A simple way to Tri-cut the butt of a drill bit?

You want 3 flats on the shanks of drills so they don't slip/spin in a chuck when in use?

I've done it freehand with a stone in a Dremel/rotary tool for some purposes where accuracy wasn't critical. A file works well for knocking off a burr from the shank that's been formed by slipping.

To use an indexing method to achieve the 120 degree spacing, something hex shaped which can be secured to the drill can be used, turning the hex two facets for each flat. A drill chuck with chuck key holes can be used for somewhat accurate 120 degree indexing, using a pin or stop moved to each of the 3 chuck key holes in the chuck body. The issue then becomes utilizing a stop for the depth of the flats so they turnout uniform.

A good practice is to tighten a chuck with a chuck key at all 3 positions to get the best holding power of the chuck.

Why?

And what kind of drill bits?

I can't remember where I discovered this (probably in this group), but it is invaluable when running larger bits. You'd think it would be something the manuals would want to include.

Jon

I don't recall if the shop class teachers of the '60s taught this, but I do remember a tool salesman telling me this about 1980. I thought he may have been making excuses for his tools, but it does reduce drill slippage to almost nonexistent (even moreso now with lower quality chucks being abundant).

As a cheap index, you could drill through a hex nut and then slide the nut onto the shank of the drill and epoxy it there. Once dried, use it as an index and grind the flats using something like a table saw with an abrasive wheel mounted in it. Pop off the nut when you're done. You can weigh the drawbacks and dangers for yourself.

get a collet block and 1/2 5C collet

then clamp in vice, file, rotate, repeat

karl

Pick up a collet block set (there are two forms -- square and hex), and some 5C collets to fit the drill bits (just a 1/2" one apparently). Clamp the bit in the collet with the shank sticking out, put the collet block in a vise, and set up a pair of rollers made from ball bearings on either side. The bearings will limit how far down a file will cut. When one flat is cut as deep as the bearings will allow, loosen the vise, rotate the block two flats and clamp it again in the vise. This is a way to do it with no power tools, at least. This should get all three flats the same depth, so the drill won't run off center.

If your "grinding" includes a surface grinder (not likely with the "basically no machinery" restriction, just the collet block, the collet, and the mag chuck in the grinder should be all that is needed.

Good Luck, DoN.

Cool. :) Thanks DoN, Denis G. and Karl Townsend! And everyone else that responded, trying to help. :)

Collet block or even a nut with a home drilled and tapped set screw is the sort of technology I was looking for. Just needed some sort of way to index it. Length and depth will be worked out later and will definately look into the bearings as "file stops". :)

I believe the largest drill bit I have is 1" steped up in 1/16" and some "fill-ins" that are 1/32" steps.

The Enco URL was especially useful with it's picture and all! :)

For the "other guys"...

As a kid I fiNgured out that tightening the drill check using all the holes and going round and round from one hole to the next until no more progress could be felt helped a lot. A kid kinda-has to with weak "kid" hands. ;)

But even now, sometimes the chuck needs a little more than that. ;) Some of the larger drill bits I've got have the three facets and work great! :)

The German all steel keyless chuck I'm using grips the drill bits pretty dangged good but the faceted bits, it grips better. ;)

Thanks a lot guys!

Anybody got anything to add, fire away. :)

Alvin in AZ ps- Been a long time since I was on a newsgroup, it's cool to see familiar names like yours DoN. :) Karl Townsend too? :)

For indexing, get a spare chuck that takes a key you already have. A chuck with a 3/8-24 mounting thread is useful to hold and grind small parts if you mount it on a long bolt.

Chuck the drill bit in it backwards, insert both keys and clamp the chuck in your bench vise with both keys resting on the vise jaws. Grind the flat parallel to the tops of the jaws, the bench leg under the vise, or some other convenient visual reference line. Repeat with the keys in the other holes.

I tried this as far as running a file across the bit, parallel to the jaw tops, but I'm not going to risk damage to a bit or file actually cutting the three flats.

If you have a belt sander one key should be enough to keep the chuck from rotating as you hold it on the table to sand in the flats. This light and compact style of sander substitutes for both a bench grinder and a larger belt sander for most of my home shop jobs:

The platen behind the lower part of the belt lets you grind flat and square, the unsupported area above is good for rounding off sharp ends and edges. The version with a disk on the side may be better for woodworkers but I prefer a larger horizontal belt sander (or a plane) for smoothing sawn edges.

jsw

IME, the shanks of HSS drills are typically soft enough to file without damaging the file. If the shanks weren't softer, they would be much more difficult to chuck without slipping, and likely be a lot more instances of broken drills.

The results would be like chucking an endmill, which will work in some instances, but is generally a bad practice since most drill chuck jaws aren't treated with diamond dust for adequate gripping power of hard HSS.

x2! :)

-All- the ideas have been helpful. :)

And Wild_Bill's got it right about drill-butts being soft up to a certain spot too. :) (that spot varies;)

I got this but it's not square like yours is, JW...

I "could" make something square tho, I think. xD

But I've been wanting a chopsaw for a long time... ;)

Alvin in AZ

Was taught this in the late 70's Vo Tech. However, the emphases was on three jaw *lath* chucks, not drill chucks. Personal safety being more important than preserving drill bit shanks.

O.K. So you need the full set of collets -- if using a collet block.

Been there. :-) Maybe as I get older, I'll be there again. :-(

A Rohm (or is it "Rolhm"?) clone of an Albrecht chuck. Yes, those are good -- and self tightening -- unless you are trying to use a left-hand drill bit. :-)

Welcome back! (And keep your killfile well tuned to get the noise-to-signal ratio somewhat better. :-)

Good Luck, DoN.

Up to a point. Then you get to the import ones which are soft all the way to the tip, and turn into reverse spirals the first time you seriously attempt to use them. :-)

With the exception of certain models of Albrecht drill chucks, which do have the diamond grit for that very purpose. (There may be others, but the Albrecht are the only ones I know of.)

Enjoy, DoN.

With a tradeoff here. If you tighten on all three holes (for chucks which *have* three holes -- some only have the single master key hole), while you get a tighter grip, you are likely to get more runout than if you tighten in the master key socket (usually marked with something like a '0' stamped near it.)

Enjoy, DoN.

I wouldn't grind on the side of a chopsaw wheel. I had a misused cutoff disk fly apart on my surface grinder, which is too heavy to jump from the imbalance, but the fragments became shrapnel.

Perhaps you could mount the sander on a plank that supports a wooden work table. jsw

Yeah, it prob'ly wouldn't be stiff enough to work right anyway. :) Mostly not thinking, just picturing how square they "look". ;)

Yeah, it's not as fun as a carnival ride but just as exiting. LOL :)

What all did the pieces stick into and how deep did they go? :)

Little handgrinder cuttoff discs 4", 4+1/2", 5" fly apart all the time but they're light weight and don't penetrate, just kinda hurt and spook the heck outta ya! LOL :)

Alvin in AZ

All of 'em have a 1/2" butt tho. xD

I don't have a 5/8" or bigger chuck. :/

Never found one at Kent's Tools in Tucson that had threads.

Kent needs to figure out a way to franchise his business. His used tool store is the coolest store ever! :)

Yeah, that's the brand, wanted to post it but wasn't sure enough of the name. ;)

Cool, thanks for the welcome back, DoN. :)

But. ;)

"kill files are for sissies! :)" -Alvin in the 90's

YMMV? LOL :)

Butthead in AZ