By James Morikawa
6 January 2007
On this frame, I plan to seal the tubes and stays, and fill them with argon gas. The exception will be the seat-tube, and head-tube, which can't be sealed. To check the welds and brazes for possible leakage, I pressure test the tubes. Tubes have to be leak-free for the purpose of sealing in the argon gas. I once thought of using helium, but due to economics, that never happened.
The purpose of sealing the tubes has been to prevent internal oxidation (rusting). I've thought many times, "has it been worth the extra labor to do it?", "Wouldn't it be easier to coat the internals with JP Weigle's Frame Saver?" "Sealing, is it all that necessary?" Well, I begin to feel, more and more, that's it's not all that necessary.
But, since I've been doing it . . . I'll attempt to document it.
There's a small hole drilled in each tube, except the seat and head tube.
These holes were used for internal argon-purging during welding and brazing. I have an argon-purge set-up that allows me to purge via these holes. Anyway, I'll be using these for pressure testing.
I hope the pictures below give you an idea of what I'm writing about.
Above, are the top-tube, and down-tube set up for pressure testing. I pressurize the tubes to about 100 PSI (compressed air). I then spray soapy water around the welds. If the soapy water bubbles, I have a leak and need to repair it. I once had a leak, that sadly, was a stress crack in the tube wall next to the weld, I ended up trashing that frame. I never would have noticed the tiny "crack" if I hadn't pressure tested.. Not a good idea to be heating, and reheating, and doing second pass-welds on some of those ultra thin steel tubes.
Anyway, on this frame those tubes were leak-free.
This was a depressing moment for me. It was a freaking bummers.
I was pressure-testing the right seat-stay, and then I see bubbles. I had a tiny leak. I know what caused this: I had forgotten to turn on the argon purge when I did this joint. I've found that using an argon purge during brazing extends the anti-oxidizing quality of the flux, and I can sweat in some really nice internal silver fillets. I remember forgetting to open the argon flow on this joint. A nice excuse . . . I still should have been able to get a tight sealing joint, but didn't. That was just "shitty brazing". On these "fast-back" mitered joints I like the miter-shoreline showing, and braze to do so. I won't be able to do that here because of the leak. Got to repair it.
I used Harris 50N silver braze to make repairs. I used Harris 45 when first brazing the joint which had the leak.
50N is sticky flowing stuff, which allows me to build it up. Anyway, flowed 50N silver around the joint, then filed, and sanded to a fillet looking joint. Rechecked for leaks, and all was OK. I usually don't encounter leaks, but on this frame I did . . . lots of room for improving.
On a couple of frames, I tried to tig-weld this joint . . . like master-welders Don Ferris, Carl Strong, and others I don't have names for. I found it a difficult welding task. Here, there seemed to be, no margin for welding errors, and I made too many. I ended up with darn ugly looking seat-stay welds, and eventual trashed the frames. If you can tig-weld this joint, and end up with good looking welds, you have my highest respect. I'll stick to silver-brazing them for now, but someday I should make another attempt with the tig-torch.
Goodnight.