Well, if you want the ‘official’ answer, there isn’t one. It depends
on the situation. In my most anal-retentive moments, I’d probably
file the bezel down a smidge until it was the right height.
(After it was soldered on, and using a fairly fine file, like #4)
That’d probably be the “proper” answer, in a world where time had no
meaning or cost.
On the other hand, I’ve seen all sorts of weird things inside bezels
that I’ve taken apart over the years. Sawdust, newspaper, curls of
wire. Pretty much anything can be used to jack the stone up. When I
do it, (not that I ever do) I tend to use snipped out bits of
plastic milk jug. The plastic’s stable and inoffensive. It also
won’t react to water or humidity the way the cardboard will, and it
doesn’t compress while you’re rolling the bezel. (Or so I’ve heard.
I wouldn’t ever do anything like that.)
Actually, I have taught pretty much exactly that technique (using
the milk jug bits instead of cardboard) to my beginning students,
for the following reasons:
(A) they were beginners, and I was trying to get them out the door
with a wearable ring in about 4 hours of contact time. Sometimes
much less. (Like 3 hours flat, including learning to solder without
setting themselves on fire.)
(B) I had one size of bezel wire for the whole class, and all sorts
of 50 cent gemshow special stones, which means that the thickness
and dimensions were all over the map. Any student could have had
any size stone. So I had to get bezel wire that’d take the biggest
stone I’d be likely to have to deal with. Anything else could be cut
down or jacked up to fit.
© To prevent failure. Remember, these were beginners. It’s much
harder to create a screwup that’ll trash their ring if you’re
jacking up the stone. In a class of 24 continuing-ed students, I can
absolutely guarantee that at least 3 of them will over file, or
otherwise trash their bezels if I try to get them to file it down to
the ‘right’ size. Which gets us into individually supervised repair
work, which takes time away from the rest of the class.
If I’ve got a smaller class, or a more predictable supply of stones,
I try to tailor it a bit more closely, but jacking the stone up,
rather than cutting the bezel down is what I do with a big class. It
sounds like your instructor is doing something similar.
Sometimes, the needs of the class take precedence over 'perfect’
technique. This seems like it might be one of those times.