Yep, Rons got it.
The fancier cutters have a strip of wood or more recently plastic where the blade ends up, so it doesn't actually touch the machine table.
The strips wear as they're supposed to, and the blades get dull as well. Once you've got a dull blade cutting into a worn wear strip the cut gets ragged as there's a bit more tearing than cutting happening.
One of the cards I have was rejected from grading as "miscut". Within the allowable size, not trimmed, but a very ragged cut top and bottom.
Steve B
I made a few parts for a prototype papercutter that had a wear strip that could be moved up a few thousandths of an inch so the blade would be cutting into a fresh part of the strip. .003 wall stainless tubing with hydraulic fittings brazed on. it worked ok, but was fragile and the brazing wasn't at all easy.
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