Four jaw chuck VS three jaw

A well-maintained and properly built three jaw will get you close to centered and concentric. With a four jaw, you can get dead nuts on.

Or, you can adjust a four jaw so that you can turn that barrel with bore that isn't concentric with the barrel, and make it so.

Or, you can adjust a four jaw to make eccentric turnings like oval approximations, for those special jobs.

Or, with a four jaw you can mount an irregular workpiece on the center you choose.

Think ultimate workpiece placement, and that's a four jaw. The best three jaw will only center a workpiece, at best.

A good 4-jaw chuck is just about a must have. As SJ mentioned you can center an off center barrel and turn non round objects. I have not been impressed with either of the two chinese 4-jaw chucks I have had. Try to find a good made in the USA chuck if you can. I have a very old and well worn cushman chuck that is still much tighter and smoother than either of the two new chinese ones I've had.. You can sometimes find fantastic deals on plain back chucks because the backing plate on them is some odd size. You can replace the back plate or even make one out of a 10-25lb exercise weight to fit your machine.

Agree completely! I posted a thread about my 4-jaw purchase a while back.

I agree with moleman. Be it three or four jaw, if it is sloppy it is useless. When I used to use my dad's lathe it was so nice to feel the key turn smoothly as you tightened or loosened a jaw. The less you have to "fight" the chuck the easier it is to center something.

I've only used my four-jaw three or four times in 18 years. But when you need it, you *need* it. If the price is sensible, you might buy it even if you don't have an immediate use for it.

Centering a workpiece in a four-jaw can lead to inventing your own swear words at first, but the old-timers are right - once you get the knack, it's almost as fast as a three-jaw.