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View Full Version : Triple-Fluted Drill Bits: Do They Exist?


DougC
01-20-2005, 05:12 PM
- - - 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?
~

danceswithcats
01-20-2005, 05:28 PM
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.

Tuckerfan
01-20-2005, 05:31 PM
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.

Padeye
01-20-2005, 06:48 PM
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.

DougC
01-20-2005, 07:03 PM
....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....
- - - 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?...
~

Valgard
01-20-2005, 07:13 PM
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.

gbrohman
01-20-2005, 07:21 PM
This is the cats Meow.

unibit (http:////amos.shop.com/amos/cc/main/ccn_search/st/unibit/sy/productsx/ccsyn/260/prd/16507887/ccsid/313028103-5082/adtg/01180523)

gbrohman
01-20-2005, 07:27 PM
This is the #@%* for Dollyunibit (http://amos.shop.com/amos/cc/pcd/10690586/prd/16507887/ccsyn/260)

Gary T
01-20-2005, 07:38 PM
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.

Tuckerfan
01-20-2005, 09:14 PM
- - - 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?...
~
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.

Can Handle the Truth
01-20-2005, 09:58 PM
Yes, they exist. You can buy them from McMaster-Carr. Go to

http://www.mcmaster.com

and go to catalog page 2301.

Here's a screen shot of the catalog page:

http://img51.exs.cx/img51/5213/threeflute5jm.jpg

hammerbach
01-21-2005, 02:07 AM
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.

David Simmons
01-21-2005, 02:30 AM
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.

David Simmons
01-21-2005, 02:33 AM
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.

DougC
01-21-2005, 03:31 AM
- - - 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....
~

Desmostylus
01-21-2005, 07:54 AM
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.

GaryM
01-21-2005, 08:06 AM
Another vote for the Unibits! They work great in thin materials. Particularly well for enlarging existing holes.

Mr. Goob
01-21-2005, 10:16 AM
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. :D

Can Handle the Truth
01-21-2005, 02:28 PM
Is there any way you could make a fixture that incorporated Drill Jig Bushings? (http://www.carrlane.com/Catalog/index.cfm/26805071F0B021118070C1C510D020609090C0015480013180B041D1E173C1B08535246)

stanger
01-21-2005, 02:34 PM
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.

Padeye
01-21-2005, 03:46 PM
Mr. Goob, throw a little wisdom on us and tell us what three flute bits are good for.

Berkut
01-21-2005, 04:04 PM
Just how thin are we talking here? .025? Less? Is it Aluminum?

Berkut
01-21-2005, 04:13 PM
Oh, nm, I see where you said the material was aluminum.

Can Handle the Truth
01-21-2005, 04:27 PM
Mr. Goob, throw a little wisdom on us and tell us what three flute bits are good for.

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."

DougC
01-21-2005, 07:04 PM
- - - The 200-odd aluminum holes were in .032-inch sheet and various forms of 1/8"-inch extrusions. This time.
------
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...
~

David Simmons
01-21-2005, 07:52 PM
- - - The 200-odd aluminum holes were in .032-inch sheet and various forms of 1/8"-inch extrusions. This time.
------
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...
~

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?

Can Handle the Truth
01-21-2005, 08:39 PM
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...
~

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. (http://img157.exs.cx/img157/5329/jig8hx.jpg)

Berkut
01-21-2005, 11:16 PM
The 200-odd aluminum holes were in .032-inch sheet and various forms of 1/8"-inch extrusions. This time.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.

Crafter_Man
01-22-2005, 11:42 AM
At work I use knockout hole punches (http://www.irvansmith.com/catalog2/parts/greenlee_hole_punches.shtml) 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.

David Simmons
01-22-2005, 12:34 PM
At work I use knockout hole punches (http://www.irvansmith.com/catalog2/parts/greenlee_hole_punches.shtml) 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.

Blown & Injected
01-22-2005, 01:21 PM
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.

According to Pliny
01-22-2005, 08:45 PM
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.

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