Thanks for the comments, Andy and Pete. Having turned the disc, I made a cradle for it out of scraps of plywood. The disc sat flat on the cradle, resting on its turned 'rim' to keep it stable. Then I simply screwed 4 pieces onto the plywood, one each at 3,6,9 and 12 o'clock....this held the disc flat and stopped it slipping laterally. Finally, I screwed another piece of ply over the top, to sandwich the disc.....so the disc was now captive in a plywood box. I then marked out the 'V' on the plywood and cut it on the bandsaw, then removed the disc from the box. Cleaning up the saw-cut was done with the timber held on the lathe, using a 2" bevel-edged firmer.
The blackwood plinth was easy...I just covered a piece of blackwood in masking tape, transferred the measurements of the 'V' slot onto the tape, cut it out and cleaned it up on bench-sander/linisher (horribly dusty, though).
Great fun...but took a few hours to get it done.
When the plinth was finished, I stood it on a bench drill press and drilled right down through it, with a clearance hole for a 4" number 10 woodscrew, then counterbored the underside of the plinth for the screw-head.
Les
