PrairieDog

Hi everyone, this is my first time building with both brazing and building a frame. I got a little instruction on brazing from a colleague who is a metal sculptor, and have been working from instructions from Marc-Andre Chimonas' book. So far I have the main triangle and chain stays brazed together. I'm using Columbus cro-moly and lugs, with 56% silver.

Here is where I could use some advice: In brazing the chain stays to the bottom bracket, I used too much silver and some of it pooled as lumps in the bottom bracket. It isn't a lot, but it is enough that it messes up the threads.

How should I deal with this? Should I grind it out? (Doing so would still leave me with plenty of threaded bottom bracket.) Or should I re-flux everything, apply some heat and try to draw it back down through the lugs to the outside? Or is there another way of dealing with it?

Thanks for your help with this. However it turns out, I'm having a blast.

Oh, and here is my blog, where I'm posting about the frame build:
https://www.thebikegarden.com/

mudboy

Grind out the excess without hitting the threads, and then chase the BB shell with the appropriate taps.

PrairieDog

Thanks, that what I was thinking, but I wanted to be sure that it was the best way to go.

JohnDThompson 

I use a solder wick to pull out brazing material from lug sockets when repairing frames:

unterhausen

warning, Pete, feel free to avert your eyes

you can heat it back up and knock the excess loose with a welding rod. You really don't have to get the bb shell all the way hot to do this.

PrairieDog

OK, a couple of questions: how does a soldering wick work, and what is a welding rod? (That is, by "welding rod," do you mean the same 56% silver rod I've been using, or something else?)

unterhausen

no, by welding rod I meant something that wouldn't melt, like steel welding rod. Now that I have had time to think about it, I have done this once, and I used steel wire rope. I was thinking I might be able to wick the silver onto the wire rope, but it worked as a brush and I couldn't get it to flow out onto the wire.

mudboy

Solder wick looks exactly like the old Shimano braided mountain bike brake cables.

PrairieDog

OK, thanks, everyone. That gives me some options to think about. I'll pick one and give it a go this weekend to see what happens.

JohnDThompson 

The solder wick is just a section of braided steel cable. You heat it up and stick it into the puddle of brazing material. Capillary action pulls the material up onto the wick. You can then remove the wick and optionally give it a whack on a hard surface to eject the material and pull up more.

PrairieDog

OK, here's an update on what I did and how it turned out. I liked the idea of the wick, but when I went down to my local welding supply place, asking for a solder wick produced some head scratching. It was probably silly of me, but I also tried some old brake cable on a practice spot and found that it wasn't going to work as a wick. Though they didn't take up a huge area in the bottom bracket, the spots of excess silver were pretty large and I wasn't keen on grinding them, though it probably wouldn't have mattered in the long run as far as function is concerned. So I thought I'd use the "heat up and knock it loose" method suggested by unterhausen. If it didn't work, I could always grind...

I fluxed everything well, put the torch to it, and before I could get the the "knock it loose" stage, the excess simply drained through the threads and down into the chain stays. There is one little lump left, but it should be easy to grind away. Everything else is pretty clean, and it looks like the threads will be easy to clean up with a tap.

I may be going about this frame building thing all wrong, but by golly, I'm having a good time and the frame itself looks halfway decent. It may even function as a living, breathing bicycle someday.

Thanks for your suggestions, everyone!

unterhausen

I was going to mention this before, but since you got excess penetration into the BB, you are miles ahead of most people on their first frames.

PrairieDog

Thanks for the words of encouragement, unterhausen. Before I started the project, I saw a photo of a broken BB on a blog about framebuilding that was the result of not enough filler penetration. That made a big impression on me, and so I think I am erring on the side of too much filler on all my lugs. I wound up re-doing each at least once before I got brazes with plenty of filler and without any gaps. As a result they all have excess filler around the perimeter and my seat stay fillet brazes are ridiculously robust. It is making for a lot of filing and clean up, but I figure as I get more experienced, I'll develop more of a feel for the right amount. In the meantime, seeing the extra filler come out the other side helps me feel confident about the integrity of the joints.

unterhausen

with lugs and silver, many experienced framebuilders flow the filler starting from a safe area that will be cut off later. Examples are extra head tube or seat tube sticking beyond the lug. If there is excess, you can just flow it back and away from the lug. There is nothing I hate more than cleaning up excess at the shoreline. Obviously, you can't really do this for a bb shell.

PrairieDog

Yes, I've been finding that cleaning up the shoreline has been an interesting challenge. I'm using a lot of different files and rifflers, but even so, it's a tedious process. That's good advice about aiming the excess filler for areas that can be cut off later.

cycle_maven

One of the tricks I use to keep silver off things I don't want it to flow onto in my jewelry work is to paint the area with White-Out (not the water-based kind, the volatile type). The silver won't stick, and it cleans up easily afterward- just turns to white dust upon heating.