Linda, Depending on the scale of the grinding you wish to do, I have
found that metal burs and grinders (the kind that are sold for Dremel
tools) do the job the best for small amounts of grinding. Sanding
type surface get clogged very quickly and are somewhat ineffective.
The metal burs (which are somewhat coarse) are available in a variety
of tip sizes and shapes. Suggested bur #'s are 131 (these are the
Dremel pack #"s) which is an ovoid shape, 192, a ball shape, and 196
a cylinder shape. You can buy sets of the burs (Foredom sell them)
which gives you a selection.
The speed at which you grind is important – too fast and the acrylic
gets gummy – you can smell when this happens (the fumes are toxic)
and you should slow down. The temptation is to do the job quickly,
but actually a slower speed is more effective in the long run.
Make sure you wear goggles and a dust mask when working in acrylic -
I had a very nasty encounter with a piece of acrylic in my eye when I
first began (and this was when I was wearing goggles too – the
acrylic entered my eye afterwards)…