[HBR] Making Coil Forms (was 'Re: HBR digest')

[hbr@mailman.qth.net]

I use a variation of Helmut's technique.   I mount the socket in a vice 
or chassis hole.  I put the pins into the socket -- they should be cut 
to stick up maybe 1/2" to 5/8" or so.   The holes in the base piece 
(fiberglass, etc.) are laid out not quite so carefully and drilled with 
clearance so they'll go on -- minor adjustments can be made if  
necessary with a file.   I use this base to press a piece of wax paper 
over the pins and down to the socket, then drip parafin wax from a 
candle to cover the wax paper.   Then put the base piece on top of 
the wax while it's still soft; ideally the wax does not come up into the 
holes but does seal them.   

The wax paper keeps the wax out of your socket; the parafin *really* 
seals things so no epoxy runs down there.

Now I pour epoxy onto the base piece, securing the pins and forming 
a permanent plug assembly.   You can do this with the form in place 
too -- that's the strongest.  Or just fasten the pins to the base and 
attach the form in a separate step.   I try to wind up with 1/4" or more 
of epoxy above the base; have never had a plug made by this 
technique give a problem.

Variation:  Forget the base piece altogether and just use 3/8" of 
epoxy above the parafin.   In this case I'd put the form on at the same 
time and alignment of the form with the socket will have to be 
maintained while the epoxy sets.   The wax will do that, if you use 
enough of it.

I always sand all the surfaces the epoxy will bond to with coarse 
sandpaper first.

Walt Hutchens
KJ4KV

> I used PVC tubing I found that was 1 5/16 OD.  The base is fiberglass
> sheeting similar to PC material but without the copperclad.  The pins are
> 1/8 OD and 5/32 OD brass tubing obtained at a Hobby/model shop.  The most
> time consuming part was laying out the pin spacing.  Careful measuring is
> importent if one wants the form to fit the socket.