Originally Posted by KC8QVO

For what it is worth, I want to use something like a 3/8" diameter shaft - not much bigger. It isn't a heavy/high force transmission - in fact I am starting to think the bike chain and sprocket to hang on what I am wanting to attach it to is going to be too heavy for it. Though, if I jack shaft it with 2 gear ratios then I loose power in the jack shaft conversion. Going to a jack shaft, though, I could add a 1:2 ratio pretty easy. Then I would have a lot smaller input ratio than 1:7 in one shot (exact ratio doesn't matter much, I just need to get the RPM way up on something - on the order of 13,000-20,000 rpm, tested at around 16,000 and have room either end - preferably up).