Welding 101

Bring a welder into your workshop for a whole new world of project possibilities

By Steve Maxwell

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Brazing is a process that uses molten bronze to join steel, cast iron and any ferrous metal without melting them. It’s similar to heavy-duty soldering, except that you need enough heat to make the underlying metal glow red while melting the bronze.

An ordinary propane torch doesn’t deliver quite enough heat for effective brazing (even on light-gauge sheet steel), but an inexpensive upgrade will get you into the game for about $70. This is what you’ll pay for a basic oxypropane torch set. Designed to be screwed onto a disposable fuel cylinder and a second tank filled with oxygen to coax maximum heat out of the combustion, this equipment delivers plenty of heat for most brazing jobs. Sets like this are available at most hardware stores.

The system comes with two simple valves connected to a torch by a pair of rubber hoses. One valve threads onto a disposable oxygen cylinder, and the other attaches to either a propane or an MAPP gas cylinder (which is liquified petroleum gas combined with methylacetylene propadiene). Although MAPP gas is more expensive than propane, it’s actually cheaper to use because MAPP develops a hotter flame, requiring less oxygen than propane. But with replacement MAPP and oxygen cylinders costing more than $10 each, the system can get expensive on anything but small jobs. You’ll get about 25 minutes of brazing time from one oxygen cylinder, and less than half of that if you have the torch cranked right up for heating metals up to 1/4″ thick. Will you be doing a lot of brazing? An oxy-acetylene cutting torch works perfectly for this operation, although there’s an even simpler option. Air-acetylene torches of the sort favoured by plumbers are the simplest way of getting plenty of heat. The best versions come with self-igniting torch heads and include a tool caddy shroud that covers the tank, offering all kinds of pockets for extra brazing rods, eye goggles, spare torch tips and marking tools.

Regardless of the heat source involved, you must always begin brazing by cleaning the metal surfaces to be joined using sandpaper, steel wool or a grinder. Parts also need to fit together with less than a 1/16″ gap, ideally under clamping pressure. Heat the metal until it’s bright cherry red, then hold the tip of the brazing rod against the joint surface. It’s possible to heat the metal too hot, causing the bronze to flare up and run off the joint without strength. If you have the temperature right, the bronze will melt within a second or two of touching with the weld area, flowing right into the joint gap and into the open pores of the metal, bonding there when it cools. Cleaning the steel beforehand is essential because dirt prevents the all-important intermingling of steel and molten bronze.

Let there be dark

The bright light created by an electric arc welder demands the use of dark-coloured eye protection, but there’s a problem. If the lens is dark enough to protect your eyes, then it’s too dark to see through until the arc is struck. And that means you’re left fumbling around blind until the welding process shows you exactly where you’re welding. At least, that was the problem until the advent of auto-darkening lenses.

Starting at about $100, you’ll find welding helmets that include a lens that darkens in milliseconds whenever bright light hits it. Tip the helmet down and the world looks like it does when you’re wearing a pair of sunglasses. But as soon as you strike an arc, the lens goes dark enough to protect your eyes. This process requires a small amount of electricity, and it’s provided by photovoltaic cells on the front of the helmet. These transform the light energy of the arc into electricity used to trigger the darkening process. Is an auto-darkening welder’s helmet a gimmick? No. Even pros who’ve mastered the skill of striking an arc blind with old-style helmets swear by auto-darkening systems.

You’ll need to protect your eyes while brazing too, although you don’t need as much darkening power to do the job. A lens that’s dark enough to protect while brazing is still light enough to let you see a bit before the metal is heated. Just don’t make the mistake of using brazing goggles while arc welding. The arc is so bright it demands a very dark lens.


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