Brazing, soldering lugs…Turbo Torch?

[Applesauce]

Kinda stupid question time, probably… I’m kinda slowly brushing up on my frame-building knowledge after many years away from it. I don’t remember what I don’t know about it all. I’m currently stuck on: why oxy-acetylene/oxy-propane, and not just air-acetylene? Obviously the answer is temperature, but I feel like there must be some more to it than that. Controllability? Obviously the answer is that pure-oxygen flames are superior, because that’s what everyone uses. I’m just curious why?

I’m asking partly because I have an air-acetylene Turbo Torch for plumbing (copper and brass mostly, sometimes some steel), and it seems to get plenty hot. 5500° F ish? And it’s a big, brutish flame that seems to me would be great for lugs, whereby one could get a whole whack of metal up to temp at once. But I know there’s something wrong about this idea, because no one does it. (I’m smart enough to know I don’t have some kind of solution that no one else has ever thought of. ;)) But…why?

Thanks, sages.

[e-RICHIE]

Kinda stupid question time, probably… I’m kinda slowly brushing up on my frame-building knowledge after many years away from it. I don’t remember what I don’t know about it all. I’m currently stuck on: why oxy-acetylene/oxy-propane, and not just air-acetylene? Obviously the answer is temperature, but I feel like there must be some more to it than that. Controllability? Obviously the answer is that pure-oxygen flames are superior, because that’s what everyone uses. I’m just curious why?

I’m asking partly because I have an air-acetylene Turbo Torch for plumbing (copper and brass mostly, sometimes some steel), and it seems to get plenty hot. 5500° F ish? And it’s a big, brutish flame that seems to me would be great for lugs, whereby one could get a whole whack of metal up to temp at once. But I know there’s something wrong about this idea, because no one does it. (I’m smart enough to know I don’t have some kind of solution that no one else has ever thought of. ;)) But…why?

Thanks, sages.

When we started making frames at Witcomb USA we used Turbo Torches for several months. We jettisoned them because they may heat well but lack all other attributes needed to coax the filler material through and around the basic joints that make up the confluences of a typical bicycle frame.

[Applesauce]

I think I get it. So while you might be able to get the whole thing hot, if for some reason you didn’t, you lacked the control to get a smaller region hotter?

[e-RICHIE]

I think I get it. So while you might be able to get the whole thing hot, if for some reason you didn’t, you lacked the control to get a smaller region hotter?

the tips are changed for the heat coverage desired.

how to explain this?

better to just say that the turbo torch process isn’t framebuilding compatible.

one and only one exception might be steering column to crown assemblies.

[Mark Walberg]

I built my first frames in the early 1970s using acetylene and air with a Smith torch that made a pretty big flame. I learned how to do this by going to the local welding shop and asking a guy what I needed to braze a frame. He showed me by brazing a seat lug to a short piece of Reynolds 531 that I had brought with me. This setup worked to build quite a few frames. When I switched to acetylene and air, I found much better heat control, and I was much less likely to cook a joint by getting too hot. It is certainly doable without the O2 though. With practice (like anything else) one can get good at it.

[Doug Fattic]

Applesauce, your instincts are correct that an air-acetylene Turbo Torch has some of the qualities but not every quality needed to properly braze a lug. If you could start with it to warm up the work evenly so the tubes and every part of the lug came up to brazing temperature nearly all at the same time, that would be great. Then you have to add just the right amount of silver or brass. So far so good, but getting that exact right amount in and removing any extra out (to get clean shorelines) requires a fine sharp flame.

Most often this question of alternative brazing equipment comes up as a way to avoid the expense of getting the best tools. It is possible using a BernzOmatic "cutting, welding and brazing" torch kit. I'm not sure they make this unit any more. The torch handle is designed to use propane as a flame fuel (because the orifice diameter is about the right size for general frame making and has a recessed tip that propane needs). And it has a twin hose so oxygen can be added. There are actually better small kit brazing options available on Amazon with more controls. If you are curious I can write about them in a seperate post. The problem is not with the small propane cartridges. They contain enough fuel to make a frame. It is with the oxygen cartridges. When I've timed how long they last, it is about 9 minutes so you would be using too many to make a frame affordably. IMG_1074.JPG

What you can do is find a used oxygen concentrator. These are the units that take atmospheric air and turn it into almost pure oxygen. They are designed to keep grandma alive near the end of her life. Finding them cheap is trying to get one after she has passed. I got one of mine from a guy that works in a nursing home. Typically on Craigslist they go for $200. I've had students that have found them with a bit of luck for less than $50.

[bulgie]

Not much to add beyond what Doug has said, he's the guru of O2 concentrators for brazing. But I just thought I'd add another vote for 'em. "Free" O2 for life! OK you pay some for the electricity, but no more going to the welding gas store for bottled O2.

In the Old Country in the bad old days they would hearth-braze with "town gas" and forced air from a squirrel-cage fan, but the flame was low temperature, so you needed a pile of fire bricks built up around your joint to hold the heat in close to the joint. The entire joint would get hot enough to flow brass, but little ability to guide the filler to where you want it, or ability to turn the frame to all angles to make gravity work for you instead of against you. That they were able to make good frames that way amazes me, but that's no reason to use 19th century techniques in the 21st, when much more excellent methods are commonplace and cheap.

