Too much speed work hardens the steel and quickly dulls the bit. Sometimes I’ll use a carbide drill to break thru the work hardened surface then go back to HS drills. HS drills are not all the same. USA made are far superior to imports. Titanium coated from HF are the worst.


Phil
Moderator, The Engine Shop, Interiors and Project Journals

1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube
Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes
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