Thats how I did the wheels for my engine to machine the inside of the rims where the park brake rubs. (They are 2 foot diameter). Holding a 3 jaw chuck in a 4 jaw chuck also allows you to easily centre it.

Paul

So that's how preserved railways keep a wheel lathe in work, when business is slack!

Howard

Similar to Bill, I've used Unimat chucks in both Myford & Boxford lathes; I turned up a flanged mild steel spigot with M14 x 1 thread on it and the setup is excellent for gripping little fiddly things that can't easily be held in bigger chucks.

Yes I did exactly that, on spec, at Doncaster show a couple of years ago, got it home then realised mine's a Simat, so 14×1.4mm

Yes, I've now made one that fits, the main advantage for me is that the jaws are smaller, so they fit and expand into smaller holes.

Bill

No. Always double check it. Its usually within a thou or three but no guarantee. 

Edited By Hopper on 17/03/2020 00:55:07

Good point!

Hard to tell from the first pic. The second looks like a 4-jaw though.

First one looks like a self-centring 3 jaw in an independent 3 jaw.

The main chuck seems to be an independant 2 jaw to me.

Nigel B.

In the top picture it IS difficult to see but there is another jaw at 90 deg clockwise from the one that's obvious. You can just about make out the lines across the jaw steps if you look closely.Just ba pity it's all the same colour of muck and rust all over with flat frontal lighting.