How big a brazing torch do I need?

[Chris Green]

I know this is a bit of a 'how long is a piece of string' question but I need some sort of way of working out what gas brazing torch I need to do something.

I want to fix a small crack in a transaxle casing from a mower, the casing is maybe 8" in diameter and made of 1/8" thick (or a little thicker) aluminium.

I have a "laser 4707" aluminium brazing kit and my trial on a bit of

1/8" thick aluminium angle worked pretty well (I'm used to soldering and welding so something sort of half-way wasn't too difficult). I did that with a Bernzomatic TS2000 torch which I bought a long while ago for odd plumbing jobs.

However the Bernzomatic TS2000 won't get the transaxle casing hot enough, it's fairly close but not enough to get the material to 'tin' nicely.

So, would a bigger/better torch which uses the same gas canisters as the TS2000 be enough. The Bernzomatic site seems to suggest that the TS4000 (which Screwfix sell -

quite a lot beefier than the TS2000 and it can use the MAPP gas bottles which are also hotter I believe.

[newshound]

Still looks a bit small to me, although I agree that MAPP will give you some more "oomph".

My "big" propane torch has a nozzle about an inch in diameter and I suspect that this might struggle with your transaxle. I'm making the assumption here that aluminium casting alloys "suck" heat away faster than iron or steel.

My other "secret weapon" for brazing ferrous or cuprous bits is a selection of vermiculite "fire bricks" as sold for solid fuel stoves, with these you can build some containment and reflection for many shapes (although a transaxle is probably quite difficult).

I do have the cheap Lidl inverter welder, if I had your problem I might be tempted to get a TIG torch for it.

[Chris Green]

I have an inverter welder too, and a MIG, but the crack I'm mending looks a real candidate for brazing as one is much less likely to melt the surroundings.

[John Rumm]

IIUC you need an inverter than can do AC output to be able to successfully TIG ali.

(although you could use ali wire in MIG machine with pure argon - although you either need a good wire feed and a PTFE liner for the torch lead, or a add on spool gun)

[Brian Gaff]

It kind of makes me think if its a one off job you might find some engineering company that would do it for you at a reasonable cost. Brian

[Chris Green]

Yes, as I said I do have a little inverter welder *and* a MIG welder but looking at the extras needed (and skills probably) to use them on aluminium I decided that brazing was the way to go.

Also, as it's a repair of a crack, *not* having to melt the aluminium itself is a big plus for brazing. I don't even need it to be particularly strong, just oil proof.

[Chris Green]

If my (relatively) cheap aluminium brazing doesn't work then that's exactly what I'll do. Having the ability to braze aluminium and other non-ferrous metals would actually be very handy around the place so it will probably become more than a 'one off'.

[tabbypurr]

Sounds like all you need is a £2.50 Chinese torch. Point them both at the workpiece.

NT

[Dave Plowman (News)]

I've done some basic ally welding with a domestic MIG. I needed a boss in a bit of 3" diameter tube for a sensor. Didn't need any extras - simply a reel of ally wire and an argon cylinder. You might need to pre-heat something that large with a gas torch, though.

[newshound]

Don't think so, TIG is basically DC, normally with the opposite polarity to MMA (stick) welding. Professional TIG welders have a high frequency AC for striking the arc, without that you have to scratch-start.

You can't TIG with a "transformer" stick welder, you need the better constant current supply of an inverter.

[Chris Green]

Well, I bought one of these, partly because it was cheap, partly because it coud be delivered on Sunday (it was) and partly because the reviews seemed mostly OK.

... and it's *excellent*. It's way hotter than my Bernzomatic TS2000 and did the job I needed on my transaxle with no problems. I'd also recommend the "laser 4707" aluminium brazing kit, I found it really quite easy to braze neatly over the crack.

[newshound]

That's good to know. Added to my Amazon wish list for future reference

[John Rumm]

You can get basic TIG DC machines (some with HF start as well), but you can also get AC/DC TIG. I tend to see people doing TIG on ali using AC machines since you get a cleaning effect every half cycle - not just because they have HF start.

E.g. decent DC TIG with HF start:

cf, higher end machine with AC as well:

[newshound]

Thanks, didn't realise that. I'd only ever looked at lower end TIG.