How to weld
Practice, step by step: positions, materials, specific jobs.
Practice rather than theory. Each article is a job that beginners lose material on, taken in the order the work actually happens: fit-up, tacking, settings, sequence.
A theme runs through all of them. Most of what goes wrong on these jobs was decided before the arc was struck — a gap that should not be there, tacks in the wrong order, a sequence that lets the shrinkage add up instead of cancel. The welding itself is the easy part to fix.
- Welding thin sheet Settings and technique for 0.8 to 2 mm sheet: stitch welding, backing bars, torch angle, and why the fit-up gap ruins everything.
- Pipe welding positions How 5G differs from 6G, how the circumference is split into quarters, why 6G gives the widest qualification range, and what EN ISO 9606-1 says about a pipe test.
- Horizontal welding How to weld in the horizontal position: electrode 5–15° up, narrow beads, runs stacked from the bottom, what causes undercut and position PC to EN ISO 6947.
- Fillet weld PB The commonest shop position: electrode at 45° tilted towards the vertical leg, current 5 % below flat, a throat up to 8 mm in one run. Where overlap and undercut come from.
- Flat position PA The base every position is measured from: current at the top of the range, a 10–12 mm leg per run in the boat, twice the output. A test in PA covers PA only.
- Overhead fillet PD The T-joint above your head: current 15–20 % lower, a basic electrode, up to 6 mm per run. Where the sagging bead comes from, and why PD covers PA, PB and PD.
- Overhead welding How to weld above your head without the pool dripping: current 10–15 % lower, narrow beads, basic electrodes, neck protection and position PE to EN ISO 6947.
- Welding vertical down When a vertical-down weld is allowed and when it is not: current 10–15 % higher, electrode angle, cellulosic electrodes, overlap defects and position PG to EN ISO 6947.
- Welding a vertical weld Current, electrode angle and travel technique on a vertical: when to run uphill, when downhill, how to stop the pool sagging and which weave to use.
- Welding square tube Welding hollow section: the tacking order that controls distortion, welding the corner, and settings for 1.5 to 3 mm walls.
Frequently asked questions
Why does thin sheet burn through at the end of a seam?
Because the plate is hot by then. Settings that were right on cold metal are too much for metal that has been absorbing heat for two minutes. Either drop the current as you go, or work in short stitches with cooling time between them.
Up or down on a vertical weld?
Up for anything that carries load — the frozen bead below supports the pool, so penetration is good. Down for thin sheet and pipeline root runs, where speed matters and deep penetration would blow through.
My frames always come out out of square.
Sequence, not skill. Tack diagonally opposite corners first, check both diagonals, then weld opposite faces in turn so the shrinkage cancels. Welding face by face round the perimeter always pulls the frame towards the last weld.