Posting this in case anyone else finds it of use -
So I’ve eventually solved the weird regular ‘wonky circles’ and presumed sticky x-axis issues - they were both manifestations of having an x pulley that had a small amount of play on the motor shaft.
I finally singled the cause down to this by printing a 100mm single layer square - and getting the regular ‘skip’ pattern of lines along the left and right sides and triangles on the top/bottom sides as shown in the picture. (the x-axis going from left to right).
You can find the stl for the 100mm square test print here - https://github.com/einon/shapes/blob/master/100mm_1layer_square.stl
