MIG or TIG for 16–20 gauge sheet metal?
The answer is about heat, not process loyalty. Here's where each one wins.
The numbers first
16 ga steel is about 62 mils (0.062") — call it 1/16". By the TIG rule of thumb, that's 50–75 amps. 20 ga is half that again, 37 mils, down around 30–40 A. At these amperages the margin between "welded" and "blown-through" is a few amps and a couple of tenths of travel speed — which is why thin metal punishes sloppy settings so hard.
Where MIG wins
16–18 ga structural: ductwork, brackets, furniture frames, boxes. Short-circuit MIG with .023" wire at roughly 60–110 A is fast, forgiving, and cheap. The trade: visible spatter and a less pretty bead, and on 20 ga it becomes a race against blow-through.
Where TIG wins
20 ga and anything visible: auto body panels, stainless sinks, motorcycle tanks. TIG's foot-controlled amperage lets you feather heat exactly, fill with a bare rod, and make beads that need no cleanup. The trade: it's 3–5× slower and takes weeks of practice before your beads look like the YouTube ones.
Anti-warping playbook (either process)
| Technique | What it does |
|---|---|
| Stitch weld: 1/2" beads, skip 2" | Spreads heat input so the panel never sees sustained expansion |
| Copper backing bar | Sucks heat out of the weld zone — the single best trick under 18 ga |
| Clamp flat, leave clamped until cool | Forces the weld to shrink straight instead of banana-ing the panel |
| Lower amps, faster travel | Less total heat into the metal for the same joint |
| Planish with a hammer + dolly after | Stretches the shrunken weld zone back flat |
Settings starting points
16 ga with .023 MIG: about 70–90 A, 220–260 ipm wire speed, 75/25 gas. 20 ga with TIG: 30–45 A, 1/16" tungsten, ER70S-2 filler. Confirm both on scrap — the calculator gives you the window, the scrap gives you the number. And if your shop power comes from a generator instead of the wall, match the machine's draw at GeneratorSizer.