Water absorption of secondary coil forms

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Rothman, Aric" <Aric.Rothman-at-Honeywell-dot-com> 

I recently made a secondary using a 3" OD phenolic impregnated cardboard 
tube.  At first, I planned to not bake the tube
to dehydrate it, expecting the phenolic impregnation would prevent 
significant absorption of moisture.  In the end, I'm
glad I did.  I weighed the 3"x20" tube prior to baking and after (140 def F 
for 10 hours).  The tube shed 10g of mass
during the baking process.  It was then immediately hosed down with aerosol 
insulating varnish (probably a type of
lacquer, actually).

The spray used is a common type used to impregnate motor windings.  I think 
its use was the source of my next problem.
I applied a coat of "short oil" (high resin content) varnish over the cured 
lacquer, leaving it to cure on my motorized
winding jig.  Eight hours later, the varnish had buckled in a very ugly 
fashion (orange peel doesn't begin to describe
it).  I suspect the application of the varnish over the lacquer was the 
reason for this failure.  I will uses shellac to
pot future windings before applying coats of varnish.  Varnish over shellac 
is a common woodworking finish combo.

I bake the varnished coil to accelerate the cure, sanded, and applied 
Pour-On epoxy finish, thereby making the coil
semi-respectable.

Aric