On Wed, 11 Oct 2017 15:55:28 +0100, Rob Morley wrote:

On Wed, 11 Oct 2017 05:03:33 -0700 (PDT)
wrote:

Drill bits are prone to crack acrylic. I prefer to use a stone in a
dremel, it mostly melts the hole. No risk of breakage, just take care
to avoid the hole wandering.

Using an ordinary drill in reverse rotation might do the trick, or
maybe grind a bit to have negative tip clearance, so the actual
"cutting" is friction but the flute still clears the waste material.
I'm almost inclined to go do an experiment, but there's so much that
actually /needs/ doing that I shouldn't put off any longer.

It'd need a shallow pit to start without wandering, then a sharp masonary
bit will scrape the material rather than cut it.
At work, we had some backed off bits of about 80 - 85 deg. for material that
would crack with a standard bit.

As an aside, when I wanted a small scraper, I slowly ground a square file
(about 8 - 10mm) with 2 acute angles, 2 obtuse angles and a small chisel
tip. The angles are all sharp and the obtuse ones are ideal for hard
plastics.
It's worth using a good file - not worn out - as then another file isn't
needed for a lot of jobs.
--
Peter.
The gods will stay away
whilst religions hold sway