Tuck a neatly laser-cut disk into a flimsy cardboard tube:
Put a big conical center in the tailstock:
Whereupon the tube remains nicely tubular on both ends and aligned along the chuck axis:
Which is why you save all that scrap material …
Yes, it’s the core from a toilet paper roll, which is way cheaper than burning through tumblers / mugs / shot glasses / whatever while figuring this stuff out.
The Smell of Molten Projects in the Morning 
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