View Full Version : Chucks and the minimum diameter they can grip

Tony Ennis
08-13-2011, 10:23 AM
My 6" 4-jaw won't grip anything smaller than 3/8" in diameter. I need a 3-jaw, so I figure to buy a smaller size.

Is there any rule of thumb on the lower end of gripping capacity?

08-13-2011, 10:53 AM
Just get more pointed jaws for your chuck.

08-13-2011, 10:56 AM
Or, make pointy soft jaws.

Or, get a collet chuck instead of a smaller 3-jaw. It'll have less runout than a 3-jaw if mounted carefully and you get good-quality collets.

08-13-2011, 10:57 AM
My Bison 8" 6 jaw will grip down to 5/16". For anything smaller I use a drill chuck mounted in a 1" solid socket.


08-13-2011, 11:11 AM
Buy a 3" chuck, and chuck it in your 4-jaw chuck.:D

08-13-2011, 11:15 AM
I used to chuck a Jacobs type chuck in the big chuck to grip real small diameters. You can still indicate the part in to get it to run true. I mean the type of Jacobs chuck you use in the drill press,or tailstock.

Now I have another lathe for smaller work(Hardinge HLVH) that uses collets.

08-13-2011, 11:53 AM
My Bison 8" 6 jaw will grip down to 5/16". For anything smaller I use a drill chuck mounted in a 1" solid socket.


Take out every other jaw in a six jaw and the jaws will almost meet.

08-13-2011, 03:02 PM
It isn't a six jaw the OP is describing,though.

08-13-2011, 03:28 PM
This is my 250mm (9.84") Pratt Burnerd Super Precision 3-jaw scroll chuck. It' seems to be able to hold down to somewhere around 4mm (.156") quite securely. And, near-zero runout no matter where it's measured.

It was sold to me by a former employer for $250, never had been on a machine.


Forrest Addy
08-13-2011, 04:28 PM
A friend of mine sculpted out a set of soft jaw for his three jaw so it accepts 5 C collets. Works pretty good and he saves several hundred $.

Chucking a 3" three jaw in a larger 4 jaw works well for small sizes too. You can adjust the 4 jaw to exactly center the three jaw.

I suggest bolting the three jaw on a disk of 1/2 thick round stock made to fit but having a 1/4" larger OD for the 4 jaws to grip on. The disk takes the abuse of the jaws and not the smaller chuck body.

I have a couple dozen split bushings I've made over the years for different things including a number that have been tapped. I slip them in the three jaw for smaller work or bolts I have to grip to mod the head.

08-13-2011, 09:24 PM
For really tiny stuff, I've put the small rod in pin vises and then chucked the pin vise in the lathe.

J Tiers
08-13-2011, 10:59 PM
Forrest has it......

That's what they make collets for