I wish Sheldon Brown were still around to ask, as I recall reading that he had done such.
I'd like to be able to run three rear sprockets on on my Shimano 8speed hub.
I know I could run a triple on the front, but:
1-Rear derailleures work WAY better than front ones.
2-I'd still need a tensioner in back which is most of the weight and pain of rear derailleur.
3-Much easier to guard the chain/chainwheels with no FD.
4-Less weight in small rear sprockets vs. big chainwheels, and FD+tensioner vs. RD
Sheldon mentioned brazing I think (I can't find the article where he mentioned this.) It looks like the way the Shimano sprockets are dished/stamped I'd be asking for lots of warping if I got near them with a torch. I could probably press them back into truth, but maybe there is a better way?
I have machine tools and all welding processes available. I can do this, just wondering if anyone can save me some pain in learning what works.