ok this makes no sense but apparently the htd 5m belt linking the stepper to the x axis was worn enough that it wasn’t acting as a timing belt, more like a tire.
it wasn’t JUST skipping steps, it was freely walking over the teeth and not using them at all. no only was it a small scale error, there was no bumping in its raster where it jumped a tooth, and it was so repeatable that a vector ruler followed by a 1000mm/s raster didn’t screw up or misalign the raster in any way and a second pass at the same job landed the ruler’s vertical ticks in the exact dame place. all while acting like a tire and not a timing belt
and i had that belt off last night. it appeared somewhat worn but not that bad i had ordered a spare awhile ago but found it needed 12mm wide and I had gotten a 15mm. well, sat down with a good pair of scissors and that 15mm belt now identifies as a 12mm. fixed all the probs
crazy!