Hi Charlie

I think that would be a not so smart idea.

However there are fiber optic cables, and you could tape a bundle to
your tool shaft, and have light shine on the one end and bring the
light inside that way, another is low voltage bare bulb also taped to
the tool shaft to light the inside, but my favorite way is,
stop lathe, clean out shavings, measure, etc.,
Hollow forms are not for the hurrying ones.

Have fun and take care
Leo Van Der Loo

charlie b wrote:
Having just recently blown through the top of a turned lidded vessel,
and having noted that a light shining into the inside while looking
from the outside makes it semi-obvious how thick or thin the walls
are. But you can't put a light inside while your working on the inside
- duh. And it's kind of a PITA to turn the lathe off, get the tool
rest out of the way, stick the light up against the opening of the
hollow form then look at the piece from the chuck side.

BUT - You Can get donut shaped fluorescent light bulbs. And if
you can fix it to the drive end of the lathe - behind the chuck
or around the chuck - and made some kind of shade - then
you might be able to use light to tell you how thick the wall
of the piece your working on is getting. Could probably turn
a "shade" even.

Brilliant idea or a dumb idea?

charlie b