wrote in message
oups.com...
Every time I want to open up a hole, I reach for
my Air Grinder or
Dremil and use a 'stone' grinding bit. But it
never seems to do much
and wears out quickly.

I was recently at a Motorbike exhibition and
there was a tool stand,
which had a range of 'bits' which were
completely metal! They came in
all shapes and sizes (balls, cones, cylinders
etc) and had various
patterns sliced into them. Some had horizontal
and vertical slots cut
in them, leaving a load of sharp edges, and some
had a 'cork-screw'
like pattern cut around the outside.

Since then I have been looking for 'bits' like
this and can't find them
anywhere. None of my tool catalogues show
anything remotely similar.
Does anyone know what these tools are called?

Are they designed for 'grinding' in general, or
did I misunderstand
their use?

Any info would be appreciated

Jon

I think what you saw were tungsten carbide burrs.
They do take a good size bite. Even the fine ones
leave a rough surface, so it's a good idea to
finish with a stone of the surface finish is
important.