws on the Delrin Nut, that didn’t seem to help.

I hope I’m just missing something stupid and obvious and someone can suggest how to fix my problem.


Mine was doing something similar (not exactly circles, but it was wobbling quite a lot). The culprit was not having my Z axis v-wheels tight enough to the makerslide. My suggestion is to take a look at your eccentric nuts on the Z and make sure they’re tight and that they’re putting enough pressure on the makerslide.

If it’s not that, then you might have a bent threaded rod.