You could get the tapers done on a sink edm.

 

What would be the rough cost of something like that?

Keying/splining is quite cheap. Not sure what the advantage of a taper would be over the cheaper option.

Still, I'm about 50/50 on whether to make or buy the whole mess...

 

I think you should buy everything..., not to discourage you, but it would be less of a headache to buy someone elses proven parts.

 

Not sure on the cost, I'll get you a rough estimate as soon as I see the guy that does our sink edm.

B6T is probably right though. There's a lot of things I could make that I buy simply because the development has been done. Let someone else pay to figure out the right way. Don't get me wrong, it's cool to invent and create your own stuff. But a shaft could cost you $10,000+ by the time you work the bugs out. Build an engine, it breaks, build another one, find a new problem. I'm sure you've already thought about these things. Not to mention the time factor. (that's the biggest thing for me, I've never got any free time)

Like I said, I'm not trying to discourage anyone from trying new stuff. You've done some really neat stuff already and I'd like to keep seeing new and unique stuff. Either way, if you build one it'll be amazing. I've never seen one in person.