Metal spinning

[Simpo Two]

I need to make a copper dome about 50mm in diameter. I have thin copper disks and a lathe, and from looking at it on YT it seems fairly simple. However I can't work out how they hold the copper onto the buck. They use a white block on the tailstock that slides up - how does that work? I was planning to use a couple of screws to hold the disk to the buck below.

[clockworks]

A live centre in the tailstock, with a reasonably soft pad?

[Simpo Two]

clockworks said:

A live centre in the tailstock, with a reasonably soft pad?

Thanks. I have a live centre, but not sure what the 'soft pad' could be. The central part of the dome is actually flat which helps.

[OutInTheShed]

The white block may be PTFE?