Adjustable 3 jaw chuck

[jworman]

I've had a Atlas 10" with a threaded on chuck for many years. Recently I purchased a larger machine, a Clausing 12". The three jaw chuck is somewhat a clone of an adjustable Buck chuck. I don't think it's a Buck as there is no name on it, and a question to Buck indicated that they put their name on all of their chucks. It was probably made about 1951, when the lathe was built.




This is the first chuck I've had that has the capability for run-out adjustment. The other day I chucked a rod in it and put the dial indicator on the rod. I had a bit over .005 run-out, so I decided to see how to adjust it. I had already cleaned the interior, so I loosened the hex screws around the outer face a little bit, then started on the 4 hex screws toward the rear of the chuck.

It seemed logical that it should work much like a 4 jaw adjustment. I very soon saw I had run out of travel before I had moved the chuck much.

It seems like I need to take off about .010 from the shaft coming out of the adapter plate. It wouldn't be much and it seems to me like the chuck wouldn't notice the difference except I could move another few thousandths in the truing process.

My next thought was "hold on there, John. You may want to ask experienced people before you honk something up!"

Am I thinking to do something bad or does this sound reasonable?

 

[Tony Wells]

First make sure you are actually moving the chuck body. Use a dial indicator on it. Then pull out the adjustment screws and make sure the threads are good, and the ends not mushroomed out. There generally isn't much travel in an adjustable chuck. Possibly it has already been adjusted as far as possible in the required direction. You mentioned the face bolts being loosened, that is important.

I generally start off adjustment of a buck-type chuck by loosening all 4 screws, then pushing the chuck body around following the low spots. After getting it pretty close, make sure the opposing screws are snug. Treat it like a 4 jaw chuck.

If you can't get enough travel, the jaws aren't right. Might not be an original set, might have been damaged. Before addressing the mounting boss, I would look into grinding the jaws. Be sure to indicate the chuck body in before grinding the jaws. Last resort would be to machine the mounting boss on the back plate.

 

[jworman]

I will check all you mentioned. Winter has come to New Mexico (just a wimpy winter, but we are pretty wimpy when it comes to cold!) so it may be a day or two before I tackle this.

Many many thanks,

John