The mysteries of the drill bit

Well, you must be doing something wrong. What tools do you have? A hand-held electric drill? A drill press? A millinbg machine? You won't get really good holes with hand-held. The right RPM for a specific drill size and workpiece material helps a lot. What aluminum alloy? Some drill very nicely, some are gummy and a big hassle. Are you using coolant? Even a drop of "thread cutting oil" from the hardware store will be a big help. The right feedrate for advancing the drill also helps.

I have drilled literally tens of thousands of holes in aluminum, mostly using a Bridgeport mill (since the mill can serve essentially as a drill press, I don't have a drill press.) I almost always use either coolant or cutting oil. I have used the same set of Indian-made drill bits I got from Harbor Freight 20 years ago. I occasionally resharpen them freehand on a bench grinder.

What you are doing is NOT considered hard at all. If you want a REALLY clean and round hole, use a reamer. Then use a countersink or deburring tool to clean up any ridge at the surface.


Reply to
Jon Elson
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Maybe somebody smarter than me can figure out what is happening here... I do a lot of drilling in aluminum. Anywhere between 1/16" and

1/4" thickness and between 1/4"-1/2" in size usually. I have no idea why, but the only drill bit I have been able to cut very clean holes with, is a basic HSS black oxide bit from Hitachi. There's nothing special about them, but they work very well. I've tried what seems like every other type and brand of bit known to man, and none will work as good as the Hitachi... I've even tried centering bits and other much more expensive ones. When I look at the Hitachi, I don't see anything different about it as compared to numerous other bits. It's got the same angle and everything as at least 10 others I've tried, but they don't work. Usually I just get a sloppy hole with ridge build up, messy sides, and less than perfect circle.

So why not just buy the Hitachi ones then? They just started offering a new kind and you can't get the old ones. The new ones don't work either.

It's a stupid problem, but I can't figure out what the deal is.

Thanks for any help,


Reply to

It sounds to me like the surface treatment on those bits kept the aluminum from gumming onto the bit. I bet you could use any old bit as long as you use the right speed and use some kerosene for lubricant.


Reply to
Grant Erwin

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