Phil Williamson wrote:

 Can one use the 12a parts to build a three rotor? I'll have extra parts left
over from these junkyard 12a's. I'd love to go for a three rotor.:-)

 Phil

Do you have a big lathe Phil? The shaft is custom for a 12A.
You need to machine it out of 4340 oversize. Have it heat treated.
Grind and polish it to final size. Maybe have it nitrided and then 
final ground. Not cheap. Unless you are set up for it. 

You might as well go for 13B housings and rotors.
 
Paul Lamar
 
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