Here's something I knocked up I still have to grind the weld down and give it a coat of paint but even if it doesn't look very pretty it does a great job of pressing the rings when I glue them together. It completely eliminates any problems of the rings twisting or sliding about as they are clamped.
Made from 30mm and 25mm angle steel it is tall enough to take a 20 inch stack of rings and a ring 17 inches in diameter way more than I make at the moment, but you never know I might be able to afford a better lathe sometime in the future.
If you want to make one of these for yourself the materials you will need are.
10 ft of 30mm angle steel 3mm thick
8 ft of 25mm angle steel 3mm thick
2 foot 4 inches of the coarsest threaded 1 inch rod you can get.
4 nuts to fit the rod thread. 1 flanged housed bearing to fit the rod diameter. A piece of old kitchen work top and 2 bolts long enough to go through the work top and the flange.
When I made this I made the top and the bottom frame first, making sure that they were perfectly square. I then stood these on the side and laid the upright pieces into place making sure that they were perfectly square to the frames top and bottom. I then clamped a piece of wood across them and welded them into place.( you will need at least a 90 amp welder to do 3mm steel) I used a mig welder with plain co2 gas it spits a bit but not to bad. I then turned the whole thing over and did the same with the other side.
Across the top frame there are 2 bits of 25mm angle steel with a nut welded between them exactly in the middle, not easy to see in the pic. This is to take the threaded rod for the up and down movement. I then made the bottom insert and the top pressing board, you will need to cut 2 parallel sides a bit smaller than the width of the frame to enable you to get it in. Try to keep the other side nice and tight to the other parallel sides this will then prevent any twist when tightening down. The bearing is secured using the grub screw in the bearing, I also put a nut down onto the top of the bearing just to make sure it didn't get pushed up the rod. This is secured to the bit of kitchen work top with 2 2inch bolts and nuts, the bearings main purpose is to stop any twisting as it is tightened down. This coupled with the good fit in the frame does the job wonderfully, I have managed to glue 4 rings at the same time with absolutely no movement at all.
Knock up a handle and there you go. I would have like to use a piece of 40mm plexiglass for the pressing board but it was just to expensive, so I cut four slots in the pessing board to help me line up the rings in the centre, it works.
Have a go and make one for yourself it really save a lot of aggro trying to use clamps.