I have not had that exact issue but have had similar issues with shops that
won't work on things for liability or insurance reasons, or they are
clueless because they can't find a part or spec in their computer.
My guess is this is a newer or at least shiny and newer looking place, quite
possibly part of a chain.
Find a shop in a lower rent district that looks a little worn around the
edges, not piles of unfinished work and junk around, but more of a
The shop should be staffed by an older guy or guys over 50. He will look at
your drum, he will have an idea of what is acceptable thickness on this type
and size of drum and will turn it for you without needing to look at a book.
Or he may even have a book that has the spec in it. He has been in business
for a long time because he knows his work and is an honest craftsmen.
He will charge you a reasonable price for the job, he may or may not take
credit cards, so bring cash or a check when you pick it up.
Unfortunately these types of shops are getting more and more rare, but they
are out there.
I may be off base about where you went when they wouldn't turn the drum and
where you need to go to get it done, but if I am I will eat my hat.
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