Here is what I built out of some scrap exercise equipment metal, a support tube from old lathe and a 1" x 4" coupling which I had to purchase.
I used 3/4" bolts for the pivot hinge and the tubes slide in and out of each other for larger diameter turning. When the 3/4" bolts are tightened down it is solid as a rock. I put some weight on the tube at the bottom but probably don't need it. It allows me to turn from 20" to 44" diameter outboard. The test piece in the picture is 22" x 5/8" thick. The 1" coupling accepts Powermatic tool rests. If your lathe uses another size, they are available from Surplus Center.
The old lathe I started on is now a buffing station since the tube is now repurposed. Since the photos were taken I shortened the end of the tube that pivots 4" so the tube that slides into it will slide in further and get the tool rest closer to center.
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