As I reported earlier, I had achieved great success in cutting PCBs at a 0.05mm depth, without auto-leveling, but instead only by pre-leveling my sacrifice board. I use MDF, and it seems to warp (at least more than 0.05mm, across a 4"x6" board) over time. Pre-leveling resulted in most, but not all, of my PCB’s cutting very nicely. But, the occasional exception frustrated me. In search of an answer, suspecting that some of my cheap Chinese boards are not as flat as they look, and inspired by some other recent posts, I purchased a vacuum table (about $130, plus $60 for a pump, on Amazon). Three PCB boards later, I believe I have achieved pretty near perfection.
I recall an only post in which the poster seemed to say he used MFD as a vacuum board – he pumped air out of it and it ostensibly held the circuit board firmly in place. That did not work for me, although MFD does pass alot more air than I would have guessed. I ended up drilling a bunch of holes in my MFD sacrifice board, to correspond to the holes in the vacuum table, and that (with painters tape around the perimeter of the PCB) pulls enough of a vacuum to hold the board very flat.
And I think this explains why autolevel didn’t work very well for me. The autolevel probe never actually exerts any downward pressure on a PCB, since it stops as soon as there is electrical contact. So, it produces a faithful map of the pcb surface, but does not account for the partial willingness of the PCB to flatten under the pressure of actual cutting. (And it seems that relatively great force is necessary to penetrate the PCB copper layer, but once penetrated, it pops right back up.)
Anyway, hope this helps others.