Framebuilders - Torches...

Right, I know I've gone on and on about building a frame for about 2 years now, but I've finally decided to pull my finger out, so to speak, and actually do it. I've got the time and hopefully the money now, so I'm going for it. My grandfather is offering me his acetylene torch, hoses and regulators, and in order to make it work, I plan to hook a household propane tank up to the acetylene hose, and a compressor to the oxygen one. Acetylene is almost impossible to come by in the UK, as is high-pressure oxygen, but propane tanks and compressors are much easier.

Firstly, am I likely to blow myself up doing this? Obviously, I'll need some form of valve to keep the air out of the hose with the gas in, and vice versa, but apart from that, I see it as being safer than oxy-acetylene because a) propane needs air to cause an explosion, unlike acetylene and b) it only uses one cylinder rather than two. However, I'm not an expert in this, so if anyone knows more about this than me, please feel free to shoot a hole in my theory.

Secondly, is it even possible? Will the fittings on a propane cylinder work with a hose for an acetylene one? What about the regulator?

Thirdly, will this provide a hot enough flame, of the right type, for fillet-brazing?

Thanks in advance

Compressed air will not provide the same effect as pure O2, I doubt it would work. You can re-purpose a home medical oxygen concentrator and use that to supply O2 for brazing with propane. You might also need to replace the gas hose with a teflon lined hose as propane is smaller molecule and will leak through and degrade hoses designed for acytelene.

This is dumb. Get the right gas for the torch or get the right torch for the gas you have. I would really advise you to invest in taking a class where someone can show you the basics of using a torch because your question really reveals how little of a grasp on the basics of safety you have and what it's like to work in a shop with explosive gases.

I say this as an ironworker and someone that worked a few years brazing heat exchangers with oxy-acetylene torches... so I don't have much experience at framebuilding but I am quite familiar with the tools of the trade and your idea sounds like a disaster waiting to happen... but hey, I'm just some random internet person so whatever, it's your life

/\ What he said.

OK, looks like plan B might be better. I've heard of people using small plumbing-type blowlamps fueled by MAPP gas to braze bikes, and I've got one, but it currently runs on propane. I can get MAPP canisters for it from the same place I got the propane, but will it work out at prohibitively expensive to fillet-braze a frame using them?

Yeah I wouldn't recommend using a torch for something other than its intended purpose.

As far as I know, the compressed-air/fuel approach was used traditionally, and with bronze filler. It's used with a brazing hearth and Mercian still brazes frames this way. I see kits on UK websites.

Some people gave been successful silver brazing frames with air-Mapp. But silver is $$$. And for the heavy crown and BBs it is barely sufficient. With a hearth it should work even with bronze. Not sure about fillet brazing; a small but intense flame certainly makes it easier, which is not what you are getting with those torches.

I use an oxy-concentrator and BBQ propane. Works really well. 3 frames so far, fillet brazed and lugged, bronze and silver filler.

We use oxy-mapp torches a lot for cutting so I imagine it would work well enough for brazing. I wouldn't try brazing with a mapp-air torch, they don't seem like they'd get hot enough to get good penetration on the BB and fork crowns that are much heavier than just tubing... mapp-air works well for soldering copper. They sell little oxy-mapp torch kits here for 70$ with little canisters... they'll get expensive if you do lots of brazing but for a hobby build it might do it, I dunno.

Don't they have welding supply shops in the UK?

I use an oxy-concentrator and BBQ propane. Works really well. 3 frames so far, fillet brazed and lugged, bronze and silver filler.
I would be interested in seeing pictures of that.

I hate to see people trying to use plumbing torches to build bikes. It's difficult enough to learn to braze without having to worry about getting enough heat.

I use an oxy-concentrator and BBQ propane. Works really well. 3 frames so far, fillet brazed and lugged, bronze and silver filler.

What's an oxy-concentrator, and where can I get one? Is it similar to a medical oxygen generator?

Edit, just googled it, I now know what it is, where do I get one?

Further edit, how many litres per minute do you use for brazing?

Rio Grande Jewelry Supply has one that have been altered from medical use to brazing use. Their item # is 500140. I think Pa Pa on this forum has written about his experiences with them.

Yup I got mine following after BF user PaPa. Found it used on online classifieds (from the family of a deceased elderly probably). I use the whole range of LPMs depending on the tip size (#0, 2, 4 & 6 Victor), but actually the flow bottoms out to a bit above 4 LPM, from perhaps the small kevlar hoses or the small J-28 torch body. I'd need a little extra kick to braze solid steel crowns and BBs with bronze fast, but I manage.

Here are some pics.

Something tells me the National Health Service isn't going to sell me one of those, so I may have to have one imported, unless anyone knows of a supplier like Rio Grande in the UK?

Also, if I do get one, will a fairly old oxy-acetylene torch work with oxy-propane? Hose issues aside, I mean.

