On Oct 10, 12:05*pm, Dave Osborne wrote:
Will wrote:
Anyone know why you can't buy diamond drills - I have a diamond saw but the
hardest drill I have is HSS Cobolt?

Because diamonds "grind" rather than "chisel".

For drilling stone, there would be no advantage to making a diamond
drill over a TCT drill and it would be a lot more expensive.

For drilling wood or steel, the grinding action of a diamond drill would
* be inefficient compared with a tool that cuts ("chisels"). Now, if you
could make a solid diamond tip for a drill and put a cutting edge on it,
that would be awesome (assuming it wasn't too brittle to be of any use).

It would be too brittle. The way to make practical hard material bits
is to embed little pieces of the stuff in a softer matrix. That gives
he hard cutting material plus the slight flex of the softer stuff,
thus eliminating the brittleness.

Diamond drills do exist, but for wood they're just not necessary. A
properly designed bit will do a fine job - unfortunately many are
still struggling along with ill suited bits like twist drills.


NT