Hand-filing about 60 teeth to a decent-looking profile must have been a hassle, Diablo, I don't think I'd have been prepared to do it, nor would I have ended up with all of the teeth seeming to fit pretty well. Congratulations.
I'll with-hold judgement on the viability of poured urethane gears - I don't think the Shore hardness gives a reliable indication of the stress and durability capabilities, though it is certainly a useful start. I hope you make one and report here on its performance, it would be a very interesting, and potentially very useful, project. I have never shared Deejay's dislike of the SB430 (I'm not so keen on the SB590, due to the lack of a second clutch) and it seems to me if the drum gear breakage problem, and the catcher availability problem, could be solved these would become quite interesting mowers.
