[snip] he uses an oxygen concentrator. And the reason is he uses one of those mini torches. Anything bigger than that and I don’t think it would work.
I use an O2 concentrator for brazing, with either propane or acetylene. I've brazed some heavy-ish stuff, say up to ~1/4" thick.
When using acetylene, fuel is the bottleneck, not O2, due to the max withdrawal rate with acetylene, which depends on your bottle size. Most smaller bottles, like what a home user would have, don't let you use a very big tip, lest you exceed the max withdrawal. When that happens, the acetylene can't buble out of solution fast enough (it's dissolved in acetone in the bottle), so you get liquid acetone coming through the reg and the hose. Acetone attacks a lot of the materials that regulator diaphragms and hoses are made of, weakening them, possibly leading to a leak, fire or explosion.
I don't know how dangerous this is really. I have experienced acetone coming out the torch a time or two, and nothing bad happened. But that was in a busy production shop where we rebuilt our regs with new diaphragms and other parts now and then, and replaced hoses as soon as they looked worn or iffy. On the assumption that they wouldn't have this "rule" for no reason, let's assume you don't want acetone coming through the torch. If nothing else, because it screws up the flame.
But I digress! The point is, the O2 concentrator is not the bottleneck to how big a flame I can get, for the things I make anyway (mostly bicycle frames and forks).
My acetylene torch is a Smith AW1A, a small aircraft-style welding torch, not a jewelery size. If you know Smith tip sizes - I can use up to a 207 with my 5 liter per minute concentrator (5 l/m), which is my biggest tip short of a rosebud. That tip will exceed the max withdrawal rate of my #3 acetylene bottle.
With propane, which has no practical withdrawal rate limit, I can run a 'small' rosebud on the 5 l/m concentrator, and I just bought a 10 l/m concentrator that I haven't used yet. I'm almost positive I will be able to run my biggest rosebud off that.
5 l/m concentrators are far more common than 10 l/m, and the typical craigslist cost of the 10 l/m units is much higher. Roughly speaking, in Seattle anyway, you can usually find a 5 for under $200, with 10's going more like $500-800, when you can find one. It'd be cheaper to buy two 5s and daisy-chain 'em. On any given day there are several 5s for sale on Seattle CL, and zero 10s. I lucked out, bought my 10 for $75 from a guy who didn't know what he had. That's not uncommon, since they usually go up for sale because the patient died, and the heirs just want it gone. (You know these are medical devices, right? Technically you can't buy one without a prescription from your doctor, tho that is moot for buying used on CL.)
I could go on... Let me know if there's interest in more info.
