Brass or copper spheres

[TinselKoala]

Telluric, if you are making your machine as a HV source for real research and not just for looks and nostalgia, a Bonetti machine will be far better and much easier to build than a classic Wimshurst. The Bonetti machine is nearly identical to the Wimshurst but uses plastic discs with NO metallic sectors. It turns out that the sectors actually decrease the available voltage and current by providing many edges where field strength is high and corona blows away charge.
The sectorless Bonetti machine stores charge on the surfaces of the dielectric disks and can reach much higher voltages and currents than the standard Wimshurst machine.
http://www.youtube.com/watch?v=yYGFqkXjwZc
http://www.youtube.com/watch?v=ir9RIsXzmzY

[telluric42]

thanks all this is all good stuff  .....i agree with you TinselKoala the sector-less machine will give me more grunt i will consider building both as i do like the look with sectors. interesting how it always comes down to sharp edges (losses).

cheers