In article ,
Gunner Asch wrote:

On Sun, 4 Jan 2009 08:38:33 -0800 (PST), Ernst
wrote:

Hello All,

I had the occassion to drill through some very hard fasteners.
Standard HSS bits were becoming dull in a very short timespan, so I
opted for cobalt bits to continue.

Armed with a set of Craftsman bits, I went back to work. Not much
difference. Altering speeds, using light oil, nothing really worked.
Ended up using a Dremel tool with a cut-off disc to remove the
fastener heads (which presents other problems).

What gives?

Regards,

Ernst


Colbalt are tougher, and stay sharper longer, and while a SIGNIFICANT
improvement over high speed steel IN THE PROPER APPLICATION....

they arent miracle workers.

Carbide, on the other hand.....those do work miracles if used properly.
If not, they become nightmares ........

"very hard" indicates to me...carbide.drills are required.

I've had good luck using cheap masonry drills for drilling out hardened
steel fasteners. Flood cooling does seem to help. I've always used a
drill press or mill, but I suppose freehand could work on smaller
fasteners.

Joe Gwinn