Geof,
I agree, and the first time I saw it done I was fairly amazed myself. However, provided it's not hard Dural, a few passes with a Stanley knife really will cut it. It's even easier if it's a straight cut not a corner, because after a couple of passes you can bend it off and file the edge. The real danger is sliceing a bit off the end of the fingers holding the steel rule down
David: Ah, the foreigner under the bench, it takes me back
BTW, there are too many Alans in this Forum. I shall have to invent a silly name.
Alan