Re: big secondary coil

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

Original poster: "Greg Leyh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <lod-at-pacbell-dot-net>


>Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net>
>
>Casting about for ideas on inexpensive, but high performance, forms for a
>secondary around 18" (50 cm) in diameter and 6 ft (2 m) long...
>[snip]
>But, what about taking the sonotube, putting 1 or 2 layers of
>fiberglass/resin composite over it (or, you don't even need glass, you
>could just use canvas as the fiber).. wait for it to cure (at least to the
>"tacky" stage).
>
>Wind your coil.  Fix the windings with something (another layer of glass?..
>urethane? glyptal?, etc)...
>
>Remove the sonotube by scoring and water soaking it.
>
>I think Greg Leyh did something like this for Electrum....

Pretty much.  The sonotube was first wrapped with 3mil
poly however, to provide a mold release.  The sonotube
was mounted over a 22' steel arbor, as the paper tube
by itself was not rigid enough.  A winding jig supported
the steel arbor on both ends and rotated the tube for
placing the wire using a 2HP gearmotor.  After fully
wound, the coilform received a 1" thick fiberglass layup
using a chopper gun.
After the glass kicked, a router cut two fixed depth
grooves down the inside of the sonotube, and a pressure
washer removed most of the sonotube from the inside.
The mess in the parking lot was substantial.


>Questions:
>
>How much fiberglass on the inside?  The windings themselves will provide a
>fair amount of strength. For more longitudinal strength, one could put some
>sort of insulating beams on the inside (fiberglass tubing or PVC pipe)
>
>How would one make a mounting fixture for the secondary?  You could "glass"
>in a piece of 3/4" plywood in the bottom.  Ideally, one would want to be
>able to support the secondary horizontally as a cantilever attached only at
>the base (sort of a worst case...)

Electrum has 1" thick walls in order to support the
stresses of wind loading up to 150mph.  Lateral struts
inside the secondary were not possible as they would
obstruct the central manway.
Each end of the coilform has a thickened edge, and
the base end has four steel weldments laid up into
the fiberglass build.  The weldments support the
coil tower and anchor it to the concrete vault.


-GL