On Nov 18, 8:53 pm, Tony Hwang wrote:
Hi,
What is toughest drill bit for drilling many, many holes
thru a bolt stuck in a confined space. I am trying to drill
it into bits to break it off. There is no other means to get rid of it.
Cobalt bit or any other better one?
TIA,

When I've taken things to a machine shop to get
a broken hardened bolt removed, the guys have
used a carbide bit in a drill press using light steady
pressure and sometimes a lubricant. I have used
a Dremel tool with a carbide tip to remove broken
grade 8 studs when making equipment repairs.
You can carve it out and sometimes use a small
chisel to break out the fragments.

[8~{} Uncle Monster