Oooo, tripple post . I worked out the central bronze bearing and thrust bearings come to about $21 (with a spare centre bearing just in case). These are the thrust bearings:



The centre bronze bearing is a plain bore unlubricated type, which is very cheap and can be a disposable item. We can drill an oiling hole in it or go for a fancier grooved bearing like this:



These ones cost around $20 each, rather than $4.80 for the plain ones and I don't think they are really that much better.

Let me know what the dimensions of the steel bar / disk will be and what motor you are thinking of using. The next important things to design are the drive pulley to motor shaft coupling and the type of belt to use. I am personally favouring timing belts or multi groove flat belts like Jake uses as they are more energy efficient.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion