Triple-Fluted Drill Bits: Do They Exist?

Factual Questions
1
      • So I am drilling various pieces of aluminum for a project I am working on, and I had an old black oxide set of bits, but I wanted this project to look nice–so I went out and bought a brand-new set of titanium-coated drill bits. The problem is that particularly in thin sheet, even these don’t drill round holes. The bit starts to walk around a little and ends up making a less-than-prefectly-circular hole, almost always a “tri-lobed” hole.
        …
  • Well first of all, nuts. The damage can be hidden, but it annoys me regardless.
  • And second of all, it occurs to me that I have had this problem pretty much every time I have used a hand-drill to drill holes in thin metals. It hasn’t really mattered how sharp or dull the bits were. As far as I can imagine, using **triple-**fluted bits would totally prevent this walking around as the drill bit would be resting on three cutting surfaces instead of just two. I know there are milling machine bits that come with various-numbers of flutes, but I can’t ever remember seeing anything other than double-fluted drill bits. Does anybody make them? Why not?
    ~
2

My guess is that a three fluted bit would lose sufficient mass along it’s shaft that it would be prone to breakage, particularly at smaller diameters.

The split-point design is good at staying put, even without centerpunching. Run the bit at a low speed, use appropriate lubrication for the product being drilled, and for larger holes, use incremental sizes and you should be fine.

3

I’m fairly certain that they do (I’ve seen a bunch of specialized drill bits in machinists magazines, but I’ve not paid too much attention to them since they’re so expensive), but in order to solve your problem, I don’t think that you need to go to such drastic measures. You should try drilling a pilot hole with a much smaller (and shorter) drill bit first, and then drill the hole with the final size drill bit that you want to use. You’re less likely to have the drill bit walk on you if you do this.

4

Using a hand drill is part of the problem. Even with a pilot hole a hend held drill will float and often produce out of round holes. You can get a benchtop drill press for under $100.

5
      • Yea, I know–but today I was drilling holes near the center of sheets that measured 2 feet x 2 feet. And some of the stuff I do I specifically can’t or don’t have time to put into a drill press. It’s like a countersink–a countersink has a bunch of cutting edges (way more than two, anyway), and doesn’t chatter around in the hole at all, does it?..
        ~
6

How about one of those $40 “drill press adapters” for a hand drill? You could clamp the plate to your work surface and I think that you’d get a lot less skittering around.

7

This is the cats Meow.

unibit

8

This is the #@%* for Dollyunibit

9

When drilling through thin material, and especially soft material, I find it very helpful to place the work on a piece of wood (say, a 2X4) that can be drilled into.

10

It depends upon the type of material, the nature of the hole, etc. I’ve used multi flute countersinks and single flute countersinks and I’ve found that on harder materials the multiflute countersinks tend to bounce and leave uneven chew marks, while a single flute will leave a clean chamfer.

11

Yes, they exist. You can buy them from McMaster-Carr. Go to

and go to catalog page 2301.

Here’s a screen shot of the catalog page:

12

When I’m drilling thin stuff, I get a bit the size I need and grind the rake to 0 degrees (parallel to the long axis), or make a half round drill. If you look at the unibit, it’s just a stepped version of a half round drill. The problem with the usual fluted drill is that it will tend to walk, and to pull the thin stuff up the flutes. A flat drill, with no flutes, doesn’t do that. You can also just cut off the fluted section, grind on a conical tip, and grind away half the thickness of the tip. This very simple drill does a nice job for me in soft sheet metal.

13

Unless you have special sheet metal drills, one way to get round holes is to take the time to sneak of on them. Start with a small pilot hole. The in a couple of more steps get a hole that is 1/32’ or so under size and finally ream to final dimension with the right size drill. It isn’t perfect and wouldn’t do for volume production, but for home projects it works just fine.

14

If you are really fussy you should clamp the work in place and not move it during the drilling. Leave the work in place and just switch drill bits. This can be a bit of a problem unless you have a drill press with a fairly long throw.

Of course if you are using a hand held drill this won’t work and you have to work up to the final size in small steps.

15
      • Yikes! The MacMaster-Carr ones are carbide, and priced rather luxuriously. …I guess if I really needed one particular size it might be worth the price to order one bit, but I don’t think I’ll be buying a whole set anytime soon… If you should happen to run across any regular-tool-steel ones, perhaps ti coated, speak up about it…
        ~
16

The number of flutes on the drill ain’t the problem. The problem is wobble. You’ve already been given the right answer by Gary T, padeye and David Simmons.

17

Another vote for the Unibits! They work great in thin materials. Particularly well for enlarging existing holes.

18

Yes there are three flute drills. You will pay dearly for them. Not recommended for aluminum anyways. Being light and gummy aluminum makes long stringy chips that need better evacuation. It would wad up quickly in a three flute drill.

Oil, a good centerdrill, firmly clamped workpiece, and a wood board for a backer have all been mentioned and I wholehartedly agree. A drill press is the best option, but not always feasable like you said.

I’m not a big fan of doing multiple holes as long as you have a good spot predrilled. Please use a centerdrill not just a pin punch. The problem is the center of the drill has no support and and will wander all over the place. Also it unnecessarily beats the hell out of the cutting edges of each drill shorting their lifespan.

TiN coating mostly overrated for the home market. A waste of money. Unless there is a lot of heat generated or you are drilling unusual material the results in a hand power drill will never be noticed. Bright HSS is fine for 99% of home use.

Too bad it’s against board policy I’d give you my company phone number for a sale. :smiley:

19

Is there any way you could make a fixture that incorporated Drill Jig Bushings?

20

There is a type of drill bit called a Parabolic bit that I believe is designed to drill a more accurate round hole.

Also available are bits that are a drill point on the end and taper into a reamer. This allows you do drill the hole close to size and then finish round and accurate with the reamer part.