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Old 08-22-2013, 12:20 PM   #1
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Best drill bit for steel?

I need to drill a1/4" hole in an 8" I beam, it's a remote job and I don't want to be running into town to buy bits, can someone tell me what the BEST drill bit would be for this application?



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Old 08-22-2013, 02:09 PM   #2
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I have successfully used titanium nitride bits to do a similar job. You need a high torque drill, and plenty of lubricant. Low speed is better than high speed based on my experience, but you can actually get charts that show required speed for steel based on bit size. You can do this job using cobalt bits, or even black oxide bits. With the black oxide, you only get a few holes per bit. Make sure you get metal drilling bits.


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Old 08-22-2013, 03:17 PM   #3
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Best drill bit for steel?

I just visited with the knowledgeable counter man at the machine shop I do business with and ask if a person walked in off the street to buy a bit and wanted to drill mild steel he would recommend high speed steel bits. If steel in the range of grade 8 was to be drilled he would recommend cobalt.

Your 1/4" bit rpm calculates to 1,440 with a cutting speed of 90 feet / minute for mild steel. A little slower would be ok. Harder / tougher material will have less than 90 fpm cutting speed and will calculate to less rpm. Formula: cs x 4 divided by the diameter.

Use a cutting oil not lube oil, available in aresol and an occasional squirt is all that's needed. Water would be better than any lubricating liquid.

Last edited by SeniorSitizen; 08-22-2013 at 03:20 PM.
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