Date:25 June 2014
If you’ve never welded before, today’s easy-to-use wire-feed units speed up the learning process. By Roy Berendsohn and Mike Cunningham
When you know how to weld, you can repair the rusted hand railing on your front stoep or a broken tractor hitch. You can build machines or simple workshop aids, such as heavy-duty shelf brackets. When you get good at it, you can even restore old cars. That’s a lot of applications for a single skill.
At its most basic, welding joins two pieces of metal using melted steel as the glue. Here we demonstrate that process with a flux-cored wire-feed welder. When the powdered flux inside the wire melts, it emits a gas that condenses to form a thin shell of slag. This protective layer prevents contaminants in the air from polluting the cooling molten metal and reducing the strength of the weld.
Most projects require five steps: prepare the metal; clamp the pieces in position; tack them together with blobs of metal; finish-weld the parts; clean up the assembly. Get that down and you can handle a project like the C table (see end).
Before you start
Gear up: Don’t do anything without first putting on a welding jacket or apron, leather gloves, and an auto-darkening welding helmet. Wear safety glasses when grinding – and always keep a fire extinguisher nearby.
Practise handling the gun without actually welding. Rest its barrel in one hand, and support that hand on the table. The other hand operates the gun’s trigger. Stand in a comfortable position and move the gun steadily over the work surface. Adjust your posture and gun movement so that they feel natural.
Attach the work lead to the workpiece, and hold the gun so the wire meets the weld surface at about a 30-degree angle. Touch the wire very lightly to the surface, squeeze the trigger, and gently pull the gun towards you to make your first test weld. The wire should melt off into the weld puddle at an even rate and make a steady crackling noise as you go. Adjust the welder settings if needed.
1. Prepare the metal
Mark a line with a carbide scribe or woodworker’s awl, and cut with a metal-cutting chop saw or a hacksaw. For a strong weld, clean the metal with a degreaser. Next, grind or file a slight bevel along the edges you’re welding. This ensures the weld penetrates as deeply as possible and countersinks it so you can grind it flush. Don’t overdo it or you’ll burn through the metal when you weld.
2. Position the pieces
When building a project like our C table, you’ll need to form exact 90-degree angles. Clamp the mitred surfaces together, leaving enough room to put down a tack weld. The pieces should lie flat and fit neatly without a metal burr interfering. Check the assembly’s position with a square. Use a carpenter’s aluminium triangle square on the inside of the joint, or a steel carpenter’s square on the outside.
3. Tack weld
Tack the pieces together at a couple of places along each joint. Check again for square corners; if anything shifts and puts the assembly out of square, grind away the tack weld, reposition the parts, and try again.
4. Finish weld
After you’ve tacked everything into place, lay down your final weld beads. As enjoyable as it is to create nice, smooth welds, resist the temptation to overdo it. The more metal you deposit, the more you’ll need to grind off.
5. Post-weld cleanup
Chip off the slag with a welding hammer, and then use a 36-grit grinding wheel to knock the beads down to the surrounding metal. To ensure a flat, flush surface, move the grinder along the weld, not across it. Remove any marks with a 60-grit zirconia flap disc.
Prime and paint the steel, buff some clear wax over it, or spray on a coating of clear acrylic. But do it sooner rather than later. You don’t want a layer of rust to form.
Make this metal C table
Our C table is an elegant reduction of furniture to an industrial form. Two 406 mm-square frames are joined by two 380 mm uprights. Use the structure to support a top of wood, stone, glass or metal. It’s an ideal project for a first-time welder. All 10 pieces of steel are cut from 25 mm square steel tubing with a 1,5 mm wall thickness. The pieces for the top and bottom frames are joined with 45-degree mitres. The two uprights meet the frames with butt joints. And the welding couldn’t be simpler: flux-cored arc welding with a low current setting and a slow wire speed is about as easy and forgiving a process as you can learn.
Download: Metal C table assembly
Glossary: torsional strength
The ability to withstand a twisting load before breaking. A No 9 Spax screw has a torsional strength of 5,6 N.m, whereas a typical drywall screw is rated at about 3,6.