Check out glass working suppliers, the concentrators are commonly used by them as far as I know.

Also, if I do get one, will a fairly old oxy-acetylene torch work with oxy-propane? Hose issues aside, I mean.

It's unlikely your acetylene torch will work with propane. Oddly enough different gases have different chemical properties. There are seals in the torches that propane can dissolve... acetylene seals are made to resist acetone, so they might not always be compatible with propane. Some torches are made for different gases, as well the regulators, and they will usually have it clearly marked, esp. on regulators "for all fuel gases".

I would really urge you to do some more research at an actual welding supply shop instead of the internet. Surely professionals (of any trade) still use oxy-acetylene rigs in the UK, find out where they get their stuff.

Personally I try to avoid jerry-rigging medical equipment when the right tools are commonly available (http://www.boconline.co.uk/how_to_buy/store_finder/store_finder.asp). I didn't notice anything on the BOC site about acetylene being a restricted substance but maybe it is... IDK. Surely if you have acetylene regulators, hoses and torches it makes sense to just go with acetylene as a fuel?

in most cases, torches will work fine. The regulators were probably not intended to work with propane. It's possible that a regulator rebuilding service would know. The most significant difference between propane/oxy and acetylene/oxy torches is that the propane torches have some accommodation to keep the flame from blowing out as easily.

I took an old Smith AW1A (a favorite for framebuilders) torch to use in Ukraine this month where we build frames with bottled oxygen and propane. It worked fine. This replaced a bigger Harris torch I had brought over earlier which had replaced some awful Russian thing we started out with. A propane tip (as I understand it) has a counter bored end that keeps the flame from separating from the tip. This tendency to separate makes adjusting propane flames more fussy and finicky than oxy/acetylene. It is sort of a two-step process. First I light the propane with it turned on just enough so the flame is still attached to the tip. Then I turn up the oxygen and now I can turn up the propane a bit more without it separating and then I adjust the oxygen again to get the right balance between the two. An oxy/propane flame does not have the cone distinctions that make adjusting oxy/acetylene so easy to do.

I go up a couple of tip sizes when using oxy/propane. For example I like using a Smith AW203 for small stuff and an AW205 for crowns and bottom bracket shells (they are roughly the equivalent of a Victor #0 and #1) when I am using acetylene. In Ukraine - where we are using propane - I use a larger AW207 (a standard tip – not one designed for propane) to get about the same output of BTUs. It doesn’t really take me any time to adjust to using propane instead of acetylene.

We used Smith AW1A torches with oxy/propane at Trek. The only alteration was to use a slightly larger tip with propane.

It's unlikely your acetylene torch will work with propane. Oddly enough different gases have different chemical properties. There are seals in the torches that propane can dissolve... acetylene seals are made to resist acetone, so they might not always be compatible with propane. Some torches are made for different gases, as well the regulators, and they will usually have it clearly marked, esp. on regulators "for all fuel gases".

I would really urge you to do some more research at an actual welding supply shop instead of the internet. Surely professionals (of any trade) still use oxy-acetylene rigs in the UK, find out where they get their stuff.

Personally I try to avoid jerry-rigging medical equipment when the right tools are commonly available (http://www.boconline.co.uk/how_to_buy/store_finder/store_finder.asp). I didn't notice anything on the BOC site about acetylene being a restricted substance but maybe it is... IDK. Surely if you have acetylene regulators, hoses and torches it makes sense to just go with acetylene as a fuel?


Not really, because I can buy a propane canister for much less than I can pay to rent an acetylene one. The same goes for using an OC rather than a cylinder. It's not that the "right" tools aren't available, just that I can't afford them.

And as for them using acetylene over here, I've never heard of it being done, all the welding seems to be done with arcs, of one form or another. I'd imagine that's because everyone's so terrified of getting sued that they'd much rather have cylinders of CO2 or argon, which are pretty much chemically inert as gases, than cylinders of acetylene and oxygen, which aren't.

Well good luck with that then.

Well good luck with that then.


Thanks, I'm fairly sure I'll need it at some point in this. Three people have said propane will work, two of them have mentioned actually doing it, one with several different models of torches and the other at a major bike manufacturer. One guy has said he uses an OC, and that he got the idea from someone else on here who also uses it. I'd say I'm in with a decent chance of this working, assuming I can get hold of an OC for a decent price. If there's any doubt about the regulator, I'll get a new propane one as well.

Thanks guys!

are there no welders etc in england no torch cutting going on this is strange by victor smith torch o 2 is 99. what ever pure to work

go mapp and silver

This is dumb. Get the right gas for the torch or get the right torch for the gas you have.

The most astute observation & best advice offered!

The most astute observation & best advice offered!
Not sure why you dug up this thread to agree with a post that was misinformed. There are many framebuilders that have researched this subject thoroughly, and none have found any reason not to go propane/oxy with an acetylene torch. Do you have contrary technical information?

