I have down 3 rotary lithos now, 1 of which was a 'successful' carve, and a second which is usable but flawed. Something I just noticed with the last one, which was the first I would consider successful, is that none of them were 'parted off' - I have the diameter of the workpiece set at 3.5", and the part off diameter at 3.313" (106/32 actually). But it didn't even touch the part-off area, there's no marking, and I watched it finish the carving, and it never even tried to part it off. I was expecting a 1/16" or so thick tab left to cut through. Instead I have the full 1/4" pipe wall, and no visual or tactile guide for my hacksaw... here's hoping I can cut it off straight, and have a nice clean edge!
But I would like to know, for the future, why it didn't part it off like it is supposed to? is there a minimum depth before it will do that part-off? If so, what is it?