Bruce Miller is correct in saying the best way to replace a wooden
barrel drive gear is to use a composite piece of wood so that the end
grain is more or less uniformly presented to the worm drive.  I find
beech is an excellent wood.

I am sure there are other suitable woods with a compact hard grain that
also possess good 'bearing qualities'.  I make a half-lapped cross and
then glue in the four right-angled pieces of Beech with the grain
correctly aligned before turning the gear wheel and cutting the teeth.

The brass worm wheels wear faster than the wood simply because the
surface of the wood is a receptacle for abrasive deposits and acts
just like sandpaper.

The brass worm can be repaired easily.  As the ends are rarely
in contact with the wood gear they retain their original profile.
A new piece of metal (often brass) can be machined to this profile
to replace the worn section and soldered into place using a spigot.

An article on this subject appeared in the Music Box, (MBSGB Journal,
Vol. 19 No. 6, Summer 2000).  The article describes a step-milling
technique using a small lathe with dividing attachment to form the
new worm profile.

Paul Bellamy