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Old 12-30-2006, 12:18 PM
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Default Drilling mild steel

Well this seems like a logical place to ask this. What RPMs do you use to drill mild steel? Lets say less than 1/2inch steel and no bigger than 1/2 bits?
I don't need to very often so I just use HF bits and my dewalt drill. They seem good for about a dozen holes, lol

Thanks, Dan
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Old 12-30-2006, 01:15 PM
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hope this is small enough....hope it prints better than it looks ....well it is after 12 ....so i will be off to the pub
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Old 12-30-2006, 01:58 PM
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spend the money for a set of the black cobalt bits and then use them forever.
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Old 12-30-2006, 04:15 PM
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Quote:
What RPMs do you use to drill mild steel?
25 SFM (hand drilll or drill press with no coolant) is a good speed for long drill life. That means a 1" drill at 100 RPM, 1/2" at 200 RPM, 1/4" at 400 RPM, etc.

One simple formula is:
Spindle Speed = SFM /.262 / Stock Diameter
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Old 12-30-2006, 04:25 PM
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Awesome, thanks, now to over complicate it.
I am surprised to notice that the smaller the bit , the faster you go.
Why is this?
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Old 12-30-2006, 04:31 PM
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Best way I can describe it is a vehicle speed limit, the smaller the tire the faster the tire must turn to achieve it. Big tire slow rpm, small tire, high rpm.

Each size tire requires a different rpm to achieve the same surface feet per minute.
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Old 12-30-2006, 04:48 PM
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Thanks irn, that dang near makes sense to me. Not always an easy thing to do
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Old 12-30-2006, 06:57 PM
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Quote:
Originally Posted by precisionworks
25 SFM (hand drilll or drill press with no coolant) is a good speed for long drill life. That means a 1" drill at 100 RPM, 1/2" at 200 RPM, 1/4" at 400 RPM, etc.

One simple formula is:
Spindle Speed = SFM /.262 / Stock Diameter
Dang Barry, that is very concervative. I usually run 100 SFPM (surface feet per minute) dry and have good results.
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Old 12-30-2006, 07:28 PM
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My understanding is that a larger bit generates more friction due to size therefore must spin slower.
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Old 12-30-2006, 07:33 PM
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its kinda like the transmission in your vehicle bigger load means more power and a slower gear to move it. same with bigger bits, large bits create more load or drag thus a lower gear or speed works better as some drills have a small motor.
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