Thanks for the feedback. We went ahead and bought the Shark. It's not especially fast and information from photo Vcarve computes differently. For example, a 12% step on the Shark (processed with the Shark controller) produces a different result compared to a 12% step on our kit built machine (processed with Mach 3).
I would have thought it would be uniform but it is definitely not. I guess there's always an experimentation process with settings?
This experience with a new machine and controller has given me a new appreciation for mach 3.
Anyway, here's the big deal: we think the skip on the lithophane is due to an energy drain somewhere in the process. Perhaps a background process such as a Microsoft Windows update on the puter, (hissssssss, booooooo).
Or, a one line skip could be due to something as simple as starting the blow dryer or starting the vacuum cleaner.
One thing I do appreciate is that it's made in USA and I can get support for it pretty easily.