This may be superficial, but, using aluminum in DIY blocks usually, is asking for trouble. Aluminum doesnt mix well with many other metals such as copper, especially when it isnt anodized. Sure, there are ways of preventing the degredation resulting from electrolysis...
If you are making a rotor, don't go out of the way to make it aluminum.
Drilling copper is pretty easy too, granted you keep the drill bit cool and lubricated.
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