Grinding welds on thin sheet metal without ruining the edges

GUIDE · 4 MIN READ · PUBLISHED OCT 23, 2026

A low-poly sculpture lives on its edges. The sharper the edge, the stronger the effect. A rounded edge looks like a mistake, even to someone who can't say what's wrong.

First: fix burn-through

Everyone gets burn-through on thin sheet. Close it with short pulses around the edge, pulling the hole shut bit by bit. Don't fill it from the center — a puddle in the middle makes the hole grow. Let it cool between pulses.

The goal of grinding

Remove the weld bead and level the faces so every edge reads as a crisp line. You grind the seam along the edge — never the edge itself. The edge is the form, not a defect. Don't grind it "smooth".

Coarse to fine, no skipping

Each grit should remove the scratches of the one before, not fight the metal.

1. Remove and level — 80 grit flap disc. Takes off the bead and shapes the edge. Hold the disc at a slight angle and keep moving: thin sheet heats up and burns through under an abrasive just like under an arc.
2. Finish — 120 grit. Removes the 80-grit scratches and prepares the surface for paint or polish.
3. Polish — only if you want shine and the metal allows it. Felt wheel with compound, after the full sequence.

Polishing a surface that skipped steps is pointless. The compound hides scratches but doesn't remove them, and they show up in the light.

What comes next

The finish depends on your steel: paint for mild steel, a brushed or mirror surface for stainless, nothing at all for corten. See corten vs mild steel vs stainless.

FAQ

More builder guides

• How to get a DXF laser cut (quote email included)
• Bend line UP vs DOWN: reading engraved marks
• Bend fold lines without a press brake
• Tack before you weld: panel order
• Corten vs mild steel vs stainless