VTTC Variable Capacitor

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

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Folks

I got lucky this week and picked up for free 24 17" x 34"x1/4" thk
Lexan (polycarbonate) machine guard panels that were mis-cut and
were written off the plastic suppliers book...   :^))

Questions:
1.  What is the safe standoff rating of 0.25" thick Lexan to 60 hz
     modulated CW RF?  Most spec info I've found indicates ~250V/mil
     (62.5kV???  :^?  [doubtful] )
2.  What's the tan (phi) loss factor of PC versus PE or polstyrene?
3.  Does anyone out there have experience building a PC cap, if
     so how was it's performance?

I've got a design for a variable capacitor with PC insulation and a
stack
of two interleaved vanes with PC insulation between the two
moveable vanes, which rotate together in middle via an insulated push
rod operated by an eccentric on both shafts..

One rotating shaft is a pivot shaft, one shaft is driven via a
precision
vernier/bevel gear reduction drive.  With 15 panels cut in half,
allowing
30 dielectric plates, approximate capacitance (depending on final
plate
geometry and assuming dielectric k of ~2.2) was in 4500-6000pF range
fully engaged, in a capacitor with total footprint of 18" square by
about
10" thk.  Total rotation from min to max capacitance is 45 shaft
degrees.

Looks good on paper, will start building after the first of the
year...

Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA