H. P. Friedrichs wrote:

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.

Hi...

Used to do this way back in the olden days (just shortly after
they invented sunshine so let me throw in my 2 cents in the
hope it may be helpful.

First, though, never ever created voice coils themselves. On a rare
occasion replaced one. Much more often replaced cones that had
been penetrated by little fingers, tools, or just dried out and
cracked.

A thought, if I may? Don't think I'd glue the winding to the
form; might rather consider shellacing it in place, while the
whole thing is still on it's solid form. Use a spray can; that
way you'll stiffen the paper form as well.

Don't think it matters much (if at all) if the form does go
slightly out of round while it's "in hand" What has to be done
is find pieces of paper that will fit perfectly between the
magnet and the newly wound coil and it's form. Has to be just
right - tight enough to firmly hold the coil in place, yet able
to be pulled out without damaging the coil or form.
(remember that the coil has to not only be centered, but also
temporarily hold the coil at the proper height - so that it
won't hit bottom or come free of the magnetic field when the
cone moves)

So, experiment with paper weights, find ones that can fit just
snuggly enough. Cut yourself a number of pieces, 'bout 3 or
4 inches long, 1/4 inch wide. Drop the coil in alone, look
with a flashlight and magnifying glass to see what it looks like
bottomed. Take it out again, insert it with the paper shims all
around so that half of the free space you just saw is now free
again with the shims in place.

Now glue down the outer circumference of the cone, and spot glue
the voice coil to the cone at 4 equidistant spots between the shims.
When this glue is firmly set, remove 4 more shims at 90 degree
seperation, tack the newly freed spots. Keep this up until the
shims are all out, and the coil is firmly held all around its
perimeter.

Install the dust cap, and you're done

Take care.

Ken