Re: big secondary coil

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

Original poster: "robert heidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-desertgate-dot-com>

Greg: I buy white PVC pipe from 1" thick down to 1/4" thick and from 5/8" to
42" dia so playing with sono tube seams a waste of time, but if you must
pull a tight layer of sheet polyethylene over it before you plastic coat so
the fiberglass wont stick. Phone your local irrigation supplier first.
   Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Fri, 13 Sep 2002 08:21:11 -0600
> To: tesla-at-pupman-dot-com
> Subject: Re: big secondary coil
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Fri, 13 Sep 2002 08:35:33 -0600
> 
> 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
> 
> 
>