Mystery lathe collet

[LittleWatchShop]

Found this among my lathe accessories.  What is it used for?

[nickelsilver]

That's called a cement chuck (or cement brass, or wax chuck). There are small diameter ones like this and larger ones like little face plates. With these small ones you would use it to chuck longer pieces that can't be held conveniently in a regular collet, or when you need higher accuracy than what your collet can give. Fried has a pretty good writeup on them in the Watch Repairer's Manual. You drill an accurately centered hole, deep enough that you can fit the area you want to chuck on and maybe 50% larger in diameter than your part, with a nice sharp V bottom. The V will center the chucked end of your part. The brass is heated and filled with shellac, the part put in, then with the shellac still soft and with the lathe turning slowly, nudged true while the shellac hardens.

 

With the flat faced chucks you can cement and center flat parts.

 

The same can be done by just chucking up a piece of brass.

Edited February 28, 2021 by nickelsilver