What MIG does well in a small workshop

Metal inert gas welding — usually just called MIG — is the process most small workshops reach for first, and with good reason. It is fast, it is forgiving of less-than-perfect fit-up, and it puts down enough filler metal to bridge small gaps that would frustrate a stick welder. You can weld 1mm sheet one minute and 6mm plate the next with the same torch, simply by changing wire and settings.

It also suits the way small shops actually work. Short runs, awkward shapes, a bracket that needs tacking while you hold it in position with one hand — MIG copes with all of it. The main limit is that it prefers clean, dry, indoor conditions. Draughts blow the shielding gas away, and rust or paint will ruin an otherwise decent bead.

Choosing the machine, wire and gas

For general fabrication in mild steel up to about 6mm, a single-phase set with a 150–200A output will cover the vast majority of jobs. Check the duty cycle rather than the headline amperage: a machine rated 150A at 60% duty will happily run long beads at 110–120A, which is where most of your work will sit. A 13A domestic plug will limit you to roughly 130A; if you plan to weld thicker material regularly, budget for a dedicated 16A or 32A supply.

Consumables matter more than beginners expect:

• Wire: 0.6mm for body panels and thin sheet, 0.8mm as the general-purpose choice for 1mm to 5mm steel, and 0.9–1.0mm for heavier sections. Copper-coated ER70S-6 is the standard mild steel filler.
• Gas: a mix of argon with 5–15% CO2 gives the smoothest arc on thin material. Heavier plate and dirtier steel benefit from a richer 20–25% CO2 mix, which runs hotter and penetrates further.
• Contact tips: buy them by the handful in the size matching your wire. A worn tip causes erratic arcing and bird-nesting, and they cost pennies.

Gasless flux-cored wire has its place outdoors or where a cylinder is impractical, but it spatters heavily and leaves slag you must chip and brush before the next pass.

Setting up before you strike an arc

Most small MIG sets run electrode positive: the torch lead to the positive terminal and the earth clamp to negative. Check the manual, because flux-cored wire reverses this.

Then work through the mechanical basics. Fit the correct feed roller groove for your wire size, set the spool so it turns freely with a light drag, and thread the wire through the liner without kinks. Set the feed tension so the rollers grip the wire firmly but will still slip rather than crush it — too tight and the wire deforms and jams in the liner.

Set gas flow to around 10–15 litres per minute at the regulator. Screw the contact tip so it sits flush to 2mm proud of the shroud, and keep wire stick-out at roughly 10–15mm. Finally, clamp the earth directly onto bare, clean metal as close to the joint as practical. A poor earth is behind a surprising share of "the welder isn't working" complaints.

Dialling in voltage and wire speed

Voltage controls heat and bead width; wire speed controls how much filler arrives. The two must be balanced. Too little voltage for the wire speed and the wire stubs into the plate; too much and you get a flat, spattery bead with poor penetration.

Start from the chart inside the machine's side panel and then trust your ears and eyes. A correctly set weld sounds like steady frying bacon — a crisp, even crackle with no popping or stuttering. The bead should be slightly convex with fine ripples and a clean edge where it meets the parent metal.

Run test coupons on offcuts of the same thickness before touching the real job. Start at around 16–17V and 3–4 metres per minute of wire for 1mm steel with 0.8mm wire, and increase both together as thickness rises. Change one setting at a time and note what happens — that notebook will save you hours later.

Technique: angle, travel and managing distortion

Hold the torch at about 10–15 degrees from vertical, tilted in the direction of travel for a pushing technique. Pushing gives a flatter bead, better visibility and slightly less penetration; dragging gives more penetration and a narrower, higher bead. For thin sheet, push. For thicker plate on a root pass, dragging is often the better choice.

Move at a steady speed, watching the leading edge of the pool rather than the arc itself. For long seams, tack every 75–100mm first, then weld between the tacks, alternating ends to spread the heat. Thin panels will pull like a banana otherwise, and no amount of hammering will fully undo it.

Short runs and stitch welds are legitimate techniques, not cheating. For sheet metal, a series of overlapping tacks, allowing each to cool, produces less distortion than one continuous bead.

Safety, plus a quick fault-finding checklist

MIG welding produces intense UV, hot spatter and fumes. An auto-darkening helmet set to shade 10 or 11, leather gloves, a flame-resistant jacket and boots are the minimum. Never weld galvanised, painted or oil-contaminated steel without grinding it back and providing good ventilation — zinc fumes cause metal fume fever, and it is thoroughly unpleasant.

Keep a fire extinguisher within reach and stay in the workshop for at least 30 minutes after finishing, particularly if you have been welding near timber or insulation. Argon and CO2 are heavier than air and will pool in pits or low workshops, so never leave a cylinder hissing in a confined space.

When things go wrong, the cause is usually simple:

• Porosity in the bead: gas flow too low, a draught, or contaminated metal.
• Excessive spatter: voltage too low for the wire speed, or too much stick-out.
• Burn-through on thin sheet: drop to 0.6mm wire, reduce voltage, and increase travel speed.
• Wire stubbing or bird-nesting: wire speed too high, tip worn, or liner clogged.

Get the setup right, practise on scrap, and MIG will quietly become the most used tool in the shop.