Non-electrical conductive machinable material

[onthebay]

Hi,

I'm searching for a machinable material that in electrically non-conductive and can withstand temps up to 400C. Preferably looking for round-stock > 3"-diameter. I've already looked into machinable ceramics but the cost is > $100 / In.

Some type of sheet might work too that I can cut. It will be approximately 3/8" thick when completed x 3"-dia. And will be sandwiched between a piece of 3"-diameter aluminum and several electrical leads.


Thanks

 

[MATLABdude]

You could try glass, some of them are machinable (or blowable / moldable if you have access to a glass blower, and/or can have some molds made). Outside of that, you might want to look into thermosetting plastics:
http://en.wikipedia.org/wiki/Thermosetting_plastic

Polyimide sounds like it might meet your temperature requirements. Unfortunately, things like teflon and PEEK are just inside (~340 C) of your desired operating temperature:
http://en.wikipedia.org/wiki/Plastic#Special-purpose_plastics

EDIT: Just noticed the other bit about sandwiching this stuff between electrodes. You may want to look into high-temperature silicone, as well. If you need really precise shapes, you can probably get something cast. I googled silicone sheet, and these guys popped up (they'll sell you silicone slabs of varying firmness, depending on how much deformation you can accept):
http://www.stockwell.com/pages/materials_silicone.php