Garolite (G9, G10, G11) questions.

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Original poster: "Sam Barros by way of Terry Fritz <twftesla-at-qwest-dot-net>" <list-at-powerlabs-dot-org>

 Greetings,

 This question concerns materials choice for a rotary spark gap. 
Obviously we want the rotor disk to be as light as possible so that 
a smaller motor can be utilized and the spin up time becomes shorter.
In order for a light disk to withstand the centrifugal forces encountered 
in rotary spark gap duty it would make sense to use the strongest 
material possible (within some price restrictions obviously). I notice 
that G-10 grade Garolite seems to be the most often used material,
and with a tensile strenght of 40000PSI and an impact strenght of 
7ft/lbs/in it is definitely a good choice. I also see some designs 
using polycarbonate but at 9000PSI tensile strenght, 12ft/lbs/in 
impact strenght I would definitely go for G-10.
 However, why doesn't anyone use grade G-9 Garolite? With a tensile 
strength of 66,700PSI lenghtwise and 51,900PSI crosswise, and an 
impact strength of 14.5ft/lbs lenghtwise and 11,2 crosswise, it would 
make a much better material choice for a lighter, stronger rotary 
spark gap disk, no? The price is also virtually the same as G-10 
($29 for a 1/4in thick, 1'x1' sheet). Also, what about other grades 
of Garolite (G-11, G-30)? They seem to be weaker and more expensive,
is there any advantage to them? Is there any plastic/composite material 
that is NON CONDUCTIVE and stronger than G-9?
 Finally, how stiff is G-9? Does it buckle under force or does it 
tend to fracture in a brittle fashion (I am deducing from the relatively 
low impact strength that it will shatter, but I couldn't find its 
modulus of elasticity anywhere)?
 Any answers to these questions would be greatly appreciated.

Sam Barros
ME/EE Major at Michigan Tech.
http://www.powerlabs-dot-org/