The CNC lathe machine is machining inner holes, each finished workpiece’s sizes are different, and the finish is ellipse, not circular.

Check spindle motor vibration but it is fine, and the other machine is using the same CNC program and that is normal, so it is not CNC program problem neither.

Let the user to make another workpiece, then find out the clamping force is not enough for the workpiece, that is the reason of the problem, correct this then the machining sizes are normal.