To cadmium or not to cadmium...
 

So, I'm building my first frame with the help of a local builder, and last night we brazed the main triangle. The builder told me that he normally uses 45% silver brazing material with cadmium, because it flows better. Of course, it's also toxic. He said that since it's expensive stuff, he wanted me to provide my own brazing material (he's only charging me $15/hr for lessons), so I went to Airgas and all they had was Harris 45% safety silver without cadmium, so I bought a 3 oz spool of 1/16" wire.

He hadn't used safety silver, so we used it on the first braze when we were tacking the frame in the jig. He had the torch, and was having a very difficult time to get it to flow....to the point where we reverted to silver with cadmium to get the rest of the main triangle brazed. He theorized that perhaps cadmium needed lower tolerances between the tube and lug in order to flow.

Anyway, is there some sort of trick with safety-silver that you need to do in order to get it to flow? Do I need more space between lug and tube in order to get a proper joint? I'd rather not use the toxic stuff, but the silver with cadmium really was pretty easy to work with...

Thanks,

Pete

Don't use cadmium unless you can wear a respirator while brazing.

What kind of flux did you use with the Safety-Silv?

I've used both and I really didn't see any difference. Generally people don't use 45 with lugs.

Hmm. The flux was brown, and it turned clear at almost the exact same temp as the melting point for the silver.

Unterhausen, what do people generally use with lugs then?

56% for lugs. Cad free.

OK, thanks. Is this 45% cad free usable for things like dropouts, braze-ons, and seat clusters?

I basically think you can use 45% for everything. It is probably best used for something fillet or weld ike, surface deposition that holds adjascent surfaces together. You can use it for lugs, slip fits, but you need to pretend you are using brass, meaning high heat, then it flows fine. The problem with that is that the reason people prefer silver is the low heat. Manytubbings can take the high heat fine, for instance if the stuff you are working with could take TIG welding then it should be fine. Not that 45% silver will be as hot as even brass, let alone welding, just saying you can use that as a guideline.

You should probably use the safety silve flux as well. It is white and works nicely with the SS wire.

45% with Cad flows like 56% without. 45% without is thicker and doesn't flow into tight gaps like the thinner material.

Regarding Cad and health, I don't think the metal vaporizes into the air unless you cook the $hit out of it. There was some threads on framebuilders and this was the word anyway. When you grind off the excess filler you don't want to breath the dust but overall the health risks are not a deal breaker for those with some basic understanding.

Cadmium melts at 320C, so at any temp above that it'll oxidise and mix in with the other fumes. If you're breathing without a respirator you're going to end up inhaling some of those fumes. One-time exposure may not hurt you much, but it's pretty easy to avoid the risk, and I think it's just good practice to use a respirator (and/or fume extraction if you're in an actual shop) when doing any welding or brazing operation... same with grinding and filing your cadmium joints too. The dust is just as bad for you. A disposable respirator is a small fraction of the cost of all the supplies used in building a frame, and I think it's well worth it since you're likely to be at the welding store to get flux and rods anyway.

Thanks. I'll switch to 56%, and keep the 45% for doing fillets.