Celika

Hello !

I'm looking for a budget "frame assembling" way (~450€ max all included), more adapted than my MMA inverter wich is very hard to use for steel under 1,5-2mm thin.

I plan to build cargo bikes, trikes, customise MTB/road bikes, and accessories, from recycled old bike, scrap metal, and sometimes good tubes.

I have thought about a TIG torch for my inverter, but it seems quite "poor" compared to a real TIG (scratch start, no pre/post gas, big gas consumption, no pedal...). Plus, Argon is pretty expensive in France (2,3m3 bottle cost about 350€ brand new, reload cost 100€).
The MAG with Co2 seems borderline on thin steel because of high penetration and poor control.

So I've heard about the butane/propane instead of acetylene, with oxygen - or even better a oxygen concentrator. No high pressure gas, some investment at the begining but cheap to run and easy to refill,... I've made search about it, and it seems to work quite well to braze bikes.

There is some questions that my search didn't answer surely:
-It seems you can use a "classic" acetylene torch, in size 0 or 1. To run butane is a larger tip ok, or a tip with multiple hole is really better ?
-Do you use a flashback arrestor with the oxy concentrator (low pressure, not that much OČ) ? And for the propane/butane, are all acetylene flashback arrestors fine (enough pressure ?) ?
-What kind of regulator do you use for butane/propane ? Is something like that fine, or better have a manometer for higher precision ? Basic adjustable regulator
-Do you think brass brazing only will be strong enough for a cargo bike ? I'd like to build a rather lightweigh version wich support about 80kg weight + pilot.

To finish, I already have a cargo made with MMA from scrap metal, but welds are... bad (ugly look, inclusions, variable penetration...). It seems they're strong enough yet (rode more than 300km, tested with 80+kg), but I'm not totally confident. Do you think it could gain strenght by fillet them over the actual welds ?

Thank a lot for your advices !

unterhausen

Brass brazing is fine for all bikes. I know Doug Fattic has answered your other questions, but I'm not sure of the answer. One issue is that oxygen concentrators are probably in short supply right now. And propane uses more oxygen than acetylene.

David Tollefson

You can use an acetylene tip, but propane-specific tips will retain the flame better. I modified an acetylene tip by making a very small countersink around the hole, and it works much better than it did previously.
I use a flashback protector on the propane side only. No need for one on the oxygen contentrator.
A two-stage regulator is the way you'll want to go.
And yes, bronze will be plenty strong so long as you get good penetration with a nice internal fillet and goo throat depth on the external fillet.

Doug Fattic 

I might add that multi-port tips were designed for use in the jewelry trade for precision. In the States some of us finally convinced the Paige Tool Company to make adaptors for American torches with inch threading on their miser/elbows. Their tips are awesome. In the UK, Welder's Warehouse supplies multi-port tips to fit their imperial threading. I don't know about multi-port tips that fit European torch handles.

Celika

Thanks a lot for your answers !

So I'll try to find a multiple-port tip.
Good idea to look on the side of jewellry/glass pearls makers; in Europe it seems they are the most common users of propane + concentrator (but I don't know how much this application is different of fillet brazing a bike, in term of heating, gas flow,..).

It's used in plumbing too, but not that much (a lot of mini cheap kits with super expensive disposable bottles, some conversions from oxy-acetylene). In fact, this process isn't well known here (just as CO2 MAG for steel).



Because of the pandemia the medical device maintenance companies are really busy, but I had a contact with one near to my location that could have some concentrators no longer usable for medical application to sell; I'm waiting for news and prices. The funny thing is that the seller itself use a concentrator for oxy/propane brazing.

I looked for a 2 stage regulator with 1-4 bars output, but it's not common at all in Europe (as oxy/prop is not used, and usual applications only require single stage or low pressure), just found this one in UK wit a limited output pressure. I'll continue to search, and maybe buy a single stage if I don't find better.

So for my current cargo, the lack of penetration of the fillet between and inside the tubes should make fillet not realy effective ?

guy153

MIG/MAG will be fine on 1.5-2mm, probably using 90% or 95% Argon. Certainly much easier than MMA. If you want to do chromoly tubes (around 0.6mm to 0.9mm on bikes) you need TIG with a foot-pedal. Many cheap mild steel bikes are MIG welded from the factory, often by robots.

The brazing idea also sounds fun, but MIG is probably easier and will make nice strong joints.

