This is the crude system I use.  Make a rectangular piece from wood, 
fiberboard or plastic the desired size of the inside of the coil and the 
same thickness as the desired coil.  Drill a 1/4 in hole through the 
center of the form.  Now make two side pieces of the same material 
larger in area than the finished coil, again drill a 1/4 inch hole 
through the centers.  Wrap the 3 pieces with waxed paper or cling-wrap 
(either works fine), put the sandwich together using a 1/4 inch bolt and 
nut and tighten.  Hold the form in one hand and wind the wire on with 
the other hand.  An assistant to manage the wire spool and feed you 2 - 
3 feet of kink-free wire at a time helps.  Every dozen turns or so add a 
drop of fingernail lacquer to the coil to stabilize it.  (Q-Dope would 
be better but I don't have any - the fingernail lacquer works adequately.)

You can mechanize this by chucking the bolt end in a variable speed 
electric drill and clamping the drill to a table.  But I was able to 
wind a coil by hand in about a half hour.

Once you have the desired number of turns, let the form dry overnight, 
then take it apart.  The coil is supposed to separate from the form 
easily.  Set the coil on a piece of 1/8 inch lucite, perspex, acrylic or 
whatever, plastic - mark the outline on the plastic.  Drill some holes 
and finish with a rat-tail file to make a hole the coil fits in snugly.  
Glue it in securely with more fingernail lacquer and you're done.  If 
you left a tab on the 1/8 inch plastic use it for mounting the coil.

An advantage of this scheme is that the finished coil is only as thick 
as the coil itself - no bobbin walls.  This means you can use a smaller 
magnet gap than otherwise.  I use a 500 turn coil in a Chapman design 
magnet assembly and get 15 N/A as a feedback forcer.  I could easily 
double the force constant by reducing the magnet gap, but this is fine 
for my purposes.

Chuck Burch

PS:   I used clear fingernail lacquer but colored would brighten things up.

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)