Why Thin Gauge Changes Everything

Sheet metal work lives or dies on heat control. On a 6mm plate you can lean into the amps, run a fat electrode and let the weld cool at its own pace. Do the same on 1.2mm mild steel and you have punched a hole before you finish your first dab. Thin gauge gives you a narrow window between "not fused" and "blown through", and MIG and TIG sit at different points in that window. MIG gives you speed and forgiveness; TIG gives you control and presentation. Neither is better in the abstract — it depends entirely on the job in front of you.

MIG: The Workhorse for Sheet Metal

Metal inert gas welding — MAG, strictly speaking, when you are running a CO2 mix on steel — is the default choice for most fabrication. A continuous wire feed means you can run long seams without stopping to add filler, and the process tolerates gaps, slightly grubby metal and a shaky hand far better than TIG.

For body panels and light fabrication, 0.6mm and 0.8mm wire are the sweet spots. A 0.8mm wire on 1.0–2.0mm steel with a 75/25 argon-CO2 mix is hard to beat for speed. Drop to 0.6mm when you are into 0.8–1.0mm panels, particularly on automotive work where distortion is the enemy.

Settings matter more than badge on the machine. As a rough starting point for 1.2mm mild steel, try around 40–60 amps with wire speed dialled until you hear a steady bacon-frying sizzle rather than a crackle or a hiss. Keep the torch angled about 10–15 degrees from vertical, push rather than drag, and keep your stick-out short. Short, overlapping tacks — back-stepping as you go — will beat a continuous run on panels every time. If your set has a stitch or pulse function, use it. If not, your trigger finger does the same job for free.

TIG: Precision and Presentation

Tungsten inert gas welding is slower, fussier and needs two hands and a foot, but it produces the tidiest beads you will get on thin sheet. For steel and stainless, run DC electrode negative with pure argon and a 1.6mm 2% lanthanated tungsten. For aluminium, switch to AC, ball the tungsten slightly and expect to spend real time learning the pedal.

On 1mm stainless you might be running 30–45 amps; 1.5mm mild steel sits around 55–75 amps. You control the heat with your foot and the filler with your free hand, which means you can ease off at the edge of a panel instead of blowing it open. TIG also lets you fuse edges with no filler at all, which is invaluable for butt joints on visible work.

The trade-off is speed. Expect TIG to take two to three times as long as MIG on the same joint, and expect to be far more disciplined about cleanliness. Any oil, mill scale or paint will show up instantly in the weld.

Head to Head on Thickness and Finish

• Best thickness range: MIG shines from about 0.8mm upward; TIG is comfortable from roughly 0.5mm to 3mm and beyond.
• Heat input and distortion: TIG is more controllable, so panels stay flatter. MIG puts in heat fast, so tack-and-cool technique is essential.
• Finish: TIG beads are clean, stack-of-dimes neat and often need little dressing. MIG beads are functional and usually get ground back.
• Speed: MIG wins comfortably — often three to four times faster on long seams.
• Equipment cost: A usable 150–200A MIG set is cheaper than a comparable AC/DC TIG, and much cheaper once you add a bottle, regulator and pedal.
• Skill ceiling: MIG is quicker to learn to a serviceable standard. TIG rewards patience but takes months, not evenings, to master.

Matching the Process to the Job

For classic car restoration, patch panels, sills and floor repairs, MIG with 0.6mm wire and a good supply of clamps is the sensible default. You want speed, you want to keep heat local, and most of it gets dressed back anyway.

For stainless kitchen work, brewery fittings, visible architectural metalwork, bike frames, or any job where the weld is on show, TIG justifies the extra time. It is also the better choice for thin aluminium, where MIG demands a spool gun or a push-pull setup and still tends to run hot.

Plenty of workshops keep both. A 200A MIG for the bulk of the work and a 200A AC/DC TIG for the fiddly, visible and exotic jobs is the classic two-machine setup, and it covers almost everything a small fabrication shop will see.

Setting Up Well Matters More Than the Process

Whichever route you take, the fundamentals decide the result. Clean the metal back to bright steel with a flap disc or Scotch-Brite, degrease with a proper panel wipe, and take the time to get your fit-up tight — gaps are what force you to pour in heat. Clamp or tack the work to a copper or aluminium backing bar where you can; it pulls heat away and stops the edge from dropping.

Check your gas flow rather than guessing: around 10–14 litres per minute for MIG, 8–10 for TIG, and always with the correct shroud or cup in good condition. On a 13A plug you are realistically limited to about 130–150A of output, so for anything heavier plan a 16A supply or a dedicated welding circuit.

Finally, buy offcuts and practise. Ten minutes of running beads on scrap 1.2mm sheet will teach you more about your machine than any manual. Get the sound and the puddle behaviour locked into memory, and both processes become tools you reach for deliberately rather than by habit.