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Post by wheelson on Oct 22, 2020 2:42:13 GMT
The Bernzomatic may be enough to do the bronze rod. You'll need 1000-1200 degrees F for the bronze rod, about 800 for most silver solder. I would recommend MAPP gas over propane for a bit more heat. If you can find one of the dual small torch setups that uses propane/MAPP and oxygen, you can do a lot of light brazing in addition to small repairs such as adding water bottle and cable guide braze-ons.
If I remember correctly, in brazing, the brass (bronze) actually forms an alloy with the steel. With the TIG silicon bronze, a very tiny bead fills the crack but really doesn't melt the adjacent steel as that would tend to make the joint brittle. I don't have any first hand experience with MIG, TIG, or steel welding, only brazing which I learned as a bike mechanic from the shop locksmith and the business machine repairman. 50+ years later, I'm still amazed how those guys could braze tiny safe combination and typewriter parts back together and fab some rather unique one-of-a-kind parts and tools.
As Jim mentioned above, there's a really good discussion on the subject going on over at the CR list. The exercise there is repairing a cracked bottom bracket shell casting without destroying the paint. I've been a member of that list for years and I highly recommend it. It's big, 4000+ members, but very friendly and diverse with a lot of mechanics, framebuilders, shop owners, you name it.
Best,
John "wheelson"
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Post by brianbutler on Oct 22, 2020 12:27:30 GMT
The Bernzomatic TS-8000 can also use MAPP gas. On Youtube (grain of salt media) I saw a comparison using different torches with propane and MAPP and a heat sensor. The results were the same for propane and MAPP but varied considerable between torches. So I'll give it a try with propane and report back.
"Without damaging the paint". Good luck.
Brian
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Post by brianbutler on Oct 25, 2020 3:04:52 GMT
The propane torch was hot enough to do a test brazing of some 1/8 steel rods but it was not hot enough to maintain heat over the tube area I need to repair the frame crack. Also, I believe bronze brazing requires some skills that I do not have. I don't understand its behavior. It doesn't seem to flow like solder.
For my next act, I will try silver soldering. According to the specs, it is as strong as brazing (70000 psi tensile strength). It is more expensive but I don't need much material. I believe I can add my braze-ons with this technique as well.
More to come.
Brian
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Post by cusqueno on Oct 27, 2020 14:35:35 GMT
Not sure if this is relevant, but here in the UK my father used to silver solder things like boilers for model steam engines - similar size to bike bb shells - using a simple blow lamp attached to an outlet on our gas stove (more about this below) and a homemade hearth built in some sort of cast iron basket with broken up firebricks - these are the things that are used to make open coal / coke or wood-burning fireplaces.
Initially the gas was 'Town Gas' - a poisonous substance produced from coal, a mixture of carbon monoxide and hydrogen. The UK converted to 'natural gas' - methane from the North Sea - in 1967. This was a massive operation as all existing gas appliances had to be converted to burn methane. Including my father's little blow torch. Can't remember if it was actually converted or they simply gave him a new one. Anyway, he continued to silver solder using methane.
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Post by brianbutler on Oct 27, 2020 21:25:37 GMT
I was successful (but not very neat) with the silver solder and propane. I extended the brass fillet with silver solder, which also flowed into the crack. It feels quite strong but looks a mess. I have a few blobs of solder where the tube was cold and some other problems. I can file these out but I might try melting them smooth with the torch. I am going to try soldering some cable guides and water bottle bosses. I think they will be easier than mending the crack because it will be a smaller area to keep hot and more easily accessible. The propane torch is plenty hot for silver soldering.
Cusqueno, thank you for the advice.
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Post by wheelson on Oct 27, 2020 21:43:44 GMT
Great news, Brian. Neat and fillet brazing (or silver soldering) don't always happen simultaneously. Most fillets get filed, the king of "near net shape" fillets was supposedly Tom Ritchey. I read that he brazed frames together freehand.
Schwinn did some fillet brazed frames in the '60s - '80s, even before. I have a Schwinn Town & Country tandem from 1948. It was fillet brazed, then the joints were "leaded", a process used in older car making in which molten lead was used to fill less than perfect braze or weld joints for appearance. In fact, my powder coater called me when I had the tandem frame refinished to tell me he suspected lead, then did a test heat and indeed, the lead melted out. I'm glad he did, the curing temperature for the p.coat is 400dF which would have melted the lead and ruined the p.coat. You have no worries with silver solder, though, I believe the melt temp is around 800dF.
I'm glad you're marching on with the Middlebury.
Best,
John "wheelson"
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Post by brianbutler on Oct 28, 2020 0:19:56 GMT
John, I believe the Schwinn Superior was fillet brazed Reynolds 531 (or something equivalent.) Schwinn did not tout that feature like they should have. Instead, it got confused with the other smooth jointed "electro-welded" frames like the Continental and Varsity. On the other hand, those electro-welded frames and Ashtabula cranks with the 3/8" ball bearings are absolutely indestructible.
Brian
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Post by wheelson on Oct 28, 2020 3:11:05 GMT
Since I started my bike life in an old Schwinn shop in North Carolina in 1966, I've grown attached to Schwinns (for better or worse). I have a '78 Superior frame/fork hanging in my garage as a future project. Not sure what I plan to do with it, it would certainly make a great all roads bike. The Superior and the Sports Tourer, as well as the Super Sport, were definitely in a class above the "electro-welded" frames. The Super Sport was the unfortunate "step-child" in that it had the great fillet brazed frame but was stuck with the Ashtabula crank.
Best,
John "wheelson"
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Post by oldroadietehachapi on Oct 28, 2020 5:33:00 GMT
I was successful (but not very neat) with the silver solder and propane. I extended the brass fillet with silver solder, which also flowed into the crack. It feels quite strong but looks a mess. I have a few blobs of solder where the tube was cold and some other problems. I can file these out but I might try melting them smooth with the torch. I am going to try soldering some cable guides and water bottle bosses. I think they will be easier than mending the crack because it will be a smaller area to keep hot and more easily accessible. The propane torch is plenty hot for silver soldering. Cusqueno, thank you for the advice. Sounds like a fix! Anxious to see the result.
Jim
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Post by systembuilder on Jan 9, 2021 22:25:07 GMT
I have a suspicion that the "Birmetals" rim in the photos is actually made by Birmaluxe. I think I have exactly one Birmaluxe dimpled Weinmann Alesa-copy rim if you are looking to match a set. Mine is indistinguishable from a weinmann alesa dimpled rim, other than the stamping. I think that a similar rim was also sold by Milremo.
- Don Gillies
gillies@ece.ubc.ca
Palo Alto CA
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Post by brianbutler on Jan 9, 2021 23:25:36 GMT
I have a suspicion that the "Birmetals" rim in the photos is actually made by Birmaluxe. I think I have exactly one Birmaluxe dimpled Weinmann Alesa-copy rim if you are looking to match a set. Mine is indistinguishable from a weinmann alesa dimpled rim, other than the stamping. I think that a similar rim was also sold by Milremo. - Don Gillies gillies@ece.ubc.ca Palo Alto CA Thanks, but neither of the rims on this bike are good enough to keep and probably not original. I have a bunch of other rims.
Brian
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