Ask your WELDING questions here.

Pretty sure you'll need hydrogen, not acetylene, to weld aluminum. No idea if you can get away with the acet instead though.

accet. isn't one of the cleanest burning fuel gasses, and just as soon as I say it probably won't work, somebody will come along and say "Oh ya we use accet. all the time to weld alum." but i've never seen alum welded with accet.
i've never heard of using hydrogen for a fuel gas.
propane does burn clean and i've seen it used in welding irrigation pipe in the field.

My grandma used oxy-hydrogen for welding aluminum airplane fuel tanks in WWII. Thats pretty much the extent of my knowledge on the subject.

Propane is a naturaly occuring gas in petroleum and during WW2 I would imagine everything petroleum related was converted to fuel for whatever. Thus the reason for hydrogen as a fuel gas. I'm not sure you can even get it from the welding supply. Just for ? I ask'em tomorrow.

You should be able to. I've heard of both O-A and O-H welding aluminum in modern times. Hydrogen is cheaper, I think, but not quite as hot and harder to see the flame. If you google O-A welding aluminum you should get plenty of links- mainly for sheet metal and small parts though. You'll need a big tank and big tips to weld anything the thickness of a fork leg- the idea is to weld it before the whole thing turns into a blob.

I tried to be polite.

If you have to ask if your mig welder will do the job, then you do not have the knowledge or skill to do the job.

IF you do get the tab welded on properly and in the exact right place it will distort the fork tube.

Then when you are flying down the road with a passenger on, think about that welded on tab to your cast fork.

Will it hold at a XX mph panic stop?

Tig is the way to go for a job like that, it will still distort the fork tube. I was welding 1/4 " aluminum yesterday using a TA185. (185 amps ac) Its not big enough, so I have to use helium/argon mix to get a hotter arc. Like said above, the weld needs to be done before it turns into a big mess.

A spool gun on DC is the other possibility, but its such a short weld that the cold start will make it difficult.

The original is a one piece cast part for a reason. I am a welder and I bought the fork legs.

Some good news. Like I said in an earlier post, I converted my /6 to twin disc brakes.

3 years ago me an my adult daughter were going through the twisties in the swamps with my brother riding along
on his Valkrie. A deer ran out in front of us. I had enough front brake to squeal the front tire. Impressed me for the old /6. We missed the deer.

The conversion is worth it, I just would not do it with a welder.

Best of luck
David

I am a medicore welder at best. I have welded aluminum successfully with oxy acetylene. I have used the Henrob/Cobra type torch, although torch type isn't especially critical. It does help to get ther pressure down so you don't blow the puddle all over the place. The bigest limit to gas welding aluminum is operator skill, it take a touch to keep the heat just right.

This guy is the "savant" of gas welding aluminum. https://www.tinmantech.com/index.php

When my buddy bought the Henrob torch at the flea market at Mid-Ohio, I though oh yea, there is always have one of those "savants" at events that seems to be able to weld anything with anything. We set up the torch, I watched the DVD and I tried it. My two coupons stuck together. They weren't perfect, but they stuck.

Even with a month of practice I would consider trying to weld that fork leg.

Eric

I am not even going to pretend to be a welder. I'm just trying to bend something back into shape. The crash bar on my KTM 950 was bent on a get-off last year. I have removed the crash bar and would like to bend the lower mount so that the upper part of the bar is not touching the gas tank. I have a propane torch. Will this generate enough heat to bend the crash bar?
TIA

Same here, just sheet metal, plate and castings. I was taught to put some pure acet soot over it, and when that burns off you are pretty close to welding temp. Not pretty, but oxy/acet welding of aluminium was common before fancy welding equipment became readily available. I have a Henrob too, I have stuck 2 Coke cans together to try and duplicate the demos I saw, but haven't tried it on any alloy....maybe I should give it a go.

For those interested in oxy-acetylene welding, here is an archived book from 1919: http://archive.org/details/oxyacetylenewel01campgoog
and another from 1916: http://www.craftsmanspace.com/free-books/oxy-acetylene-welding.html

The definitive oxy-acetylene welding book was published by Linde/Union Carbide titled "The oxy-acetylene handbook". I have a couple of used copies found on ebay and Amazon. Modern books on oxy-acetylene welding are not easy to find.

