I’m building my first fillet-brazed frame, and I’m ready to attach the seat stays. I want to do a traditional-style joint at the seat tube, where the stay ends are cut at a diagonal, capped with a bit of curved tube, and joined to the tangent-point of the side of the seat tube.
When I took my UBI class, we did this joint using silver filler, but that was for a lugged frame. With my fillet brazed frame, the seat stay will overlap the SS/TT fillet. So I’m wondering whether it’s a bad idea to try to silver over that brass fillet? Is there a recommended way to do this?
No problem, silver brazing seatstays onto a brass fillet is perfectly acceptable. I like to file in a divot in the side of the seat tube* and into the fillet for the stay to nestle into, increasing the surface area in contact. The contact area is nearly zero, a mathematical point, unless you make this divot.
**well, not really into the tube itself since I’ll almost always use some sort of demi-lug or reinforcing sleeve over the seat tube. Unless its an externally-butted ST or for whatever reason extra thick-wall there. Don’t go filing a divot into 0.6 mm wall tube.
Thanks! I had it in my head that silver wouldn’t stick to brass (or vice versa) for some reason. When I took my lugged class, we also filed a slight groove to promote a better joint.
I’m using an external-butted seat tube on my current frame, and also plan to make a very slight groove there also.
‘very slight groove’
Bear in mind that the material lost in making a groove is replaced with the steel of the stay. Also a bigger silver surface contact between the steel surfaces and longer fillet around the longer joint margin.
A good depth of groove, and the associated larger small-gap contact area, is probably less of a structural risk than just touching the tubes together and relying on a silver fillet to take all of the shear load.
I use straight gauge 4130 for sleeves. Start with .058 walled tubing that is 1/8" bigger than your ST diameter. I turn it down to about .040" wall thickness so it looks proportional.
I part off about 4 inches of the tubing, add my binder using a tubing block and sprung, grooved finger (pictured elsewhere here I think). That ensures the binder is square.
I then use the binder to index on the flat surface to mark center lines. This helps center the carving relative to the binder. Once the sleeve is brazed on, I use the binder to index from to make sure the bottle holes and miters are in the right orientation. My first few had binders that were off center or bottle holes that are off center. No one else notices but it drives me crazy.
