Depends entirely on what tolerance you are marking/cutting/bending to. I
want my students to be able to cut/bend to ten thousandths accurately and
the only way to do that is to scribe. THen again, we are only building
electronic chassis out of aruminum (5052H32) and we don't worry much about
it cracking under vibration.

When I build small airplane parts and have to hold that sort of tolerance,
I'll lay on a thin coat of machinist's bluing and scribe very carefully so
that I only cut the paint and not the aluminum itself.

Doing it on a wholesale level, I might be tempted to lay down a spray paint
of some sort in a dark color and scribe the paint, then wash the paint off
with solvent.

I've never used one, but I've seen professional tinbenders use a special
metal-marking pencil that does NOT corrode or otherwise weaken the surface
of the metal.

Jim


"Michael Horowitz" wrote in message
...
I want to mark sheetmetal for bending.
Can't use a scribe because I'll weaken the metal.
Magic Marker is too thick.
Pencil doesn't show.
What do you use? - Mike