View Full Version : Dumb Question about Four Jaw Chucks

06-25-2010, 01:00 PM
Okay, here it is: why do the jaws on smaller four jaw chucks close up entirely, and the jaws on 6" and larger four jaw chucks do not? I just bought a 6" chuck and can't grip stock smaller than 3/8".

06-25-2010, 01:05 PM
I think the sharper jaw tips needed to go below 3/8" would be likely to mar the surface you're gripping.

06-25-2010, 01:29 PM
Your question does not really make sense

First you mention 4 jaw chucks then compair them to 6" chucks?
4 jaw chucks come in smaller and larger then 6"
So do 3 jaw. And 6 jaw.. 2 jaw.. etc.

Most lathe chucks do NOT close completely.

Soft jaw (aka 2 part jaw) chucks can have jaws made that close completely, but they would mar most work and not hold stuff very well in a 2 or 3 jaw chuck.

For smaller items, Lots of hacks can be done. Iv chucked a pin vise before to hold a tiny item.. Or you can buy a 5C collet block ($10~20) and some 5C collets and chuck the collet block (or make a proper collet holder for the lathe..) Or you can wrap the small item in thin flexable sheet metal if its not too much undersize.

Chucking up a drill chuck to straight arbor adapator... Works, but is dangerious since JT tapers do not 'lock'

06-25-2010, 01:51 PM
My 3 jaw closes to a little over .125 so I had a lot of trouble facing some 1/8" brass rod.

I got a tip from the HSM magazine which I can't find right now or I'd mention the guys name.

Put an old chuck from a drill in your lathe chuck, then hold your small work piece in that. I tried it today and it worked but my drill chuck was in sad shape so not perfect but WAY better than what I was doing before!

06-25-2010, 02:38 PM
Black Moons,

My little Sherline four jaw closes all the way. My new 6" four jaw chuck does not. (I will edit my first post to be clearer). My Rohm 3 jaw chuck closes all the way. It is 6".

06-25-2010, 03:23 PM
Yep, it's all a matter of how wide the tip of the jaws will be.

In general, a larger chuck is expected to hold larger things, so it needs beefier jaws. A 2 inch chuck will not be holding anything wider than 1 inch, so it's jaws can be narrower.

To close down 100%, the jaws would need to come to a sharp point like a V. Very few chucks have such a design, as it would not hold well, it would be easily damaged and it would mar the work.


06-25-2010, 03:49 PM
Danlb: that makes sense to me now that you explain it. I wanted an independent four jaw, so I could indicate in small stock very precisely. I guess I'll look into alternative jaws for the chuck, or maybe a collet holder.

06-25-2010, 04:27 PM
how small is small? 3/8"? doable in a four jaw, you just need a small 4 jaw? Over the years i've collected different sizes for the reasons Dan mentions - smallest is a 2" (iirc) unimat cuck. Its an orginal and quite high quality - get one on ebay for a reasonable price. Make an adapter for the spindle taper or collet

....or make a block with an accurate 3/8 bore and a brass pad with a set screw behind it to hold the work. dial the block in on your larger chuck.

06-25-2010, 05:20 PM
3mm to 6mm axles mostly, but a lot of rod in varying sizes under 3/8". Can't get a factory collet tube closer with this iteration of the Super 11 (because of the larger spindle bore, I'm told) unless I spring for something like Bison's collet chuck. I thought I could get by with a four jaw until I could afford another major expenditure like a collet chuck.

I'm moving from a Sherline to a Super II with D1-4 Camlock. Kinda like moving from a balsa wood glider to an F-16.

06-25-2010, 05:33 PM
Smaller chucks generally hold smaller parts??:)

06-25-2010, 05:33 PM
My Clausing sports a 12" three jaw which doesn't close pass 1/4" and hold too well. When I need to, I will chuck-up my 4" three jaw that is for the Haas indexer I have. It is a 'set true' chuck and is very useful in both apps. I use it and and old Jet chuck on the mills also.
I recently 'e-bayed' a 3" three jaw which may get two or three arbors to use on several of my machines.

