I was unaware that anyone had considered this low buck concept (kinda disappointed, but not surprised). I did some basic math on the speeds encountered by a brake drum at operating speed of 5,000 rpm engine speed @1:1.2 overdrive with 3.73 gears and got 1600 rpm. About half the speed the motor turns.
But my idea is to have the motor shaft slip into a drilled hole in the flange, and the drum to bolt up to it backwards (facing upward away from the axle stub). The motor bearings would support the load. The weight of the drum should be relatively irrelevant, and the idea is to balance it so it shouldn't vibrate, but I suppose the higher speed of the 3550 rpm motor might theoretically spin the drum apart. I'm gonna guess turning at twice the speed shouldn't spin the iron apart, but inside a stainless steel cookpot (the spun oil catcher) if it did spin apart, I don't think it could getcha.
I will post pics when I give this a try and give a full evaluation if it is successful, but I am still waiting for the motor and need to take a trip to the junkyard for the drum. The donor axle is one I broke 'wheeling.
But if it DOES work out, this will be a VERY cheap build. It will require a fair amount of machining on the drum, and some relatively minor drilling/tapping. My hope is that this project may make a centrifuge financially attainable for anyone. Even if you have to pay for the machinework, it should be a LOT cheaper than the billet aluminum ones.