so about that black flux...

don't believe everything you hear about it. it's way better than white (for me to learn with at least), but it's not a complete cure-all. witness the following bits.

the BB shell is the Long Shen i filed but couldn't use due to chainstay fit problems discussed in earlier posts. the head lug is a $2 Rivendell reject. i did the shell Sunday and the lug earlier today. on the lug i tried all the silver i have now: Sif 55%, Wolverine 45%, and Harris 56%. the higher-Ag pair felt about the same...maybe the Harris was a little faster to flow, hard to say.

first, BB shells are frickin'hard. there's pins in the way, there's a lot of surface to cover, and the thing is thick. i thought a bigger tip would help with the extra bulk. i tried a #15 in my PurOx/OxWeld rig, compared to the #6 i used for the previous sleeve joint. (the only intermediary step is a #9.) this was so big that i couldn't direct heat where i wanted it when doing more focused heating of the area to be brazed. broad convex surfaces worked fine, though.
also, i find my brazing improves dramatically over the course of a joint. when i start, i tend to overheat things badly, but after a few minutes it's like muscle memory kicks in a little and i'm better. so there's a few spots that are nicely done, and those are the last spots i did. i think before i do any "real" frame brazing, i'll warm up on mild steel.
the damn curly things on the Riv lugs are really tough, they're so small and right at the edge. i burned the hell out of one.
for the head lug i had the shop to myself so i and set up 2 torch rigs. i set a #9 for preheating and a #6 for brazing. i had tried to change tips mid-braze before, but that took so long that it almost wasn't worth preheating with a larger tip. the 2-torch way worked well enough that i'll likely use it again, maybe with a #9 and #4 instead.

it's pretty much a perfect Z shape.

here i it got way too hot and i could tell i'd done it.

this i like. i broke off the pin and filed fluch to try that part out.

no silver penetration around the DT at the BB shell √° la Little Fish's first Audax. i'm glad i tried a BB beforehand.

1 comment:

Anonymous said...

"i find my brazing improves dramatically over the course of a joint"

Pun intended?

-Chauncey Matthews