But the cylinder is just glued to the cone, take it off any mandrel and
there is nothing to stop it going just slightly oval.
Temperature changes, humidity changes, self weight in use etc and I only
come across a coil/cylinder rubbing in the magnet housing after abuse.


If you wind the coil with a mandrel inside of the paper cylinder, and
bond the coil to the cylinder with something ( adhesive? laquer?
polyurethane?) when you're done, I would think that the wire would add
significant rigidity to the otherwise flimsy paper.

If you're still worried about deformation, leave the mandrel in the coil
while you glue the cylinder to the cone. Then there is no way it will go
out of round, short of gross mechanical injury.

Just a thought.

Pete