There have been, I am sure, hundreds of people working successfully
with acrylic who ignore this fact but as you work and carve acrylic
you set up internal stress that is supposed to be relieved by
annealing, not as in metal with a torch but with a kiln. The more
rotary equipment you use the greater the stress so the more work you
can do by hand the better. If you are only using the white or the
black, you might want to switch to Delrin.
If you are using clear acrylic, the greatest stress impact may come
when you use an adhesive to attach the acrylic or when you polish.
The stress can make the joints craze. It can also make the areas
around any drilled holes crack in radiating patterns. For
thermoformed plastics the same thing can happen.
That said, a rotary rasp works well. You can get them at a hardware
store. (Make sure the shanks will work in you flex shaft or use these
in a drill press). Manual rasps also work on flowing organic forms.
For small places, ball and cone burs can do the trick. Most silicone
wheels will leave residue on the piece, as it is hard to use them at a
slow enough speed where they won�t �burn� into the plastic. Take the
finished piece down to 600 silicon carbide for a smooth finish.
Sandblasting as a surface finish works too. For a wonderful tactile
quality, pumice the acrylic. If you need a glossy finish, polish
slowly and carefully (minimal pressure) with a new buff and clean
white diamond or Zam.
The annealing process for acrylic is long and tricky. I haven�t done
it in a long while but I remember a 12-hour cycle with a soak temp of,
I think, 90 degrees. There is a shorter cycle for plastics, which
haven�t been thermoformed (don�t have to worry about the �memory� of
the material). Rohm and Haas or Dupont will have the specific