I did a post on mtbr about getting advice on these types of seat stays with the word “fastback” in the title and a builder deftly pointed out that there’s nothing *fast* about this type of seat stay joining method. Fastbacks are the traditional method of joining the upper seat stays to the seat tube at the back of the seat tube by either TIG or fillet brazing them on. But if you are not going to bend the stays and want a fatter tire on the back, you need to mount the stays to the side of the seat tube to give the tire more space. Lots of cool classic ways to do this for cross, randonneur, and mtb frames but I have my c.2000 Indy Fab Planet X cross frame lying around so I wanted to copy their method for my own learning experience. Turns out, harder than it looked. But I’m really happy at how it turned out. Most builders seem to use silver to braze on side-mounted seat stays since you don’t need to fill a big gap and you don’t have to heat up the tubes as much (which is important if you’re using scalloped tip seat stays (or like these). Seems like a tiny fillet of silver on these bikes but I guess it’s strong enough. I used brass and probably (likely) practiced overkill but better to be safe than sorry. Just means I had to file more brass off to make it look better before painting.
The caps I brazed on with gravity in the vise, then ground down before setting the frame up in the frame jig for tacking. The stays rest against the HJ65 SS bar and I hold them against the seat tube with a toestrap. I filed little divots in the seat tube so that there would be as little creep while brazing as possible. Not sure it worked for me but in theory it’s a good practice. I tacked with brass both at the dropout and seat tube before taking the frame out of the jig and into the bike stand for easy rotation and final brazing. The crazy thing is how LITTLE I had to ream the seat tube after brazing…it didn’t distort it almost at all. I had my crappy homemade heat sink in there but (my) TIG welding definitely distorts the tube more. Just thought that was interesting. I’m sure that doesn’t happen to more experienced welders with better heat control.
Anyways, frame #8 and matching fork is done and headed to my ‘test dummy’ Hayride just in time for the *end* of cyclocross season and 2 feet of snow on the ground.