yikes, one thing after another last week with my x carve. now that i have solved thx to the forum and tech support my y axis not moving issue and job and then job stopping issue, i now have a calibration issue. if i can draw a circle in the air accurately, but now when milling, is that most likely a belt issue or could it be I have the potentiometer set wrong on on of the axes?
An image of your carved circle would be very helpful 
However, if you design a perfect circle and it is carved as a perfect ellipse - then the X/Y isn’t calibrated properly or need micro stepping / step per mm adjustment.
If for instance the carved circle is flat on two sides or the “corners” are skewed you have one axis with slack.
An image would tell more
Thanks for your replies. I am still lost unfortunately as to the problem. I have rechecked belts and vwheels. I am never totally sure how they are to be calibrated though. The y axis belts are not slack but not ultra tight. all the v wheels are connected, I have tried loosening and tightening. sometimes the y jog works ok, but no what is happening is that the left side is sometimes binding, and will not move. i also noticed I can move the x axis by hand easily, but can’t budge the y axis by hand
I had a similar problem once . Acted like the left side was dragging or skipping once in a while. Turns out i had a bad spot on the motor wire. Right at a plug where the motor plugged in to the extension wire. I cut the plug out and soldered it and never had the problem again. Might check in the drag chain if you have one for a wire short. Or anywhere the wire might bend over and over.