Celika

Hi

A good MIG cost about the same as a decent TIG (about 350-400€ new, there is even a nice Stahlwerk AC/DC TIG for 500€), and argon/CoČ is not so much cheaper that 100% argon right here.
I guess the gas cusomption is lower as the welding speed is higher with the MIG, but I was mostly interested of MAG with Co2 because it's super cheap and easier to get (from pub, or even Co2 extinguisher). Apart from that, even if it's harder to learn, I'd prefer get a TIG (slower but more possibilities).

Plus, I'm looking for perhaps become professionnal framebuilder in some time (I need a looooot of learning and practice before), the TIG or brazing is more used.

I'd like to be able to build cromo frames too, I already have some old MTB cromo frames and a road Columbus Thron frame to modify/recycle. And thin tubes accessories like racks.

unterhausen

Since it sounds like you are biased towards TIG, I think you should save up and get that.

guy153

Agree much better to go with TIG than MIG. The argon lasts quite a long time. 5 or 6 litres per minute is plenty for practicing and making furniture, bbqs, etc (which is all also practicing but I turn it up a bit higher than that on actual frames just to get shinier welds and to make sure.

​​​​​The Stahlwerk machines are indeed very cheap and I guess AC might be useful if you want to make aluminium racks. But if you do get a TIG you should also budget for a foot-pedal and a number 9 CK torch with a flex hose. These are quite pricey but make life much easier for delicate work like bike tubes. A lot of people use pulse TIG for bikes but personally I prefer to just use the pedal. And you only need about 80A max so the cheaper machines that max out at 160A or so are fine.

I seem to have hijacked a brazing thread to go on about welding so apologies for that...
​​

Celika

You're welcome, it's interesting to have advices and opinions .
Pedals and flex torch seems indeed to be really practical. The Stahlwerk exist in kit with these two accessories (400€ for DC ans 650€ for AC/DC), but I'll see in a few years if this model stay reliable and if better offers appears on market.

@unterhausen: I'm not focused on TIG yet, I plan to buy a good one when I will have a large enough workshop, and after following a training, but for the moment I haven't a lot of space and prefer stay on a more economical system (furthermore the torch would be usefull for general DIY: bend metal, plumbing, forge or temper some parts, melt aluminium..); if it allow me to make strong "welds" on bikes and is not too hard to learn I'm fine with it. I'm quite fan of big round fillet on bikes too.

guy153

It's not so much the flex head on the torch that's important as the cable. The CK torch comes with a special red cable that is really flexible and light and doesn't tug on the torch or get in the way. This is the game-changer IMO and I actually use a No 9 torch without a flex head. With the torch so small and light and the cable not pulling on it you can hold it how you like fairly easily.

Most machines you buy come with a standard cable and a bigger No 17 torch with or without a flex head. Fine for general fabrication and welding in straight lines.

Doug Fattic 

Oxy/propane is a great tool to start learning how to put tubing together. It is slightly easier to learn with oxygen/propane than oxyacetylene because if has a slightly lower flame temperature. That gives the beginner a little more time to understand and react to what is going on in the joint. For the same reason it is a bit easier to start out with a tip that has a smaller orifice (hole). Because it produces less heat volume, it takes longer bring up a joint to the proper brazing temperature and as a result gives the operator more time to adjust the flame for proper control. As your skill and understanding of what to do increases, you can use bigger tips. I can use either when making a frame without having to think about it. I use bigger tips with propane to compensate for its lower temperature.

Learning to coordinate your left and right hand while brazing with a filler rod and heating torch will be helpful if and when you decide to learn how to TIG weld. And if you want to start making frames, there are some places where brazing is better than welding so it is a foundation skill you will want to have.

Celika

Hi

Thanks a lot, I'll give a try for it !
@Guy: ok thanks, the big idea is to get a smaller and lighter equipment to be more comfortable on precice welds, on tubing,... I'll keep that in mind for the day I'll begin to search a TIG .

Celika

Hello !

Since my last post, I've buy a 2nd hand 1m3 O/A setup (cheap, but the bottles won't last long).
I'm still trying to build an oxy/propane to run cheaper and complete the O/A, but really don't find a propane regulator around 1,5-7psi, not too expansive (under ~50€), and compatible with european propane tanks like that:


It seems it's a 1/2" left threaded.
So I've thought to use an acetylene regulator, as it's more common, cheaper, seems like it works quite good, with propane and I have an old one unused, but I still can't fit it on my bottle. I've search for adapters but don't find it on the net. Do you have some references or links ?.. Maybe use 2 adapters (bottle => 1/4" + 1/4" => acetylene) ?

Thanks for your advices !