Re: Copper plated toroids: is it practical?

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

Original poster: "Scott Hanson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <huil888-at-surfside-dot-net>

Although its simple to electrolytically apply a very thin layer of copper 
on small metal objects, its quite a different task to apply a heavy, 
uniform plating of copper to a large non-conductive object.

A bit of analysis of what you want to end up with vs what you can 
reasonably achieve may lead you to abandon the effort before you dump too 
much time and effort into the project. Since adhesive backed aluminum and 
copper foil tape is readily available, you might consider the cost, effort 
and performance of a plated toroid vs a taped toroid.

The first problem in a plated design is how to fabricate a relatively rigid 
substrate on which to apply the plating. Anything soft like styrofoam is 
probably out of the question because even if you could plate it, it would 
be so delicate that any normal handling would quickly dent or puncture the 
few-thousandths of an inch thick copper layer. A wooden toroidal form can 
be turned on a wood lathe, but to glue up several pieces of wood into a 
blank, fixture it and machine the required profile into both sides is not a 
trivial task, not to mention the finishing and sealing required to make it 
completely waterproof so it could be immersed in a water-based plating 
solution.

Assuming that you can fabricate a relatively rigid "form" to apply the 
plating to, how do you make it conductive? Some options are:
1. A metal film applied by vacuum metallization (usually not available to 
home experimenters);
2. A layer of conductive paint. Copper or nickel filled conductive paints 
are available for EMI and ESD shielding of plastic enclosures for 
computers, cell phones, test equipment, etc, but are fairly expensive and 
not readily available in small quantities. $25.00 for eight ounces of 
conductive paint from the "Caswell" hobby plating outfit sounds quite 
expensive to me, and 8 oz might only be enough to cover a very small toroid.

3. Burnished-on graphite powder. This was recommended in the past for 
making wax "replicas" plate-able, but it sounds very messy.

Assuming that you have finally fabricated a toroidal form and made the 
surface conductive enough to plate, how do you actually make electrical 
connection to the conductive coating and get the thing submerged in a 
plating bath? If the substrate is buoyant  (wood or Styrofoam), how will 
you get it covered with the plating solution? If you only partially 
submerge it, you will need some sort of motor drive to keep the form 
rotating into the plating bath.

Assuming that you have finally gotten a conductive form submerged in a 
plating bath, and made electrical connection to the form, how much plating 
is required to give a mechanically or electrically robust layer of copper? 
A layer .004" or .005" thick might be reasonable, so you will need to 
determine the total surface area of the form to know how much copper you 
need to make available in the plating bath. As far as the plating power 
supply goes, how much current is required for the surface area of your 
form, and how will you monitor and control it?  As the bath "plates-out" 
onto the form, you will also need to monitor the concentration of copper 
sulphate in the solution and replenish it as required.

As you can see, there are more than a few "issues" that need to be 
understood to get good results.

If you've not tried a "taped" toroid, go to Gary Lau's website and see his 
small (3" X 6") aluminum-taped toroid made from a blow-molded polyethylene 
pallet cushion 
(<http://www.laushaus-dot-com/tesla/minicoil.htm>http://www.laushaus-dot-com/tesla/minicoil.htm). 

I've made several toroids identical to these and had very good results on 
miniature coils (18" arcs out of a 2" X 11" secondary, powered by a 9/30 
NST).  See 
(http:///surfboard.surfside-dot-net/Huil888/Mini-Coil_w-toroid.jpg). This 
taping technique can be used to make much larger toroids. The aluminum tape 
is relatively inexpensive from Home Depot. The copper tape (3M is one 
supplier) is quite a bit more expensive, but gives a unique appearance.

Regards,
Scott Hanson