Bruce L. Bergman wrote in message
...
On Wed, 12 Aug 2009 08:44:36 +0100, "N_Cook"
wrote:

In preparation for the next time (if) I do another one, as many thousands
of
turns I don't fancy doing another one, to explore this anomaly.
I successfully wound my first 0.05mm wire guitar pickup rewind, but one
curiosity- anyone know the reason?

This sort of rewind needs winding on a demountable former and
transfering,
as a hank of wire, into a trough. On demounting, there is a distinct
banana
shaped bowing to the hank
Hank is about 65mm long , place onm a table and the ends are , equally,
about 8mm off the table.
Possible reasons , I can think of
1/ there must be a twist in the
wire on the spool , despite pulling the wire off the supply spool
tangentially rather than
axially.
2/ some bias on left hand traverse versus RH traverse on the coilwinder
machine.
3/ For this sort of very fine wire,
instead of a final delivery pulley I use a tiny PTFE lump on a small bar.
A
hole in the PTFE squashed to form a sub-mm slot. Then a 15 foot run back
to
the spool (and a light felt slip clutch) to allow for any snatching.
Because
of room arrangement , to get a 15 foot run , the winder and so PTFE is
set
at an angle of 25 or 30 degrees rather than straight fore-aft. Perhaps
that
puts a set on the wire.

My totally uneducated guess (I am not a professional coil winder, I
deal with 12-GA and 14-GA solid...) is that there are residual
stresses on the wire from when it was wound onto the spool.

You might want to use a set of pulleys in series as a Straightener
after the supply reel (and felt clutch) to gently work the stress out
of the wire - you put five or seven pulleys in a sawtooth pattern so
the centerlines of the groove are only a few degrees off a straight
path, which makes the wire bend back and forth ever so slightly as it
goes through them.

One set of pulleys for vertical, then a second set for horizontal.
Then go through your PTFE slip block and onto the coil winder.

Oh, and is there any problem with putting a drop of varnish onto the
finished coil in several spots while it's in thew winding bobbin, let
it wick through and set, then remove it from the bobbin form?

Pick a resilient varnish that won't eat into the insulating varnish
on the wires and cause shorted turns (ask the wire manufgacturer for
suggestions, they probably have several...) and it'll be a solid form
coil but it could be bent if you need to without going "Sproing!"

-- Bruce --


Unfortunately the UTS of such wire is about 5 ounces, before any work/age
hardening or imperfections, so any more path resistance more than the
minimum will cause a break. The felt slip clutch for back tension at about 2
ounces was too high, wide brroke after 1000 turns, and I had to reduce it
to about 1 ounce. Not possible to dab varnish on before demounting. The
former has to resonably match the profile of the trough which is intenal
dimension about 60 x 3 mm , far from the normal circular form, and on top of
that the cross section should be square, but for practical reasons its not
possible to make the former square in section as the wire would catch on
edges while winding. So it is necessary to allow the windings to move over
one another to reform into the available space.