Andy Dingley wrote:
On 20 Dec, 19:09, Tim W wrote:
Dave

Has anyone come across them before?

Cobalt-unobtainium alloy drill bits have been around for decades, but
are a very niche market. Locksmithing is one user of them, for
drilling hardplate in safes. Certainly the chap demonstrating drilling
through files was at the model engineer exhibition 30 years ago.

They're less useful than you'd think. Just how often do you need to
drill something that won't respond to a carbide masonry bit, or decent
HSS ? I've used mine a few times (every couple of years), but always
for demolishing stuff, not for fabrication. As always when drilling
out broken drill stubs etc., wandering sideways into the softer metal
is a huge problem.

One way round that, is to obtain some high carbon steel bushes with the
right size hole in the middle and a bush holder to clamp to the job,
even it it means drilling another hole to attach it. The closer the
drill bit is to the clamp, the better. It helps to prevent any circular
rotation of the bush holder.

Dave