Heya fine peoples.
So ive been mulling over this question ever since i completed my last frame.
For a few reasons, i chose to use a external sleeve on the seat tube for the clamp and top tube junction.
Mainly cos it gave me the appropriate sized tube for a clean fir with the max top tube.
But i had a shit time brazing the sleave. This is more than likely my terrible brazing
But my question is, in what order would you do this ? I welded put the entire frame, then brazed the sleave and clamp boss on.
But ive been mulling over, and i THINK it would be better to braze the sleave (stainless tube silver brazed to the max seat tube ) prior to frame assembky much the same as i did for the bottle cage boss etc etc.
My thought being, the seat tube will have a proper heat sink during weld out, the sleave is relatively substantial (2.4mm tube from memory ) so, along with the heat sink… i cant see enough heat getting into the braze to re melt it ?
Thoughts ? Am i over thinking it ? Am i missing something blindingly obvious ?
Yeah, do the sleeve first and extend it down another 5mm below where it is now. Ensure that the silver at the edge stays solid and retains the melted silver from welding under the sleeve
The sleeve doesn’t need to be fully brazed anyway. Just flow a little silver in the bottom to hold it in place and make it look nice under paint and then build the rest of the bike.
I’d always leave the brazing for the end. It’s likely ok to weld over your silver brazed collar but I never did just in case of contamination from beneath. I’d just use a magnet or paragon tube block to keep it in place while mitering the other tubes. Then I’d weld it all up and lastly braze it with silver stuffing as much flux in there as possible. That way you can also do all the cable guides and other stuff at the same time and only soak and clean once.
I think that was my thought process this time
But with a fairly chunky sleave, the chances of a full pen weld off the 0.8 top tube bringing somthing through would have to be fairly low right ?
Thanks to all for the responses
Mark Bulgier talked me into making a stepped extension instead of a sleeve. It’s easier to braze (because you aren’t pulling silver for many cm) and the brazed joint is far away from your seatstays and top tube joint. It’s easy to make on a lathe.
Like this, hopefully minus that shallow score mark:
The shelf part of the way up is about 0.9mm to match the seat tube. The tube started as 31.8 x 0.095, which is just about right for a 27.2 seatpost.