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 !