Not really a chuck but it is designed to hold small flat washers when resizing them. I used aluminum for the outer shell and a large neo magnet for the power. To transfer the magnetic field to the flat washer to be turned I made up a brass and steel magnetic block. The center steel in the brass is just 1/4" rod from the hardware store, not drill rod. The other 8 pins are made from 16d common nails. They were just a bit small for a tight fit in the holes (closest size drill bit I had) so I knurled them to increase the diameter to a tight slip fit. After fit up I faced them in the lathe and then lapped the faces a bit with 400 wet or dry. Added some 271 locktite and that was it.
One note about the magnets. The plating is very thin and delicate. That is why the brass/steel transfer block was made. There is more holding power in the magnet directly but you run the risk of chipping the coating.
This "chuck" may be used from either side but if I want to protect the magnet then the brass side is the one to use.
These won't take a lot of stress but will work for a quick washer sizing. The nice thing is that they will fit in any of my chucks so I won't have to change the chuck just to size a washer.