View Full Version : How do I mill down the end of a drill bit?

Benjamin Borowsky
07-22-2003, 10:57 AM
I am drilling a series of deep, wide (for the sherline) holes. I want to use a bunch of drills whose shanks are larger than 3/8", the max Sherline chuck size. Is there a way to mill down the shank on a lathe so that it'll fit in the chuck?

What I mean is, do I need carbide bits? Will HSS do it? Or is this a basic impossibility with this machinery? I'm trying to avoid buying a new set of bits, when the set I've got may do the trick.

Thanks in advance,


PS: In Sherline's documentation on carbide inserted bits, they specifically say you can't mill down a milling bit, so things may look a little bleak... but I'd love your opinion.

07-22-2003, 11:03 AM
You could use a tool post grinder in the lathe to reduce the shank diameter.

07-22-2003, 11:06 AM
I don't think the shanks on the average drill bits are hardened. That's why they get scarred and buggered up when they slip in the chuck. You should be able to turn those like most other steels.

07-22-2003, 11:11 AM
Ditto lynn. Even carbide drills are only carbide tipped, the shanks are machinable.

G.A. Ewen
07-22-2003, 01:33 PM
I have done this many times with no problems on large bits ( over 1" ). Chuck the drill buy the shank and center drill it, then chuck a piece shaft and drill or bore a dead end hole about 1" deep the diameter of the drill bit that you want to reduce. Put the drill in the hole, bring up the tailstock and just snug up a live center. You can now turn down the shank without difficulty. http://bbs.homeshopmachinist.net//wink.gif

Benjamin Borowsky
07-22-2003, 09:03 PM
Thanks, guys. As this isn't an expensive set to begin with, I'm sure I'll be ok.


"Chuck the drill buy the shank and center drill it"
I'm good so far, following you nicely...

"then chuck a piece shaft and drill or bore a dead end hole about 1" deep the diameter of the drill bit that you want to reduce."
Do you mean make a "female" part to insert the drill "male" part into?

"Put the drill in the hole, bring up the tailstock and just snug up a live center."
So the tailstock with live center is up against the "female" part, which is around the drill bit, which is connected to the headstock how? I think I lost you a few steps back. Could you explain it a little simpler for someone who usually needs a few explanations? Thanks.

"You can now turn down the shank without difficulty."
Yeah, that's what I'm looking for!


07-22-2003, 10:28 PM
Once you get the hang of it you will have turned down drill bits all over the place http://bbs.homeshopmachinist.net//biggrin.gif

07-22-2003, 10:45 PM
You don't want to crank the chuck jaws down on the drill flutes so make a socket to hold the drill. As the socket is the same size as the drill and the drill will bite the end of the blind hole, all you need is to center drill the shank end and apply a live center to hold it while you turn it down. Center drill the shank first by holding the shank in the chuck jaws.

[This message has been edited by Evan (edited 07-22-2003).]

07-23-2003, 12:24 AM

If I were you I would learn how to use HSS tools first and once you are a keener, then worry about solid carbide.

You can, if you look for them, buy reduced shank drills Silver & Demming drills are normally 1/2" reduced shank, but there are also 3/8" reduce shank bits available (the 3/8" shank oftern have three flats milled on the shanks to help prevent spinning the bit in the chuck. Check with the national line suppliers like Enco, Travers, J&L Industrial, KBC, or any of a hundred others. Get on line and order their catalogs, read them before going to sleep.

Take everything one step at a time... http://bbs.homeshopmachinist.net//biggrin.gif

P.S. Buy yourself a Rohm Keyless chuck and get rid of that cheezy Jacobs style key chuck - the keyless has greater grip on the drill shanks. Well worth the $50 or so they cost.

[This message has been edited by Thrud (edited 07-23-2003).]

Benjamin Borowsky
07-23-2003, 08:36 AM
Evan: Got it! Thanks, I didn't realize that the drill bit would bite on the end, so I didn't see how the whole thing was driven.

Thrud: Yah, I know there are reduced bits, but after spending all the money on the mill and the lathe, AND the drill bit sharpener so that I don't need to buy any more bits, I sorta didn't want to buy any more bits. I do think I'm going to take your advice and stick to HSS for as long as I can, though


07-23-2003, 10:21 AM

I too have a sherline and had the same problem...

I went to the hardware store and bought a 3/8 Jacob chuck with the same threads as the Sherline 1/4"

G.A. Ewen
07-23-2003, 10:48 AM
Hot off the press! a 7/8" bit turned to 3/4" shank.
www.photobucket.com/albums/0603/GAEWEN/7122d1f2.jpg (http://www.photobucket.com/albums/0603/GAEWEN/7122d1f2.jpg)

www.photobucket.com/albums/0603/GAEWEN/eb5c898c.jpg (http://www.photobucket.com/albums/0603/GAEWEN/eb5c898c.jpg)

www.photobucket.com/albums/0603/GAEWEN/5544da40.jpg (http://www.photobucket.com/albums/0603/GAEWEN/5544da40.jpg)

Peter S
07-23-2003, 11:06 PM
I think the answer to this question and others like it is - try it yourself and see what happens.
This is how you will best find out how to get a drill to run true, what speed is best, will HSS do it etc. The worst that can happen is you need to regrind your HSS - and thats good experience too.

Peter S
07-23-2003, 11:27 PM
The only problem I see with your method is...you can't drill the bush to size, because the whole problem is - the drill won't fit the drill chuck.
OK, you mention boring too, I guess drilling a smaller hole right thru' then boring a recess will give the drill an edge to bite into?

G.A. Ewen
07-24-2003, 12:58 AM
Peter S, There are probably many other ways to do this job. This one just happens to suit my needs and equipment. I agree that trying out different methods yourself is the way to find out what works best. http://bbs.homeshopmachinist.net//wink.gif

Paul Alciatore
07-24-2003, 01:47 AM
Peter S.

I've never done this but it seems to me that most large diameter bits have a generous shank length so there should be enough there to grip it in the chuck near the end of the flutes and still have enough sticking out to cut down. Likely a better grip than the cup holder. But doesn't this assume you will have a lathe with a 3/4" or 1" spindle bore? Not very likely to be in the home shop.

Another thought: I frequently have the same problem in my Unimat: 1/4" chuck but I need a larger drill or mill. I just mount them in the 3 jaw and let the chips fly. This works on the Unimat tailstock also (perhaps not on the Sherline though).

I also recently purchased an inexpensive 1/2" drill chuck and bored out the original threads and retapped to 12mm x 1 for the Unimat spindle. Again, it works on the tailstock as well as the headstock. Should have done this 30 years ago. Main problem now is buying shorter length bits (7" max between centers and the vertical column is not that tall either). They come in handy on the full size mill-drill also when changing from 2.5" long edge finder to a large diameter drill. All in all, much better than reduced shank drills.

Paul A.