I have a lathe and milling machine and would like to make my own parts for servo motors horns, wheels, or take up spools. But how does one go about machining that serrated interior hole? Is there some sort of broach I can get for it?
If one couldn't buy an appropriate broach, one would presumably turn, mill, and harden some tool steel and make his own. Depending on the quantity, HSS will be just fine for aluminium. An arbor press and a simple jig will take care of the rest. A machinist's vise can substitute for the press.
It would be far simpler to just buy some anodized arms and modify them. Me personally, I would probably file a flat on the splines and run a setscrew up on it. Plenty of room to get fancy elsewhere.