Lathe four jaw chuck

[Burnerman]

OK, nothing rare about that......but I found one today which was self centring!
In 40 years of engineering, I've never come across one before.
This one was made by Pratts.
John

 

[Jackrae]

They have their uses but are extremely limited in that you only get a good grip if the work is perfectly "square" on cross dimensions

 

[Dave54]

I think that I actually have one here. It's with a little Drummond lathe, but the thread's wrong for that so it's been in the cabinet underneath for the past umpteen years. I wanted a normal independent four jaw a while back for something, and that's when I found out it wasn't.
I know the woodturning boys use them with dovetail jaws to allow them to re-centre bowls etc.
Incidentally John I left those welder voltages with your comments.

 

[Burnerman]

Much obliged Dave!
John

 

[Burnerman]

I guess the accuracy of these things will depend on scroll wear, at the end of the day.....a bit like the three jaw option!
John

 

[Dave54]

Bound to be. That's the weakness with all scroll chucks. Self centering four jaw's handy if you want to hold square or octagonal I suppose. Round you can obviously hold with the 3 jaw. Neither's that much good if you need to accurately re-centre stuff. When I learned turning it was all done with a four jaw, or centres. I'm certainly no expert though. Few weeks some years back.
And then the bits I've done myself with that basically worn out Drummond.