Mr. Goob, throw a little wisdom on us and tell us what three flute bits are good for.
Just how thin are we talking here? .025? Less? Is it Aluminum?
Oh, nm, I see where you said the material was aluminum.
Until Mr. Goob comes back, here’s a quote from the McMaster catalog page: “The self-centering three-flute design creates more accurate holes and superior finishes at higher production rates than standard carbide drill bits. An excellent choice for drilling in alloy steels, cast iron, high-silicon aluminum, and nonferrous materials.”
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- The 200-odd aluminum holes were in .032-inch sheet and various forms of 1/8"-inch extrusions. This time.
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Also, I think the vast majority here are still not understanding my objection: I don’t want to have to drill two holes, dammit!!! I want one drill bit of a given size that when used in a hand-held drill, can reliably make a round hole, on one pass, and that isn’t limited to thin materials…
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I’d like to be 21 years old.
Just how much are you willing to spend for this miracle? And exactly how “round” do these holes have to be?
Sorry, buddy! What you’re looking for doesn’t exist. The only way you are going to get good round holes with a hand-held drill is if you guide it with a drill jig bushing. They’re not that expensive – about the same cost as a TiCN-coated drill of the same size. You could make the jig plate out of wood. Look at this setup.
Huh. I’ve drilled billions (okay, maybe not billions, but a whole bunch) of holes in .032 and .025 aluminum sheet while building and repairing aircraft structures. I don’t have many problems with the holes. I use an automatic centerpunch, an air drill, and a sharp #40, #30, or #21 bit, using some wood as a backing. For larger holes I use a Unibit, if possible.
At work I use knockout hole punches to make holes in thin metal. We have them in sizes ranging from 0.25" to 4" in diameter. Pricy, to be sure. But it’s the Cadillac way to make holes in thin metal.
Yeah but gee whiz. You have to drill a pilot hole, then assemble the hole punch, use a wrench to operate the punch, take the punch apart to remove the scrap, drill another hole, assemble the punch etc., etc., etc. And they won’t work in a hand drill either.
It can be done. Use way less pressure and let the bit cut its way into the metal. I have even seen 5/8" holes in 1/4" steel that was not round because way to much pressure was being used. Once the tip of the bit gets thru, the flutes try to screw the bit into the metal - this also pulls the metal towards the drill.
It sounds like the bit is not cutting all the way to outside edge. For aluminum, use higher speed and less pressure.
Not that this is an issue in this case but IMO keeping the bit cool with a flow of cutting fluid will do way more than any coating.
I have some 4-fluted drill bits, but they are different in other ways as well. They are spun the opposite direction, and are very steeply inclined (go from tip to shank of the bit in one turn). That’s because they are designed for only one purpose, to unscrew those special screws they use installing public toilet privacy walls. You know the screws with head slots that are sloped to make the screwdriver slip if you try to loosen them.