wrote:

On Sunday, 3 May 2020 00:42:58 UTC+1, Roger Hayter wrote:
snip


Another error is using them too near the edge of a thin sheet. DAMHIKT.

That is precisely the problem. Hand operated qmax Punches use a non-flat
cutting edge to keep peak forces within practical limits for human, screw
thread & spanners. So the metal is at once trying to conform to both
flatness and the bent steel created by the punching action. The lack of a
large enough thick enough sheet causes distortion, sometimes severe enough
to produce only scrap. That's what happened.

And in the current situation, once again holes are required near an
unsupported edge. Don't really want to write off the CU, so the punch
option seems risky.


NT
If there's room, how about clamping the edge in a vice? I've never
tried it, though.

--

Roger Hayter