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Oh I think I know who this is. Circles require all the axis gears to be meshed 100%. They also require the gantry to be square. If your machine has any play in any of the axis with power on to the motors (this keeps the motors from moving as the power freezes them in place) then it can be a loose setscrew or gear not fully engaging. These machines make ultra round circles when they are set. Power up your controller and press you power button to lock the motors. Then go around to each of the 3 X,Y and A axis and see it they wiggle. If they do you will need to loosen the 3/8 nuts and push the gear into the rack and re-tighten. If you ran off the gear rack and pushed just one side on it could tweak the gantry over time of running then you will need to re-square the gantry with the end stops.
The other thing that can affect roundness is having your cut height too high. This means your cut height lowers after THC delay is ended and tip volts takes over the cut height when its already cutting the diameter.