Shopping story: I had a shortcut on my desktop going to Craigslist with the search term oxygen concentrator, and I checked it nearly every day, or once a week at least, probably for more than a year. There were always a handful of choices, but I wanted a really cheap one. Maybe that sounds like a lot of work, but it was ~ten seconds per. Finally found a guy who had two, wanted $150, as in $75 each, and one of them was a 10 liter/minute. FYI 5 l/m is far more common, like 50x more common — 10 l/m units don't come up very often, and when they do they are frequently $800 or more. But don't worry about that, 5 l/m is plenty, I'm just bragging about my good luck. Both of mine worked perfectly, needing nothing more than replacement air filters. I passed my extra 5 l/m on to another amateur FB. The moral of the story is be patient, if you have the time. If you're in a hurry you might need to spend more, but there are always options.

Since they are medical devices, with stringent requirements (not letting Grandma die), there don't seem to be any bad ones. They're very durable.

Has anyone here ever got stuck with a bad one? I've never heard of one going bad, but the number of people I know who own them is small. But it seems to me from my limited experience, buying the cheapest one off CL is reliable enough. They're being sold because the patient "aged out", not the device.

I have heard that the sieve that separates out the nitrogen can be 'repacked' or some such (I forget the word they use). Even one that doesn't produce good O2 anymore can be rebuilt. If the compressor went out, and needed anything more expensive than a new gasket, I might just go back to CL to find another entire concentrator cheap. Although the compressor rebuild kits are reasonably priced and the video I watched on rebuilding one looked quite do-able for a shadetree mechanic, no expensive specialized tools needed.

[Thomas Norton]

So I have a concentrator. But never thought of changing the filter!

[Matthias]

The simplest answer I can think of is 'concentration' or 'density'. Flames that consume the same amount of fuel gas will put out the same ampunt of heat. But the flame that relies on ambient air occupies a larger volume of space in doing so. So for the same amount of heat the operator will have less ability to focus the heat where they want. And this is part of the premise of artisanal construction: This amount of control paired with the craftsmans skill is claimed to result in a superior joint.
A lugged frame certainly can be built using a polar opposite heating method. Stick a bunch of frames together with brazing alloy preforms in jigs and chuck them all into an oven. Bring them all up to the required and uniform heat. If the whole process is very controlled throughout good joints will be produced. Otherwise quality might be spotty since you relied on conditions to be exactly such that the alloy will flow evenly through the joints. But no one was there to watch and confirm it really did and make adjustements where needed. Having a craftsman do they job ensures this.

[Applesauce]

I get it, thanks all. I will get a proper outfit, and keep my Turbo Torch and B-tank for work.

Pretty sure the frame I’m still riding I put together with oxy-nat gas, but I don’t remember for sure. I have the vague sense that propane and nat gas produce smaller, more precise flames than acetylene. Disabuse me of that notion? I don’t know where I got it. I’ve been reading, but my reading is clouded by things I think I remember from former lives.

I’m leaning toward acetylene, at least partly because it seems fairly “standard” (eg, for tips, hoses, regulators), and because I don’t have any trouble getting it. Have I missed some other reason to go with propane? Or nat-gas, for that matter?! I’m a plumber: I could easily run a <2 psi gas pipe out to the garage. But it would be coming from the rest of the domestic service, which I have no intention or desire to modify.

An oxygen concentrator seems like a neat idea. How much complication does it add? (Doug especially, please don’t rewrite information you’ve already provided on the VS: I’m slowly working through it!) I likely will not build a huge quantity of frames, getting oxygen will not be tough for me to get, and I don’t need a weekend nightmare trying to get a concentrator to play nicely where a standard tank and regulator would normally be. I come from a very healthy family: I have no familiarity with such devices. But then, if it’s truly plug’n’play with an oxygen-acetylene setup, it seems like a no-brainer.

[Mark Kelly]

I have heard that the sieve that separates out the nitrogen can be 'repacked' or some such (I forget the word they use).

The sieve is the material (zeolite) with which the exchange beds are packed.

[Doug Fattic]

Applesauce, the typical person seeking advice on a framebuilding forum is a hobbyist with most of his play time on weekends. They tend to place a high priority on doing things the least expensive way. For them propane with an oxygen concentrator is the way to go. Buying both an acetylene and oxygen tank with regulators is a big purchase and a barrier to getting started. And refills can only be done during banking hours. Propane is much easier to transport and many times cheaper to buy and refill. And the stores that sell them are going to be closer and open most hours. And a concentrator (that doesn’t need a regulator) is a buy once and forget about it for years until you need to change the filter. They are designed to run constantly for thousands of hours. And they are safer too. The one disadvantage is that you have to let it run a few minutes to purge the line so mostly pure oxygen is coming out. Buying the right elbows and tips for propane is no different than buying for acetylene. Just get the right ones.

It doesn’t make sense for most pros to switch over to propane when acetylene works perfectly. They already have all their equipment and can take off in the middle of the day to exchange tanks. Some builders like Andy at Strawberry has used propane for 50 years. I used acetylene for 30 years before I switched over about 20 years ago. I knew that most of my framebuilding class students would want the cost savings and convenience of propane when they were setting up so that is why I promote it as a fuel for beginners.