coloured burs

[Don Dougan <dondougan@xxxxxxxx>]

Andrei;

"a Dremel-like set of burs. They come in three colours: white, pink,
and grey. What do they mean?   And what specific use do the various
shapes have - conical, spherical, cut-off cones, etc.?"

The white, pink, and grey (and brown too) stones are all different grades
of aluminum oxide abrasive.  They work great for metal, but for stone
you want silicon carbide (SiC)which are colored green or black.  As far
as the shapes go they are pretty much as described: the conical is a cone
with the shank coming out the bottom (like a traditional "Christmas
tree"), the spherical is also known as a 'ball' shape, and the cut-off
cone is a reverse of the conical - the shank comes out of the small end
of the cone.

For softer stones (soft limestone, alabaster, soapstone)  the aluminum
oxide burs will work OK, by they tend to start 'glazing' as the abrasive
particles dull on the harder types of stone (marble).  You end up more or
less burnishing the surface instead of abrading it.  They will not do
much of anything on materials as hard as granite -- the abrasive only
slightly harder.

Silicon carbide (SiC) gets dull by fracturing-off and leaving a sharp
edge as the stone wears down.  The silicon carbide stones are usually
bonded together with a softer matrix than the aluminum oxide, thus the
sharp-edged particles of silicon carbide are constantly being exposed.
This means the SiC stones wear down rapidly, but they cut cleanly right
up to the very end.

Save your money for diamond burs -- they  are delicate, but with care
they will outlast  silicon carbide many times over.

Good grinding,

Don Dougan