Why not write about it?
I stuck a wiki and a journal together because I'm complicated like that. The journal is for passing thoughts and observations, the wiki is for more sketched out ideas.
Sometimes you'll see a link to a wiki page that hasn't been written yet. Don't worry, it will be at some point.
The leather belts come long, you cut them to size and then punch a hole in the ends to insert a metal clip. Since there's no standard length I had to find something just as adjustable. I didn't have to look very far, as a drive belt is a pretty standard item.
At http://www.mcmaster.com (they have EVERYTHING for the mechanically inclined) I found urethane hollow-core belts that can be connected simply with a small metal connector. You cut the belt to length and then insert the connector in the ends. I thought that perhaps the connector wouldn't be enough to hold the belt together under load, but it works fine, even on my hard-to-treadle Serger Conversion. You can still pull the belt apart by hand if you need to adjust the length, it just takes a good strong pull.
As far as I can tell, unlike leather it doesn't stretch, so the belt won't have to be readjusted over time. It's also very 'grabby' and won't slip like a leather belt. The only thing is, it's bright yellow with black printing on it.
I used a 3/16" OD (outside diameter) belt and it fits perfectly in my Singer treadles.
Other things like waxed cotton or hemp cord should work as well (I'm guessing really), if you can join the ends properly.
Here are the part numbers from http://www.mcmaster.com:
6567K56 Urethane Hollow Core Round Belting 3/16" OD, 1-1/2" Minimum Pulley Diameter In stock Quantity Per Ft. 1-199 Ft. $0.68 200 or more 0.61
6567K26 Aluminum Connector for 3/16" Outside Diameter Urethane Hollow Core Round Belting