06-25-2010, 11:12 PM
Get a small 3 or 6 jaw with set true if you can. This way you can use it to hold parts and TIR it to zero runout when you need it to. Save the 4 JAw for holding square parts. If cost is extremely important just get a small 4 jaw, the jaws should be more sharp and close up more.

Ideally for turning with low TIR, especially on small parts you really should get a 5C collet set. The sets in 64ths will cover most sizes you can throw at it and is useful if you turn down a diameter on a part and want to flip it to do second operation work on the back of the part which may not be exactly nominal.

Don't do what I did and order an ER collet set to save money. The part has to insert into the ER collet a good ways in order for it to grip right which makes it unusable when you want to flip a part that you turned down a short section on. I'm going to be buying some 5C collets and probably a bigger lathe to take them in the spindle. CDCO sells a 5C collet chuck for $140, but you will have to buy and machine a backplate for it that is accurate to your lathe. You might also have to skim the taper of the chuck on your lathe with a grinding tool or carbide bit to get it perfect to your lathe spindle.


06-25-2010, 11:18 PM
You could get a straight shank ER16 collet holder in 3/4 diameter and a set of ER16 collets. Put the holder in the lathe chuck and the workpiece in the collet.
ER series collets have a wide grip range that covers inch and metric with one set. It's a simple matter to dial in the shank of the collet holder or the workpiece in the collet.

Robin R
06-25-2010, 11:43 PM
If going for an ER collet aetup, it might be worth going to ER29, ER16 does go up to 3/3", but that isn't much of an allowance over the minimum capacity of the 4 jaw.

You could just chuck the body of a drill chuck in the 4 jaw and center the work once the drill chuck is gripped by the 4 jaw. It's a bit of a cludge, but would get you up and running for now.

Herm Williams
06-26-2010, 12:06 AM
I have a 2" three jaw that I chuck in my 12" four jaw sometimes, put a 1/2 bar and indicate to the accuracy I want and go for it. I use pieces of copper to keep from marring the finish on the small chuck.

06-26-2010, 12:18 AM
Oh yea, another good trick is chuck whatever stock, drill it for the size you need (or undersize and bore to size for best accuracy), then slit it in a bandsaw or with a hacksaw, then grip it in a 3 or 4 jaw
Makeshift collet

06-30-2010, 02:23 PM
I disagree with Toolguy on the ER16 holder unless you want one to get for holding cutting tools on a mill or in your tailstock in addition to the work holding.

The problem with the ER collets is that the work piece needs to extend a fair distance into the collet for it to have a chance at tightening up. On a 5C or 3C collet (or morse taper) you can turn down short ends and grab them in a 5C chuck for doing a little light duty "back work" from a short parted off part (Think of a two discs stuck together.

You can do alot of this with a chuck if your jaws are not dulled at the ends, but ideally you would want a 6 jaw set true type so that you don't leave as deep a mark in the part as you could a 3 jaw (This is assuming something like a soft part, Aluminum, mild steel, etc). Again, a 5C collet would be better here, but alot of us on this board do have home workshop budgets and sometimes need a "one size fits all" kind of tool.

I'm saving my money for a 5C collet set, collet chuck (or bigger lathe), and a 6 jaw "set tru" chuck.

I might get the 6 jaw set tru first because I can use it as is for most of my home projects. A 6" unit will grip fairly large parts and the bore of the chuck will accept 1.5" stock which will allow me to work with longer pieces in that size range (my lathe only has a MT3 spindle with a 0.75" bore).


07-01-2010, 12:47 AM
I think that I will get a Bison collet chuck when moneys become available. In the interim, I'll get a collet block as was suggested by previous posters. Another thing I could do is try to chuck the little Sherline four jaw in the Rohm four jaw.