The physical size of any transformer coil bobbin (spool) over,
say, 50 to 100 VA is a bit large for winding with a kludge using a VSR
drill and some kind of "live center" bearing arrangement, even if beautifully-made.
A VSR arrangement might do for small transformers, especially, say, a 1/2"
VSR drill. Someone who does not have a lathe, does not anticipate ever
getting one for financial reasons, or lack of space, or unwillingness to
store such a large thing, if rarely used, anyway, might consider home-brewing
a "Transformer-Winding Lathe" using, say, a DC gear-motor, some sturdy
plywood for mounting it all, a couple of good ball-bearings and a fitting
axle, to act as a "live center". Then, add a DC speed-control. Dayton Manufacturing
has a line of 90 VDC gearmotors with controls, which would do such a job
just fine, with some mechanical wizardry and a few nuts-and-bolts tools.
But, especially as I have made transformers on up there beyond 750 VA,
I like a standard engine-lathe for this purpose. Two reasons for this:
It's there, anyway, as I use it for "normal things", and I rarely have
to "tie it up" for making transformers.
A wooden winding-spool such as illustrated herewith is easy to make
with basic woodworking equipment Or, one who "doesn't do sawdust" can go
next door to the ol' boy who does, with a sketch in hand. These sketches
should indicate rather exactly what is needed, and tiny details are left
out for the obvious reason that many will be making these "one-time-use"
items of "whatever's on hand", or, will have their own opinions as to what
is best, and will be doing it slightly different, anyway (perhaps only
to find, later, that they would have been much better off to follow the
sketches and instructions more exactly?).
A 3-jaw chuck in a lathe clamps easily onto a hex nut, so, the arrangement
shown with a length of all-thread with a hex nut on either end of the spool,
with one end of that all-thread center drilled as indicated to fit the
live-center is wonderfully straightforward and nonsense free.
Whether an engine lathe, a home-brew lathe, or a "VSR on a board" is
used, some means of turns counting is necessary. Thirty or more years ago,
even very professional coil-winding machines had mechanical "odometers"
for counting turns. These don't seem to be readily available as separate
or replacement parts, and if they are, they are probably very expensive.
Besides, one must be something of a mechanical wizard to arrange a reliable
cam and/or lever means of driving one of these mechanical counters reliably,
especially UP and DOWN. But digital ICs make the brewing of one's own UP/DOWN
counter rather straightforward, and readily available Hall-effect sensors
which look like TO-92 transistors, plus a small magnet, make turns counting
easy. Accompanying sketches showing how these Hall sensors and a magnet
were applied to the left end of my lathe's spindle should indicate how
one might do it for some other kludge, such as the home-brew coil winder,
or even the "VSR on a board" kludgery.
Jan
Rowland