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.

Bill

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.