On 22/05/2019 22:11, Bob La Londe wrote:
On 5/22/2019 9:49 AM, Leon Fisk wrote:

Do you have enough material to just drill a bigger hole, thread and use
a larger set screw?

I don't know how hard the tool holder is, but that's not a bad option.

I recently used some diamond hole saws to remove the remains of a broken
HSS tap in a harder steel. Cheap Chinese hole saws but each went in
about 1/4" before losing it cutting ability. I went through 3 and then
just pulled out the remnants of the tap, haven't tried to finish the
tapping yet, may temper the part slightly before trying to finish the
tapping. The part is an ER16 collet holder which I was tapping 3/8" UNF
to suit a Broom Wade die grinder as I have ER16 collets and thought it
an improvement on my previous homemade collet and collet holder..