In message , Bill Wright
writes

The stuff forms a hard bead though which is difficult to get off.

Indeed. I cut quite a lot of the stuff last year, and it takes time,
but my method is Stanley knife first, then pencil in the knife groove
(easier to see), then cut slowly with a hand saw. Fine toothed tenon
saw is good but, as has been said, watch the spine. Finally, a quick up
and down with a surform to remove any bits, and any bead as Bill said.
Easy to form that bead just with a hand saw. My sheet wasn't 10mm
thick, though.
--
Graeme