Cheers BB.
Some "how d'yja do that" notes.
The ally bearing holders were cut from a piece of 1/2" thick ally plate with a wood working table saw and the neat fit holes for the bearings were drilled with a wood working forstner bit with metho lube. It probably doesn't need ball bearings for intermittent use, just plastic bearings would probably be OK.
The rim sprocket bush with the spline was turned on a metal work lathe and the keyway was cut with an dremel with a thin cutting wheel and tidied up with a needle file but I don't think it needs to be that fancy. Given the back pressure provided by a wire brush is not high a simple firm fitting bush (ie no spline) bolted in position and the rim sprocket help in place by firm oversized washers would also work just as well.
If I was making it again I would make the spline over length like a chainsaw, so the rim sprocket could float into position in line with the bar. On my system the bar is allowed to hang by the chain and find its own sideways position and bar nuts are the turned into position behind the bar so the bar stays aligned.
At low speeds the chain will run without a bar but at higher drill speeds a free wheeling chain can tangle up on itself quite badly and also whip around and hit you (I tried all these things
)
The setup also doesn't need bar nuts, but it does need bar bolts. Without the bar bolts, (ie a free hanging bar/chain) the chain may jump the bar (especially if bar and chain are dirty) and the bar will fall out - if a soft receptacle is arranged for the bar to fall into (I used a polystyrene box) and a slow chain speed is used this may be acceptable to you. However, if the drill is too fast, which also contributes to why the bar falls out) when the bar falls out is also when the chain usually tangles and whips around and hits you - I also tried this.
At a minimum I'd recommend bar bolts or something else that prevents the bar from twisting and then fall out of the chain cradle.
Bar nuts allow you to go full speed with the drill safely which I think is also probably better for the drill.
BTW this was all done with a cordless drill at 500 rpm or less. I would not use a corded drill that can go above these RPMs. I've tried it with my setup - its dead scary!