krems81 

Any ideas for putting this back on? Braze? I have a basic Home Depot brazing kit. Any chance I can get it back on in a sturdy way without massive paint damage?

Wasn’t planning on refinishing this one

thinktubes 

JB Weld

jackbombay

That is what I would try, zero paint damage.

I would carefully use a file to remove the rust and even take the corner of the end of the file and giuge up both surfaces as much as I could to give the JB weld as much as possible to grab onto.

non-fixie 

I'm not familiar with JB Weld, but if it is some sort of super glue, then yes, that's what I would do. And like jackbombay says, prepare the surfaces meticulously.

krems81 

Sounds promising. Would you trust it? I’m not too familiar with the product and this would be a build for someone else to use as a reliable commuter

non-fixie 

For re-attaching a seat stay to the seat lug, probably not. But for a bottle cage, sure.

jackbombay

Hmmm, I would certainly use it on my own bike, on someone else's the stakes are a bit higher, but its quite tough, JB weld website claims a tensile strength of 3960 pounds per square inch of adhesion surface.

JohnDThompson 

Not with a fuel/air torch; it would take too long to get up to temperature and cause extensive paint damage. To do it properly, you'll want fuel/oxygen and a high silver content rod. But before that, I'd try JB Weld or something similar, as suggested above. If it fails, you're no worse off than you are now, and can always use a clamp to hold the cage in place.

bark_eater 

Theres a black locktite thats used for gunsmithing as a basically a silver solder replacement. I think you need a very clean surface for that kind of non gap filling glues.

repechage

Wild, maybe a touch of silver at one point of the diamond, maybe, otherwise when flux becomes a structural bonding agent.
mask off well and often, abrade surface, the boss side will be the trick. Picklex 20? (too expensive)

thread a long bolt into the boss as a handle , run a nut to secure, and go at it with a wire wheel on a dremel?

Spaghetti Legs 

You can look into a rivnut. That’s how the bosses are secured on my aluminum TT bike.

Edit - rather than bosses, I should say it provides a threaded insert for the bottle cage bolt to secure directly into.

https://en.wikipedia.org/wiki/Rivet_nut

brian3069

Maybe it can be reattached with a rivnut.

Mad Honk 

The clown-eye or diamond boss looks like it didn't have any brass under it. You could try cleaning the parts with a Dremmel tool and epoxying the part back in, but even with 2800 psi epoxy it would be weak. If you have a new clown-eye you could use a riv-nut, or even drill the old boss out of the clown-eye and then riv-nut it in. Some epoxy or JB weld under the eye and then touch it up with some enamel paint. All are work arounds, and not as good a re-brazing. But should hold under normal conditions. HTH, MH

SurferRosa

Using a rivnut would ruin some aesthetic. Does the bike warrant aesthetic?

Is it the top or bottom fitting? If bottom, a simple fix, like jb-weld, will probably last longer there.

As non-fixie said, prepare the surfaces meticulously for the epoxy. Use tape on the paint. Follow the jb-weld instructions. Just buy the regular stuff. No need to go overboard.

obrentharris 

It looks like it was held on for all these years by nothing more than the paint. The JB Weld will be much stronger.
Brent

thumpism 

I'd use JB Weld and make sure I squished a little down into the tube to sort of "wrap" the binding stuff over the edge of the hole in the tube, like they do in "plaster and lath" walls. Oil the threads on the screw so it does not get stuck.

repechage

Rethinking- Rivnut and a reuse or new diamond "stiffener"
Bringhneli, nova, ceeway, possible sources. JB weld and Rivnut it together in one swoop.

I wonder if there is any braze holding the stiffener to the threaded insert.

Manny66 

clean it til you get bare metal, JB Weld and your done.

Hudson308 

Yep

fishboy316

Clean it and use JB. As stated before if it does not hold you are no worse off than now. Jb is tough stuff!

Russ Roth

Clean meticulous and install a river nut then grind down the backside of the diamond and drill it out the center so it can slip over the rivnut. Little light epoxy to hold it in place. It'll be purely decorative at that point. Paint the edges to keep it clean.

madpogue 

If it's one of two sets of bosses, you could at least use this set just for a pump, and use the other for a water bottle. I would be.... cautious about the weight of a full water bottle attached to this boss JB Welded to the tube.

Schwinn MTB?

krems81 

Thanks for all the suggestions everyone. It was the bottom boss so I tried JB Weld. It’s been curing since yesterday so I’ll have a look today. Hopefully all good. I’ll update once I check it out