I have a fondness of reading how to do things and appreciate the benefits of reading about others mistakes. Mistakes still happen, just not the same ones. The definition of an expert is someone who has made all the mistakes possible and can immediately recognize when one has been started.

A couple of things I intend to try are the wet sock trick to stop heat and making a backing/support piece from sheet steel. The wet sock is stuffed in the fork tube (and maybe a wet rag around it as well) to keep it cool. The backing plate holds the tang in place and prevents dripping molten aluminum while welding. With enough skill, this should work.

No one else answered, so.

When I straigtened my crash bars we used an oxy kit, because that's what was available - but you only need/want the metal just turning red anyway so we weren't putting in a lot of heat in compared to what oxy can put out.

My guess is that provided you have no draughts you'll do it. Maybe get some steel tube from a junk yard and practice with that first ?.

To be honest the biggest problems were getting enough leverage and not twisting the bars so the mounts didn't fit any more - ideally have the mounts bolted down to something really solid and use a long lever or hydraulics to straighen the bars. Took a lot more force than I expected to straighten mine.

Pete

+1

Don't mess around with brake stuff.

Please post up pics while you are doing this and some pics of the finished repair..

I have been a fabricator for 36+ yrs and wouldn't attempt this the way you are...but then again, I have Experience and a few nice welders...good luck and carry on. (Several others have tried to explain why they wouldn't trust the repair as you are going to do it, add me to that list).

I wish I had the written verbal skills of Benesesso and could explain all the pitfalls that await, however I am a man of limited vocabulary skills...so I just say....After you atr done experimenting and Learning...do yourself a favor......Buy a new fork leg.

In my not so humble opinion gas welding a cast aluminum part requiring structural integrity would be sketchy at best. I've seen gas welding done on a lot on aluminum race car bodies, never seen it attempted on a cast structural member. Wouldn't porosity be a major issue?

Here is what I meant by a backing plate:


This was cut from 24 ga galvanized steel. The galvanizing needs to be etched off before heating, but that's the idea.
I also plan to remove that bit of rubber by the upper tang in the caliper pin hole.

Also, to reiterate, this lower tang has no load. It's the upper tang that takes a reaction force from the brake pad.

Edit: the notion is that this tang, cantilevered off the caliper support, takes the rotating force from the the disc as the brakes are applied. After looking at this bit of cast aluminum, I am not so sure that makes sense. The pad is steel but the aluminum is not gouged from the pad contact. Instead, I am thinking the pin on the back of the pad that fits into a hole in the piston transfers the pad force back into the caliper body. Otherwise, the aluminum would wear away as the steel pad rubs when the brakes are applied.

Yes, along with messing with the heat treat condition of the part, depending upon the aluminum alloy.

I'd at least get a MAP gas canister, burns hotter than propane, have successfully bent 1/2" tubing that way. If somehow that is not enough heat two torches might do the trick. BTW, recently bought a torch extension hose for $20 and it makes work much easier, you can hang the gas canister somewhere (it comes w/ a ring and hook) and the torch is waaay less awkward to handle w/o the canister attached

It looks like yer gonna cast aluminum to the fork leg. If welded properly you shouldn't need the backer at all.

both pieces beveled. Weld one side
Back grind the other side and weld. A full Penetration weld. Tig or spoolgun.

you should know what the fork is made of to know what filler to use

If I remember right, the pads are stopped in the caliper and the caliper has a nylon button that keeps the caliper from spinning. I will look, my bike is in the garage.

On cast aluminum, I usually weld it with a tig torch.

As part of the preparation, I make the first pass over the parts with the tig torch and no filler.
This will cook the junk out of the cast and float it to the top. It also adds some preheat. I then clean up again for the real weld.

I have seen a few make a first pass with filler and grind it all out because the junk in the cast.
They then start over and make a pass with filler for a weld that is cleaner.

Just a note, I only use wheels made for aluminum because most wheels made for metal are made of aluminum oxide. Exactly what I DON'T want in my welds.

My old welding helmet is an ESAB bought by my dad back when auto helmets were pretty space age stuff, it's getting a bit flaky in the switching, I'll have a look at replacing the battery but am looking at getting a new one. What do I look for in the budget/med $ offerings? Adjustable shade & sensitivity obviously, big lens,anything else?

Cheers
Clint