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Polyester Resin?

 * Original msg to: Froula-at-cig.mot-dot-com
 * Carbons sent to: usa-tesla-at-usa-dot-net

Quoting Don Froula <froula-at-cig.mot-dot-com>:

> Richard, just received my commercial cap from Scott and am 
> really itching to get things tidied up and throw the switch!  
> It's been just about one year since I first ran across an 
> archive of your excellent postings on basic 6" coil 
> construction.  To date, I have assembled all of the materials 
> needed to make the finished coil, passing up some "bargains" in
> favor of getting the correct component.  The goal is a
> nice, turn-key unit.  Thanks for all of your ongoing help and
> encouragement. 

> I have my secondary wound (6" OD acrylic form).  I have been
> experimenting with various coatings to seal the coil.  I would
> like to use an epoxy coating for better durability.  I tried 
> some fiberglass resin (the stuff used for auto body repair with
> fiberglass matting). By using slightly more than the recomended
> hardner, this stuff seems to work OK on my test windings on an
> old, cracked acrylic form.  I recently read your comments on 
> the unfavorable RF dissipation factor of polyester resin.  
> Should I look for another sealant?  I'd hate to ruin the 
> secondary at this stage of the game by using a compromise 
> coating!

I would. We ran the gauntlet of sealers awhile back. The problem
with the polyester in addition to the dissipation factor is the
brittleness and poor chip resistance. It also shrinks as it is
curing and I have had the coating crack as a result of excessive
shrinkage.

There are some oil/solvent based acrylic sprays out there, and 
there are some fairly liquid two part epoxies sold in cans that
can be brushed on. Polyurethane does not have the greatest RF
dissipation factor, but the fully cured coating offers
exceptional chip and ding resistance and the dielectric strength
is very good. You might look at some clear enamels too.

You can get the coil up and running without a sealer if you are
careful not to overcouple severely, and you watch that you don't
ding the windings. I have set up and fired an newly wound coil on
many occasions only to pull it out of service after a few "warm-
up" runs to apply sealer later.

BTW, this project sounds awesome. Be sure you are standing way
back when throw the juice the coil. I have seen projects like
this one break out with four foot arcs the first time the switch
was thrown. You you aren't expecting it, it can be rather
surprising. I hope you took lots of pictures of the system under
construction.

Richard Quick


... If all else fails... Throw another megavolt across it!
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