dabac

Hi,
I'm looking to repair a frame where the DS chainstay has come apart from the dropout. It's meant to be brazed but there seems to be precious little brazing material in there.
Now, I'm undoubtedly better at welding than brazing, so I'm thinking of simply finishing clean-up, slotting the DO back in and weld the rounded ends to the DO.
Apart from aesthetics, any reason not to do that?

JohnDThompson 

No, it shouldn't be a problem, provided you take care to completely clean both the dropout tab and the inside of the stay. To avoid a repeat of this problem, sink plenty of brass into the stay. Lay a bead along the margin of the domed stay end, then use the torch to draw the molten brass into the stay. Repeat until you've filled the stay end (you can tell by how quickly the stay cools after you remove the flame; if it cools quickly, there's air under that part. If it stays glowing, there's brass).

Andrew R Stewart 

I believe the OP was talking about welding in the US terms. While John and I seem to prefer to brass "weld' (to use the Brit term) I will try to answer the OP's question.


The big question I have is the integrity of the last bit of the stay, the domed end. I have seen these crack at the base of the slot, where the dome becomes the size of the stay diameter. This is why I was taught to fill the stay's end well into the drop out/stay overlap, past the slot, when brazing. This ensures the stay's complete diameter also captures the drop out tab.


The other concern, which I have no personal experience but have read of problems with, is the potential to not completely clean off the previous brass before welding. IIRC welding doesn't like brass to be present in the joint.


What I would do is pull the drop out tab fro the stay. Do as much clean up as I could and brass the tab back in place. But this is what I know best, and the best repair is what the guy can do best. Andy

dabac

Hi all,

Apologies for being unclear. With welding I mean arc welding. Wire-feed MAG.

Don't think the small torch I have easily at hand will get the DO warm enough for brass brazing.
And I have some concerns about not getting the inside of the chainstay clean enough for the brass to wet properly.
I've pulled the joint apart. Can get the actual slot clean enough, But not the inside of the tube.
Am aware of the dangers of trying to weld on top of brazing, But there's not a visible trace of brass at the seam.

unterhausen

Since it is two rather different section thicknesses, I suspect it's not going to weld the way you want. And any residual bronze is going to contaminate your weld. I don't know what kind of torch you have, but it doesn't really take that much to braze a dropout. I agree it's going to be difficult to clean inside the chainstay. I'm not sure if you can chemically clean it in such a way that bronze will stick. And those domed stays weren't easy to braze, this is a fairly common failure.

JohnDThompson 

That, and the previous issue you mentioned about the tab breaking at that place together argue against welding as a fix.

A fuel/air torch may not be able to get the work hot enough for a reliable brazed joint. Fuel/oxygen of any sort ought to suffice, though. You could cut the domes off and clean the inside with a round file, then fill the opening with brass. Some creative positioning for gravity assist may even allow a new dome to be built up in brass to match the other side, if that's important.

Andrew R Stewart 

John's suggestion to cutting off the dome to be able to best clean the stay ID is equally valid for brazing or welding. If you're going to frame repair a proper torch and brass work is invaluable. Andy

Brian25

I suggest making sure that you line it up as best as possible and tacking it back together first, never assume tat it is properly lined up, you really need to quality control that the wheel sits properly in the rear end (not to the left or right of the chain or seat stays). Assuming it passes Q.C. Then weld (whatever means you finalize on) the crap out of it.

CliffordK

What material is it made out of?

One of the reasons for brazing was that older materials (Reynolds 531) were supposed to not tolerate the heat of welding well.

fietsbob

brazing would require clean surfaces so you would have to remove the seat stay joint to clean up

the chain stay joint..

TIG is the industry favorite these days, still need clean metal for a good weld.