When to grind the jaws in a chuck

bill70j said:
I guess I'll add one quantified data point.

I got an old 3-jaw Cushman chuck along with an Atlas lathe I purchased off Craig's List. The best TIR I could get was 0.008", and that was not repeatable. One could clearly see daylight between the chucked up part and the front of the jaws.

After in-place grinding, that TIR is down to 0.002 - 0.004"
Click to expand...
Wow, that's a real improvement!
Maybe I'll rethink things on that old one I've got!
 
I guess I need to include the project that prompted this question. I am working on a Sheldon 13 inch lathe with a taper attachment. The headstock dials in true. Sheldon lathes have a odd size morse taper.[I've read it to be a 4-3/4 if there was such a thing] in the headstock. I am attempting to make a few blanks to fit that headstock taper. Unfortunately it is the only lathe I have access to. This means I am turning the piece, removing it from the chuck, removing the chuck, test fitting, remounting the chuck , returning the blank to the chuck, Adjusting the taper , and turning again. All these moves, bring in errors . So I end up,, chasing my tale, until I get lucky, and one fits. Only to find that the taper setting that just made that "good" fit does not duplicate. Too much error in the chuck. I guess I will have to use the four jaw. It just got me wondering , How bad is too bad?
 
Joeman77 said:
If you grabbed it by opening the jaws are they still square when they close? Sounds like your method should work great with the Dremel, I've got something like that on my build-list too!
I had thought about doing this with an older Chinese chuck I've got laying around, but decided it was a little too sloppy for anything but a weld positioner, which I have yet to build.
Click to expand...

Eh. Close enough. I just made sure I didn't grab it too tight.

Huge improvement over how they had been, so I chalked it up as a win.
 
Why do you have to remove the piece from the chuck? I have made backing plates where I leave the backing plate in the chuck. I take the chuck off with the backing plate still in the chuck. Then screw the backing plate onto the spindle. I did the same thing when I made a spider for the outboard end of the spindle. Never took the spider out of the chuck until it fit on the spindle. Why can't you do that?
 
I have to remove the piece from the chuck to "feel" the fit of the odd morse taper in the headstock. With the chuck still attached it would be to heavy . I tried to get a good measurement of the taper but that is also a challenge. It is only about 3.25 inches deep. the major diameter is easy but getting the snap gauge at the precise depth for the minor diameter , is not so easy. Then there is the "fudge " factor . using snap gauges . And checking the fit with blue chalk .
 
Yup I read that post before, it has some information , mostly that the taper in the headstock is not standard. I used the four jaw today dialed in a taper from a blank that fit , then removed that blank and installed the one that did not fit and recut it. So I got the job done. I also built the grinding jig for a electric laminate trimmer . It worked great. I can for see me using it for other projects. like chucking 1/4 in shank end mills or burr bits in it. The three jaw now dials in fairly good so now I am happy with it. Thanks to all for the input .
 
You must log in or register to reply here.
Back
Top