Airburst

I'm fairly sure I saw a reference somewhere to someone building frames from fairly high-end tubing using gas welding, but I've no idea where I saw it, or who was supposed to have built them. I was under the impression that gas welding didn't work reliably for thin metal, but I definitely remember the bikes being described as "gas welded"... Am I missing something here?

NoReg

Somewhere in the forum there is a link to a pro builder who gas welds frames. I couldn't find it. My recollection is that it was quite a few years back. I started searching around '06, but didn't find anything.

When it comes to bike tubing, there is the upper end stuff like 953, that at least at some point, they only sell to highly regarded builders, and that they surround with a lot of interesting speculation when it originally comes out. That stuff is not going to get a factory blessing for gas welding.

Then there is the low end tubing, which rocks for a lot of building, 4130 type stuff. That thin wall tubing was originally intended for gas welding, that was all there was for half a century or more. It is easily welded down to .028" I suppose one can go thinner, but it probably wouldn't be required. There is still some bias in serious circles towards gas welding this stuff.

In the middle range there is stuff that is sometimes complex in composition, where it might have odd properties, and require a welding wire that was not supplied in a gas version, or might have a flux need. I'm just saying, I don't know what the requirements would be or where one would go to find it. I have TIG, so I would go with that.

There should be a larger heat affected zone with gas welding, but if you follow the outline above, it isn't going to mater, 4130 can be welded without flux or other concerns.

There is the aesthetic issue. Even at its best, a gas weld tends to look less lovely than a TIG weld, but I don't really care about that myself. My main interest was getting people into a cheaper and safer way of building bikes, when I did my tests. There is no pulse with gas, and the dimes tend to look runny, and kinda sad. There are also blobs sometimes, even in quality welding. with TIG, these would be bad, probably cold welds, but with gas you can build filler much more freely, and sometimes blobs are just there for cooling. I don't know what a really great gas welder, trying to do pretty work could achieve though, The aircraft guys don't put their welds out there as do bike guys.

Finally, there is the heat distortion issue. There is more heat affect with gas welding. So that makes controlling alignment harder. this is going to make it even harder with the upper level, paper thin tubes.

unterhausen

I have seen references to someone building with o/a welding, but I don't remember the builder. People dabble with this, as well as mig, but I can't imagine it being a particularly good thing from a marketing perspective.
I would think that distortion would be really difficult to control. With tig you can use heat sinks effectively, with gas it's a lot harder since you would be fighting the heat sink the whole weld.

tuz

It seems Reyhand in the 30s in France gas-welded frames. Check that gallery. But yes I've heard too of a (contemporary) builder gas welding frames... can't remember.

NoReg

It's in this forum somewhere, I just don't have a smart enough search capability. I got the url from someone else, and then I think I repeated it a few times also. The guy's work was nice enough. As you say, hard to make it a big selling point except to take on the deficiencies of other methods. That case could be made, but not without having to overlook the whole better than good enough thing. Or the whole better on some points and not on others thing.

bobbotron

I believe Thursday bikes did/does gas welding for some of his bikes. Dr Welby (on MTBR) has done one too, I believe, as well as some custom lugs. I took an O/A welding class, where we did a lot of gas welding. I think (if you had a lot of practice!) you could definitely gas weld a frame, and it would be solid.

tuz

Yes it's Jon Norstog from Thursday. Perhaps Dave Porter has done it as well? (or it was MIG?). I think you have to stick to 4130 and variants. Here is a pic. Check the bikelist listserv too.

Six jours

I've seen a lot of gas welded frames from that era, including top-end race bikes. But that tubing was usually thicker than anything we use today - most such bikes I've encountered were approaching 30 pounds, including single speeds. There were/are exceptions, though...

NoReg

Ultalights are gas welded out of .028, which is fairly light. This one is mostly .028.

https://www.youtube.com/watch?v=VBWLN4w_PRU

moto367

I don't want to steel the thread, and pardon if this is a silly question but what is "gas" welding? Initially I just figured you guys were talking about brazing with o/a. Couldn't find a definitive answer on line either.

NoReg

Gas welding is using an oxy-fuel torch to weld together some metal. This is the original method for joining aircraft tubes as per Fokker of WWI aircraft fame. It is very similar to TIG welding except it uses the flame of the torch to fuse the metals together instead of an arc. The flame is adjusted so that it will not oxidize the metal being welded, and the blanket of the flame functions much like the blanket of shield gas with TIG or MIG. Some metals require a flux to also help protect the metal, but 4130 steel does not. Brazing is different because the union is formed from a metal that is not the same as the parent metal, and that metal has a melting point above 700 degrees. The joint is pretty much always prepped with a flux when brazing.

By the way, you can weld heavier metals that 4130 tubing, and gas welding is a good method around the farm in the days before cheap stick welders, or even today.

clasher

Gas welding is a totally under-appreciated skill these days... good torchwork is essential to mastering the other welding forms in my opinion.