Had a quick look through the code and it moves the cutter around a 36mm square, cleaning out the interior of the pocket. So the resulting pocket should measure 36+cutter dia. So it sounds like the steps/per is wrong, or it's missing steps. If the pocket is accurately square, it is unlikely to be missing exactly the same number of steps on each axis, and the pocket sides would be stepped as it loses more and more steps on each depth pass. So it's looking like steps/per is wrong...

My best guess, anyway - but this is all long-distance diagnosis so could have missed something!

- Brian