I agree with Zippymbr about using a smaller bit first.
I have drilled about 30 holes in a number of different types of bars (just about all my bars have holes thru the middle of the nose) and have tried just about everything in the way of drill bits. Carbide and carbide tipped bits work (even concrete hammer drill bits) well but I prefer the Cobalt bits because I can resharpen them. I have 3 bits I use for bar drilling, 1/8, 1/4 and 5/16". I start with the 1/8" on about 750-1000 rpm in a drill press with lots of coolant/lube and moderate to high pressure. Then I use the bigger bit on ~250 rpm also with lots of coolant/lube. The pressure needs to be positive to maintain continuous cutting, and don't let the drill chatter in the hole otherwise it further work hardens the steel. Using the bigger bit without the pilot hole works but it's much harder to start and maintain the cutting action and ends up dulling the point after just one or two holes.
I have drilled about 30 holes in a number of different types of bars (just about all my bars have holes thru the middle of the nose) and have tried just about everything in the way of drill bits. Carbide and carbide tipped bits work (even concrete hammer drill bits) well but I prefer the Cobalt bits because I can resharpen them. I have 3 bits I use for bar drilling, 1/8, 1/4 and 5/16". I start with the 1/8" on about 750-1000 rpm in a drill press with lots of coolant/lube and moderate to high pressure. Then I use the bigger bit on ~250 rpm also with lots of coolant/lube. The pressure needs to be positive to maintain continuous cutting, and don't let the drill chatter in the hole otherwise it further work hardens the steel. Using the bigger bit without the pilot hole works but it's much harder to start and maintain the cutting action and ends up dulling the point after just one or two holes.
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