hi,
I am still waiting for my UM but I have a good experience with cnc.
Verify if the non-roundness is the same if you print on different place of the base, verify if there is non-roundness also in multiply of the measure you told (15-30-45), verify again if the calibration (mm/step) is correct at different scale objects, verify if the mechanical movement is fluid. at the end you could think about swapping the x and the Y motors to see if the squashing is changing axis, try to plot different gcode ( I mean use a pen and not the PLA/ABS) and use simple gcode for different shapes of different sizes. (a simple mach 3 demo could be useful to obtain the gcode)
last but not least: good luck!
Come on delivery boy...I'm waiting and I'm starting to be nervous... :lol: