tnik wrote:

I second that, great info Ed. Thanks.

I did know that Cobalt tooling was actually HSS with cobalt mixed in..
Only reason I was animate about getting cobalt or carbide is because I'm
trying to drill out some nasty hard bolts, and I know damn well HSS
would snap off in a heartbeat. Just trying to make a simple job a bit
quicker.

Maybe you ought to reconsider left hand and carbide.

A while back I had to remove a dowel pin that was broken off flush in a detail that it was
impractical to try to drill an intersecting hole to do the grease and dowel pin trick
(hammer also needed).

So I carefully located the part and used a smaller 2 flute carbide endmill that was going
to cut a hole tangental to the existing dowel pin. So far so good.

Well when I hit bottom, the dowel pin lost tension, the endmill still had a bite and I
watched the Bridgeport table move x and y in about a .25" range until I could hit the stop
switch which came at the same time the R8 collet unscrewed itself from the draw bar.

So when you get a good bite on your bolt and the bolt starts backing up, what is going to
happen to your brittle carbide drill? Likely it is going to snap.

Consider RH tooling, use carbide drill or center cutting end mill sized on minor diameter
of fastener. Pick the remaining threads out.

Wes