I have been experimenting with lots of ways to turn pots. I am forever trying to minimize wasted wood. A glue block uses very little waste of the blank but it takes extra time waiting for glue to dry or risk things letting go. Also you have to waste your block over time. An expanding mandrel has very no waste but there were things I did not like about the method. I tried a face plate to turn the inside of the pot but the screw holes on my face plate are in a bad position. I used the nova screw chuck but those threads are meant for larger pieces and are very aggressive causing blow out around the center hole. Similar to Marvin's suggestion of the PSI bottle stopper chuck, I came up with this apparatus for chucking pots using my 70mm jaws, a "waste" block, and a 5/16" bolt..
First I mounted a piece of scrap oak on a face plate and turned it true. Next I drilled a 5/16" hole using my tail stock (to fit a 5/16" bolt through it). There is a 1" hole that you need not pay attention too. I then turned a socket to fit my 70mm jaws for holding with expansion.
To use it:
I lay out and drill my blank. Drill my center hole 17/64" which is the appropriate size for threading in the 5/16" bolt. Then I wax the bolt where the threads go into the blank. Then tighten the bolt into the center hole of my pot through the back of the mounting block. DO NOT SKIP THE WAX OR IT MAY BE A BEAR TO REMOVE YOUR PARTLY TURNED CALL! Now I can mount the entire thing on my 70mm jaws and turn the inside of the pot.
Originally I was going to just leave this mounted to a dedicated face plate but I thought, "self... If you turn a socket on one side you will not longer need to change from face plate to chuck". So I did that. This is the reason for the 1" hole. It was to recess the bolt head and leave room for a socket.
After I tun the innards of the pot, I remove it from the jaws and remove the bolt. Then flip it over and hold it under the slate ledge with the 70mm jaws to turn the back. I also drill away the threads left in the center hole at this point.
If you do not have a 4 jaw chuck you can use this method with a face plate and turn the inside of the pot using the bolt and flipping it over and jam it back on the "waste" block. Maybe even use the bolt to turn both the inside and outside. I prefer to remove the threads by drilling the center hole larger after I flip it and turn the back so I would go the jam chuck route.
You can use different size bolts to fit your needs. Just drill the matching size hole through your mounting block and the appropriate size center hole in your blank to take the threads. I caution not to go too small with the bolt as it could break or not have enough thread to hold. The I have tried a 1/4" bolt successfully. That is as small as I dare go and I am not 100% sure it will continue to work. I would suggest a 3/8" bolt for security sake but for what I wanted I needed a 5/16". Someone else might know more and be able to elaborate on safe sizes.
