Re: Carbide counterbore

Gary Mason <carncrows2004@...>

Hi Neal,
If the gear is "case hardened"? and it sounds like it is, as you've managed to drill through the case hardening and into the gear with a carbide drill bit. Could you c/b for the screw head diameter plus clearance using another carbide drill, then put a shoulder at the base of the c/b using a hss drill bit ground flat with appropriate back rake to square off at the base.The steel should be reletively easy to drill below the c/h with slow rpm and good cutting oil.

nwinblad@... wrote:
Does anyone know where I can buy a carbide step drill or counterbore for 4-40 pan head screws. I need to put some screws into a hardened steel gear. I can't seem to find a carbide step drill anywhere. I tried drilling through this stuff with a cobalt drill and it wouldn't touch it. Then I chucked up a carbide drill and it goes through it nicely. Now I just need to find a supplier...

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