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Rotating spark-gap materials?


Hello all!

I'm constructing a rotating spark-gap for my new magnifier set-up and the
material for the disk is quite an interesting question. Some people have
used a composite material (glassfiber+epoxy) G10 with success but at a
local price of 400usd for a 50cm*50cm piece of 10mm thick plate I find it 
much too expensive. I've looked for alternatives and found some - like
cotton-laminated bacelite (phenylic resin) at 100usd for the piece of
50cm*50cm and 16mm thickness. (prices converted : 4.8 FIM = 1 USD)

The question is which mechanical parameters are those to look for in the
material - tensile strenght, bulk modulus, ?? and how to calculate the
minimum values needed. I'm not a mechanical engineer so I don't have the
experience about this. Anybody on the list with knowhow on this one? 
I'd pretty much guess that thick bacelite disk would do fine..

My system as planned:
disk diameter 45cm, 24 electrodes at a radius of 20cm from the centre,
3000RPM. This gives about 1200 breaks per second. 

btw: I have constructed a very heavy (4" thick) wooden frame with
glassfiber&polyester coating for this gap and shall use an old washing
machine AC-motor for rotating the disk via pulleys. Electrodes shall be 
stainless steel acorn-nuts, connected in series eventually.

Thanks for any ideas!

Kristian Ukkonen.