Overview
I'm posting this to try to save you guys a little time and money if you ever find that you need to join two bits of aluminum (or brass or galvanized steel) together and bolts, rivets, glue, JB weld, etc. doesn't quite suit your needs. Some features of this is that it can produce a nice, clean finish and a very strong joint. It is also a lot easier than welding. I've never welded anything in my life and the professionals agree that welding aluminum is difficult, so I skipped that option altogether.
What I'm going to cover here is the use of a specifc type of brazing rod called DuraFix. I don't want to be a shill, but after trying some nickel-silver brazing rod, this was easier and produced better results and supposedly doesn't produce toxic fumes. With regular brazing materials, you'll also need to apply flux to the parts and heat up your components without burning the flux or melting the parts, yet still getting it hot enough for the brazing rod to flow. The first brazing rod I tried had a melting point around 1100 F if I recall correctly. Durafix melts at 732F.
Supplies:
All available at your local home improvement store.
A vise, c-clamp or fire-bricks to hold your workpiece. (regular bricks or concrete can explode if they reach the temperatures that you might achieve in brazing).
Welding goggles/mask number 3 to 5 shade level
Gloves (heat resistant welding gloves are best, but mine are just leather)
Stainless steel bristle brush (it's crucial to use SS bristles)
Mapp gas torch
bucket-o-water
Special purchase
Brazing rod (http://durafix.com/) They have an instructional video there as well.
Safety
Do this in a well ventilated area. Don't huff the fumes.
Burning Mapp gas produces harmful UV light, so wear appropriate protection. Sunglasses are not appropriate. If you decide to ignore this, at least try to limit direct line of sight to the flame and look out for sore or itchy eyes. Stop - it's the UV causing that.
Do your brazing in a clean area without flammable materials around. You want to be able to immediately set down your still hot, turned-off torch if problems arise. No sparks will fly, but an occasional drop of melted rod can drop off your workpiece.
The goods
Here is my setup. The torch in this picture is not the one that I currently use. This one is a fuel and oxygen torch. It is hot enough for some welding, has a tiny tip and uses up the oxygen very fast. This is not the best workspace. Having a bench and a larger area would be nice. It's cramped because it is on my apartment balcony.
To keep from burning the whole building down, I have this close by.
Here is my current torch. It can use Mapp or propane and has no second valve for oxygen. Plain air is sucked into the openings in the middle of the tip. Bernzomatic has a table describing temperatures of the various gases but it boils down to propane is hot, Mapp is hotter, acetylene is hotter still, and all of them are a good bit hotter combined with an oxygen feed. If you go the oxygen route, I suggest getting a real tank at a local welding supply. Under normal temperatures, oxygen doesn't like to go to a liquid state, so you're only getting a few ounces of compressed O2 in the little cylinders at Home Depot. Mine lasted about 15 minutes during my first test runs. When using this torch to heat anything bigger than an couple ounces of aluminum, turn it up full blast and hold the tip about an inch away from your material. If the handle gets hot, take a break to let it cool down. You don't want the gas to ignite prematurely. I haven't done this yet, but it would probably take at least 20 minutes at full-blast to become a risk. Also keep the head of the tank elevated so that liquid fuel doesn't flow into the line and out the torch.
I initially tried using one of the fist-sized, mini butane torches as suggested by some tutorials on the internet and although it can reach high temperatures, it doesn't put out enough heat to work with anything larger than a few coins.
Aluminum is soft, so to protect my workpieces while they're clamped, I use some angle aluminum bits inside the jaws of the vise or c-clamp or locking pliers so that no steel ever touches the soft aluminum. Make sure they're free of burrs too. I'm going to cut some larger ones without the holes to exert less pressure with a smoother surface as the workpiece can become a little soft without melting when heated up to working temps.
As we all know, aluminum is an excellent heat conductor. So you should have as little contact with the workpiece as possible while still holding it securely. On this piece, I've brazed the tube on top to the rectangular base by putting the brazing rod inside the tube. The clamp that you see can hold it securely and still offer relatively little mass to transmit the heat to the giant black heatsink on the left. Holding your workpieces together is crucial as well. Rubbing the brazing rod all over the pieces will knock them around without being secured. For this piece, I had some snug washers to slip around the tube and another c-clamp and locking pliers to hold those down in position on the rectangular base.
The actual process of brazing is best demonstrated by the video on the durafix website. I'll only add that my Mapp gas torch heats the workpieces maybe five-times slower than what you see in the video. I'm also still not as good at getting the rod to flow smoothly.
Here is a nearly finished part. I still have some more finishing to do, but you can see it is fairly smooth. This is about the 5th joint I've brazed in my life and it came out quite well. That clevis sticking out is held in quite securely. If I tried to rip it out, the aluminum would probably tear before the joint would fail. The brazing material is also harder than aluminum, so care should be taken when you file or sand it down to keep everything smooth and flush. To get that finish, I swiped away excess brazing material with a wet, folded paper towel while it was still melted. Then I filed the joint down with a small hand file, then I used some 200 grit sandpaper, then some abrasive pads for the current finish.
These tips, along with the demo video, should be enough to get you safely started on brazing your own joints.
