Metal Lathe Chuck Capacity

Just thought I would throw out this question. Is there anything wrong with the threaded direct mount chucks? There seems to be a lot to look out for (and mess up) when trying to machine a

(sorry still getting used to this laptop and I keep hitting the wrong key for some reason)

So there seems a lot going on when trying to machine a backplate.

Besides the direct mount threaded chucks being more expensive, is there any reason not to buy one? Are there any adjustments or additional machining I would need to do on the direct mount chuck? I don't plan on getting another lathe, so this chuck would be a long term invenstement.

Thanks

The advantage of the separate mounting plate is that you must machine it in place. That makes it dead on concentric and perpendicular with the lathe axis. With a direct mount chuck, you have to depend on the maker of the lathe and the maker of the chuck to both have done their jobs perfectly in order for the result to be dead on. That'll rarely ever be the case, and correcting the tolerance build up will be much harder than just machining a separate backplate.

Gary

I bought a plain-back Bison 6" 4-jaw from Enco ($155.75):

a 4"(*) 1 1/2 x 8 back ($42.45): I had not done any lathe work since high school 45 years ago and I machined the back no-problem. I was a little intimidated, but it was pretty easy. If the advice in this thread isn't sufficient there are archived threads on Google that are very good.

• - the Bison chucks (well, the 4-jaw anyway) use a back plate much smaller than the chuck itself. For my 6" chuck, I used a 4" back plate and turned it down to 3 1/4". If you start with a 6" plate, you'll have a lot of turning to do.

Bob

You already have answers to the fact that the chuck that you mount yourself is more accurate than one factory-fit for a machine with the same spindle thread (but not your *personal* machine) is likely to be.

Also, bear in mind that the register diameter may need to be tweaked. This is easy with a separate mounting plate (and I've mentioned elsewhere in this thread at least one easy way to do it).

But the other consideration is that even if you are going to keep the same lathe the rest of your life, you may still want to change the spindle.

My 12x24" Clausing came with a threaded (2-1/4x8) spindle. I wound up replacing it with a L-00 spindle from another Clausing headstock from an eBay auction.

The reason for me wanting to do this is that sometimes I run the lathe backwards -- internal threading to a shoulder, or boring to a shoulder.

With a threaded spindle, there is a risk that the chuck will start to unscrew. With a L-00 (a big taper, with a key to drive the chuck, and a threaded collar to draw the chuck up onto the taper), there is no chance of the chuck unscrewing.

Now -- I had four chucks at that time.

1) 3-jaw with two-piece jaws, and made to fit a 2-1/4x8 spindle. (It came with the machine.) 2) 6-jaw with adjust-true feature -- which I had to fit to a backplate before I could use it. 3) 10" 4-jaw -- which I had to fit to a backplate before I could use it. 4) 6" 4-jaw -- which had a backplate for a 1-1/2x8 spindle, and which I was able to bore out and re-thread for 2-1/4x8.

Guess which of those I am no longer able to use? :-)

(Oh yes -- I also had to make an extension to the collet drawtube because the L-00 spindle was about an inch longer. :-)

Enjoy, DoN.