Making stubby drill bits

[Rotate]

I had to drill a 1/2" hole on a part that tall enough that my standard 1/2" drill bit was too long. Over the years I collected motly collection of bits, and I decide to sacrifice one of the bits by shortening the shank. To get the clearance, I had to grind off almost the entire length of the shank. To my horror, the drill chuck couldn't grab the fluted portion of the drill. After looking at the flute and the drill chuck, it became obvious why. The drill chuck has three jaws and the drill only has 2 landing area. Lesson learned.

Now how do you properly shorten a drill bit?

Albert

[mikem]

Maybe you could slip a sleeve with a slit in the side over the shortened bit to grip the bit in the chuck. The wall thickness would have to be stiff enough to not deflect too much when the jaws clamp down on it where the bit doesn't have metal there to be gripped by the jaws of the chuck. Thanks--Mike

[Uncle Dunc]

Shorten the point instead. The flute length only needs to be a little longer than the hole you're trying to drill. Buying a Drill Doctor or learning how to sharpen a drill freehand may seem like a steep invertment for one hole, but once you do it, you'll probably wonder why you ever put up the the flex, the inadequate tool space, etc. rather than just getting a shorter drill.

[metal mite]

Rotate
Cut the other end off and resharpen it, or get a screw machine drill.

Screw machine drills are short drills that hardly need a center drill they are so rigid.

They are used on screw machines and turret lathes because of the short stroke of the turret, and can eliminate spot drilling operations.

Or put it in a collet instead of a chuck if you're in a mill.

mite

[Stepside]

The Mite is Right. Get a screw machine bit. In fact save your coins and buy a whole set---98% of the time you will wonder why they even bother to make the jobber length bits. I find for most work they eliminate the need for a starter bit. Now for .250 and larger holes in sheet goods get a set of annular cutters if you want round holes.

[halfnut]

Mite is right, cut down working end, shank is soft to allow the chuck to bite. Could buy one of those new Albreight chucks with the diamond coated jaws. But that won't work if you are past nice round part.

Just cut off the cutting end, regrind it. Remember that the web will be thicker now, it will have to be thinned or split. Easy if you have a drill grinder that does this, not hard to do with a grinder freehand if you have a sharp cornered wheel.

[This message has been edited by halfnut (edited 05-19-2002).]

[Peter Sanders]

Hi Albert

<font face="Verdana, Arial" size="2">Originally posted by Rotate:
I had to drill a 1/2" hole on a part that tall enough that my standard 1/2" drill bit was too long. Over the years I collected motly collection of bits, and I decide to sacrifice one of the bits by shortening the shank. To get the clearance, I had to grind off almost the entire length of the shank. To my horror, the drill chuck couldn't grab the fluted portion of the drill. After looking at the flute and the drill chuck, it became obvious why. The drill chuck has three jaws and the drill only has 2 landing area. Lesson learned.

Now how do you properly shorten a drill bit?

Albert
</font>

I don't propose this as the "proper" way to shorten a drill bit, however I am sure that if you were willing to sacrifice a drill bit you could use an angle grinder to cut off most of the drill bit (without overheating of course) and then sharpen the remainder. As it was pointed out though, don't forget, the web will be thicker and you may need to relieve some of this to retain a good cutting edge.



------------------
Kind regards

Peter

[Thrud]

Albert

Mite is right, spotting drills or stubbys. If you have a collet holder non-taper length drills can be gripped by the collet but you won't gain much unless you have a NT40 or NT50 shank tool holder (more empty space behind the collet).

[lynnl]

Question: (..regarding Halfnut's comment about thinning the web). Why is that necessary? I'm not taking issue with it. I've seen that mentioned before, but I've never really understood the purpose it serves.

[metal mite]

Lynnl,

Most of the feed pressure in drilling is created in the web.
The lips cut freely because of the positive rake.
The web is for all practical purposes, wearing the metal off.

The web area will work harden stainless steels while drilling.
Split points, or a special " S " grinds are frequently used on stainless.

You run a lead drill thru so you don't have to force a large drill's web thru the metal.

mite

[halfnut]

Mite is right, it rhymes, had to repeat that once again.

The web of a drill bit gets thicker towards the shank, as a drill is shortened by cutting off or repeated sharpenings this needs to be thinned or the web split.

I was perusing through a catalog the other day and noticed some drill bits that were advertized as having an equal thickness web the lenth of the flutes. This is an exception and not the norm.

[lynnl]

But it would seem to me that by the time the web'ed portion gets down into the hole, the lips have already converted that metal that used to live in that hole (ahead of the web) into chips.

Tho I can see that as the web gets progressively thicker, back near where the fluting ends, the clearance space for chip ejection will be diminished. ... Okay, I guess I can kinda understand it.
Thanks for the additional explanation.

[Rotate]

I checked out the screw machine bits and they sure are expensive. For the price of a 1/2" bit, I can buy a whole set of the regular bits. As usual, I have follow up questions.

a) Why are they so expensive?
b) What are they used for?
c) Why are they called "screw machine bits"?

Thanks.

Albert

P.S. I asked these questions to KBC salesman, and I got the usual "I only sell this stuff" line.

[Uncle Dunc]

&gt;&gt; Why are they so expensive?

One drill is always going to be more than the per piece price on a set, but probably what happened to you is that the one you bought is a better grade of drill than the set you were comparing them with.

Call MSC at (800)645-7270 and ask for a free catalog, or go www.mscdirect.com and search for 'screw machine'.

&gt;&gt; What are they used for?

One use is the exact situation you have, where a normal length drill won't fit in the space available. The other, as Stepside noted, is that they are stiffer, which sometimes means that you can omit using a pilot drill or center drill to start a hole.

&gt;&gt; Why are they called "screw machine bits"?

There is (or was, CNC may have displaced them) a class of turret lathes called automatic screw machines. If using the shorter, stiffer drill meant eliminating the pilot drill, that would save one position on the tool turret, which might eliminate a second machine setup, which would be economically significant if you're making a bazillion pieces.

[Rotate]

Uncle Dunc,

I've sourced reasonably priced screw machine bit. Needed to compare apples to apples. Thanks.

Ablert