When I posted I didnt notice the date. Niether was my comment directed at any one other than the haphazard opening post.

Acetylene is almost impossible to come by in the UK, as is high-pressure oxygen, but propane tanks and compressors are much easier...
Thanks in advance

I feel your pain...acetylene and O2 are impossible to come by in the UK?!!! Outrageous!

I can't use acetylene due to the acetone... but thankfully... propane / oxygen is more than sufficient for brazing frames and this is all our shop has used for 30 years.

Silver has gotten frightfully expensive but again, brass / bronze is also more than adequate for building all but the most exotic of frames and most of the bicycles made have traditionally used brass / bronze which is much more affordable.

I do not know why you are having an issue finding an oxygen supplier in the UK... it is rather essential for torch work.

What was wrong with the OP's post.

- I thought it turned out the consensus was wrong and that compressed air fuel torches exist. Therefore he isn't using the wrong torch, or at least not ridiculously so.

- The UK apparently controls compressed gasses more heavily, which is not surprising if one was to read many of the transit, storage, or municipal rules, and checked insurance riders covering domestic users, it would turn out a lot of what is happening is not legal over here. But people just do it. If for instance my gas provider was required to only give me my bottles if I stored them in my truck properly, I would never get them, and people with cars would pretty much not be able to modify their vehicles to carry them. Just depends on the state of bureaucracy.

- It turns out concentrators are also controlled in the UK due to free distribution under the National health scheme, They don't regularly show up on craigslist.

In Australia, as in the UK, it is illegal to carry an acetylene bottle in an ordinary vehicle. The solution is really simple: the gas suppliers run delivery trucks.

The problem with trying to use an oxy acetylene torch for compressed air / propane is that the stoichiometric ratios for the gases are all wrong. A mixer designed for one will struggle with the other.

The problem with trying to use an oxy acetylene torch for compressed air / propane is that the stoichiometric ratios for the gases are all wrong. A mixer designed for one will struggle with the other.The stoichiometric ratio of oxygen to fuel gas are 1.2 to 1 for acetylene and 4.3 to 1 for propane.

Mixing air with propane is a different animal. Largely because dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. (notice the lack of oxygen?)

Within limits, even with the different stoichiometric ratios, most Victor torches will accommodate different, select fuels just fine - we know this because Victor offers alternate fuel mixers and tips - as does Harris and few other manufactures'. However, these torches are internal mix - meaning the oxygen and fuel are mixed prior to leaving the tip. These torches are designed to be used with oxygen, not air.

Air/fuel torches are usually external mix - meaning the fuel and air are mixed at or slightly beyond the tip - such as the Bernzomatic. If memory serves, the stoichiometric ratio of these propane torches is on the order of 24 to 1.

Mixing air with propane is a different animal. Largely because dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. (notice the lack of oxygen?)

Within limits, even with the different stoichiometric ratios, most Victor torches will accommodate different, select fuels just fine - we know this because Victor offers alternate fuel mixers and tips - as does Harris and few other manufactures'. However, these torches are internal mix - meaning the oxygen and fuel are mixed prior to leaving the tip. These torches are designed to be used with oxygen, not air.

Air/fuel torches are usually external mix - meaning the fuel and air are mixed at or slightly beyond the tip - such as the Bernzomatic. If memory serves, the stoichiometric ratio of these propane torches is on the order of 24 to 1.

Great summary! I guess the answer to the OP's question is you can braze with propane and swirl-air combustion, but you need a properly designed torch. Again, I'm glad we don't have the kind of Nanny-State here (at least not yet) that they seem to have in Britain.

Great summary! I guess the answer to the OP's question is you can braze with propane and swirl-air combustion, but you need a properly designed torch. My intent, was to briefly explain why you should never attempt to convert or use an internal mix torch with any 'air' source, compressed or not. It won't work.

Internal mix (oxy/fuel) torches typically have two hoses - a red/orange designating FUEL, and a green hose designating OXYGEN

External mix (air/fuel) torches typically have only one red hose (or the tip connects directly to the FUEL bottle).

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External mix (air/fuel) torches typically have only one red hose (or the tip connects directly to the FUEL bottle).

Yes, that's exactly the type used by plumbers for sweating copper tubing...usually with an MC acetylene tank and a long hose...air is introduced via sized ports in the torch head. I tried silver soldering with this setup but it didn't work...just wouldn't generate enough heat to do a decent job. For precise work where the smallest standard Victor welding tip and their small handle didn't work, I got a micro-torch that I use on by acetylene/02 tanks (requires special low flow regulators for the tanks). This works superbly for the smallest and thinnest parts (e.g. brazing posts to derailleur clamp-ons, etc).

I haven't tried using air/propane for brazing, but I think there are some torches that are used by jewelers to braze small pieces.