You inquired about cutting gears for music boxes.  I must admit that
I am not an expert in cutting gears, nor do I have a machine shop,
however I have had to modify gears to fit into a music box more than
once.

I'll try to answer your question in a broad sense.  Starting with a
cylinder music box.  There are to my count 9 gears in a cylinder music
box.  The first gear is a ratchet gear for winding the spring.  This
gear is not highly critical in its shape or size, only that the two
winding pawls be able to hold it in place and that the square hole in
the middle sits squarely on the post for the spring.  This gear can be
cut to clock standards and should have a jagged tooth.

The next gear is in the spring barrel itself.  If a tooth is bad in
this gear, it is recommended to cut a similar tooth (teeth) with an
anchor and weld it in place in the barrel.  I have not had the need to
search for replacements of this type, but you might be able to use a
clock barrel housing if you can find the same size.

The third gear is a small diameter gear on the left side of the
cylinder.  Its teeth should mate with the spring barrel, so with the
post inside the cylinder (note that they are almost never truly
square!) to the spring, the size of the gear and shape of the teeth
should be defined.

Fourth gear is the large gear on the right side of the cylinder.  This
gear is the most complicated in the group as it has a groove on the
right side with an indentation for the tune-start/stop lever, it also
has a small gear mounted on the left side (between the gear and the
cylinder) that has a stepped incline to change the tunes (called the
snail gear--the fifth by my count).

The last three gears are in the governor.  The first gear is a simple
reduction gear.  It has 2 parts--a steel pivot and a brass gear.  The
brass gear is gently mated with the pivot.  The size of these two gears
changes from box to box and I've seen gears with such a broad range of
diameters that it would be best to measure it.  The second gear in the
governor is called the worm gear.

This delicate gear can be ordered from Nancy Fratti with the dimensions
of the old gear.  The shape is critical as it turns the endless gear
and there must be a perfect mate.  The endless gear (or worm) has the
fan on it.  This gear can also be obtained from Nancy Fratti.  You may
have to machine down the height to make it fit your box, but it appears
easier to me to order one than build one as the cuts are in a spiral.

If you're talking about a disc music box, none of the above holds true
except for the governor information.  One thing to note is that I have
two Regina music boxes and both of them I had to have the winding gear
machined for me.

Good luck,

Eliyahu Shahar