Furnace brazing bike tube experiment

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us56456712

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I’m thinking of building another Breezer 1clone. Problem is no cheap mixte available to cut up for the laterals. Here is another crack pot idea of mine. Hey, I have a lot of frames with the correct diameter seat stays, but I need to make three of them into one. Here is my recipe. Cut them off with a pipe cutter, thread the insides so small brass nipples from the hardware store can be threaded inside with some brazing flux melted onto the nipples before threading the pieces together. Clamp them in angle iron so their absolutely straight. Then tack weld them so they stay. Put them in a hardwood fire until cherry red, sprinkle on more flux, use a propane blow torch to add air and hot gas and the brazing rod easily melts. Leave it awhile and turn in the coals with torch assist in distributing the melted braze. A bigger fire in the summer would be better. I have turned pipes cherry in the summer in my fire pit so I’ll do more experiments when it’s not -20C and blowing hard from the north. I don’t think I’ll need torch assist with a bigger fire. I could use my shop vacuum, attached to a pipe, to blow on a big fire in my pit, really get it hot.

Here are the inside the tubing threaded cut off stays and the $1.19 brass fittings.
31E06B8E-2AB1-44D7-89D1-3CDBC898622A.jpeg


Here it is screwed together and clamped for tack welding
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The small maple fire in my smoker.
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After furnace brazing. Isn’t being retired great!
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us56456712

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Oh, nuts, setback, false start. The first brazed joint filled in real well. I filled in the gouges in the tubing where I clamped it for threading
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The second joint got red hot and the tack weld bent because I decided to file it down before brazing. This was a mistake, I made it too thin and it burned through. A tack on opposite sides will be tried. I’ll thread the other ends, tack it without filing and try more furnace brazing.
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I was gonna suggest a bellows to boost that heat--the Shop-Vac exhaust is even better! Not so sure how those temps may affect temper of the steel, though.
 

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I was gonna suggest a bellows to boost that heat--the Shop-Vac exhaust is even better! Not so sure how those temps may affect temper of the steel, though.
They furnace braze bicycle frames still today. Vintage Raleigh and the vintage British motorcycles frames were furnace brazed as were early Italian and other frames. It’s all they had through the 1920s and the British kept doing it for years as it was cheap and fast. It did cause some problems with metal hardening and brittleness but this was usually wasn‘t a problem. It could make threading and facing hard to do but this was unusual, so a frame maker told me. It’s a problem if it cools too fast. Furnace brazing thin modern high quality tubing is probably not a good idea. I think it will be ok for what I’m doing, as Long as I don’t drop it hot in the snow. I’m wondering how strong a brazed butt joint will be after the braze and tack weld are flat filed. That will really be the test.
 

Couch tater

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Looks like a fun experiment and a good way to try staying warm while working.

If you don't get the results you are looking for, that is an ideal spot for a plug weld. The joint could be filled with solder after welding to make it all invisible.


 

us56456712

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Looks like a fun experiment and a good way to try staying warm while working.

If you don't get the results you are looking for, that is an ideal spot for a plug weld. The joint could be filled with solder after welding to make it all invisible.



Ive done quite a few plug welds, but I never new it was called that. It would probably be stronger and easier if I threaded a cut off steel bolt in the joint, plug welded them and then brazed the joint. I think I’ll try it on the other joint, thanks.
 

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I drill into the inner piece no deeper than the taper of the drill center so it is a concave hole. I think it makes a little stronger weld.
 

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It’s flat filed and still together. The tubing sagged a little from the heat, but away from the joint. I should be able to straighten it. I threaded the tubes again and used a cut off section of a bolt to thread into it. It’s too cold to try a plug weld, like -18C. Update, I just straightened it easily over my knee. I’m staying with the primitive theme.
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This gap is what has to be filled with brazing.
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Thanks Couch tater, that plug welding idea was just the ticket. I used such short pieces of bolt threads that the holes drilled for the plug welds were at the very end of the bolt.
68CEBE77-697E-4AD3-96BE-1820E48277F2.jpeg

The plug welds are strong, they won’t let go when I furnace braze the joint shut. It’s too cold and stormy to get the smoker fired up today.
A407D5BE-56DF-46E5-ACB0-AEA2061A8ACB.jpeg
image.jpg
 
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I’ll have to do more experiments. The steel inserts and plug welds were harder to get the brazing to flow than when I used brass inserts and a bridge weld. The steel inserts probably took the heat away inside the joint with my meager fire. I would turn the tubing in the hot spot but the brazing wouldn’t flow. It took a long time. When I flat file it I’ll be able to see how well the brazing went into the joint. It’s all an experiment anyway so I’ll keep fiddling until it’s perfected or just another piece of my advice. I give lots of advice but I personally never take any of it.
image.jpg
 

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You can defiantly see the joint, when there was a brass plug the joint was completely filled, couldn’t even see it. I suspect the melted brazing seeped around the steel threads so I didn’t get a flush fill. It seems strong though. Next, I’ll try filling in the low spots with silver brazing, which has a lower melting point. More experiments. A lot of monkeying around to save a couple of hundred bucks or more.
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