"Ernst" wrote in message
...
snip--
1. I'm basing comparative performance on experience in a
manufacturing environment. Once had to remove a fastener made of very
hard material (set screw as I recall). Went through several HSS bits
and barely made a divet. One of the other techs provided me with a
cobalt bit that went through the piece like butter.

By hand? I'd be surprised if that was the case. What cobalt offers is
hardness at elevated temperatures. In the case of the set screw, money
says that you heated the screw to the point of hardness collapse. It
doesn't take much if it is hardened by the carbon cycle.

2. I am using a hand held drill motor, variable speed, and have tried
several rates from slow to max.

You've already been wished good fortune. I'm going to suggest that it
probably won't happen. Cobalt drills have a much heavier web than plain HSS
drills, so the pressure required to drill is much greater. I doubt you can
keep the needed pressure on the hardened piece long enough to raise the
temperature to the point where it will drill well. Any chance you can
tip the building on its side and get it under a spindle with a lever feed?
g

Harold

3. These fasteners are used to hold storm shutters onto window
frames, have been in place for a while, and are apparently made of
nuclear-grade steel. I can't imagine why such a hard fastener was
used in the 1st place; I've had less trouble removing a broken head
bolt from a 302 with the engine in the car......

Lopping off the heads with a Dremel leaves the remainder of the screw
in place (obviously) which pins the screen frame to the window frame.
Trades one problem for another.

I have nine shutters to go.

Ernst