I built this extended jaws fixture for holding bowls while finishing their bottoms a few months back. It has worked well for me when I had only eight of the tapered holding buttons. The problem was removing the extended jaws and the holding buttons and then screwing the buttons into the proper holes to use the jig with 8” and smaller bowls. To combat this time consuming configuration change picked up more buttons and 6mm mounting screws at Lowes. I can now leave the outer row of buttons in place for large bowls up to 12 1/4” and an inner row in place to hold an up to 8” bowl in place.
By moving just four of the buttons to the holes nearer to the center can hold smaller bowls down to 3 1/4” inside of their openings.
This pic shows an appx. 8” bowl mounted and the little bowl which was mounted in the last picture. Did not have to move any holding buttons to mount it.
This is a 11 1/4” bowl mounted. Again did not have to move any buttons to mount it.
This pic shows the original jumbo jaws and with the jumbo jaw extensions and buttons in place. The jaw extensions are made from 1/8” aluminum plate and drilled with additional rows of 6mm holes. The inner rows of holes must match with the holes in the original jumbo jaws. The jig stays mounted to an older 4jaw chuck.
This is a great time saver for me as it was taken 15 or 20 for all the reconfiguration for different bowl sizes. I have not thrown a bowl from this setup yet (knock on wood). I think it is due to the tapered rubber holding buttons. Good luck with yours and questions are welcome.
-- I,ve had amnesia for as long as I can remember. Vernon