... after thinking again about Electrum's big rotary, of course there must
be 4 discs! Because they are full-metal discs made of aluminium, only 2 gaps
per disc are possible.
The use of full-metal discs at this power levels is the best way to avoid
thermal problems and also this gives you the highest mechanical strength. On
the other hand, the use of an insulating, phenolic shaft is the big
challenge on such a design :-)