Thought I'd share this as I've seen a couple of folks discussing/asking about the possibility of making a fixie belt-driven bike.
The answer is yes! It took a bit of time, money, patience, and ALOT of research. In the end, I'm pretty happy with how it turned out.
A quick bit of background... I recently got a new bike so I was retiring my old Kilo TT daily commuter. I have no metal working experience (and it shows) and somewhat limited bike assembly experience (I perform maintenance on my bikes and some minor upgrades) so I spent a lot of time researching how to do some pretty basic things (like how to remove a BB). Luckily I didn't make any major mistakes or have to redo anything. And before you ask, I'm not going to get into nor explain why I wanted a fixed gear belt driven bike... it tends to be a polarizing topic (especially on this forum) so if you're interested, please read on.
As all of you know, the belt in a belt drive system cannot come apart or "break" like a chain, so in or order to slip the belt inside the rear triangle, the frame itself has to "break". After some research, I decided on a coupler made by Paragon Machine Works. The coupler came in the diameter I needed for the seat stay.
With coupler in hand I proceeded to cut the seat stay (right one). I measured from the outside edge of the coupler (the exposed parts that do not slot into the seat stay) and cut a section of the tube a hair shorter so that I can file it down to the exact measurement later. Since the coupler has about 1/4 inch of a smaller diameter section that sits inside the seat stay tube, I knew I had to bend the seat stay at the cut-out to actually fit the coupler in. Given that the Kilo is steel this wasn't much of an issue.
Next comes the joining the coupler to the frame. After learning the difference between brazing and welding and the equipment necessary for it, I decided to braze the coupler onto the seat stay. At first I tried a propane torch but the flame was not hot enough to melt the bronze filler rod I wanted to use, so I bought some MAPP gas and that did the trick. After filling the gaps (and letting the molten metal do it's capillary action work), I was left with this:
At first I was quite worried at how ugly the joins were with the excess filler material bubbling up like that. I took an angle grinder and hand-file and very very very slowly ground away the excess material. Resulting in this:
I then finished off the joins by using a steel brush mounted on a hand-drill, which resulted in the final joint:
After painting and assembling the various new parts I bought, here are some pics of the finished product:
The rear cog:
The front "chainring": Note about this, I initially bought an installed a 55 tooth chainring (belt teeth count the same as chain teeth) but later upped it to a 60 tooth. The smallest rear cog that Gates makes is the 21 tooth fixed gear cog, due to the belt not being able to bend as much as a chain without affecting the strength of the belt. Since this was going to be my rain/icy roads bike, I wanted a lower ratio than what I normally ride but didn't want the ratio so low as to affect my top-line speed. The 55 tooth left me spinning like a crazy person even on flat roads; the 60 tooth feels just right.
Hope you enjoyed reading my post. If you're interested in doing this yourself and have any questions, please feel free to ask! While I'm no expert at any of this stuff, I'm happy to give it a try.
Oh I do want to caveat that this is potentially dangerous if the brazing is not done properly.
While I have no idea if I myself did it properly, I'm willing to accept that risk and I stress-tested the finished bike by abusively hitting every pothole I can find and going up and down curbs and then inspecting the bike for damage. I've ridden this bike for about 2 months now with no issues.