Troubleshooting
Why is my mig welding undercut?
Quick answer
Undercut in mig welding usually means too much heat or too fast travel at the weld toe — the parent metal gets washed away. For this process, reduce current and slow the toe fill before touching anything else.
The specific fix
Reduce current and slow the toe fill. The general rule: reduce current, slow slightly, adjust torch angle to fill the toe.
Process checklist
- Stick-out too long — keep 8–10 mm from nozzle to work for a stable arc
- Travel too slow on thin sheet, burning holes instead of building a bead
- Wrong wire size for the job — 0.9 mm covers most hobby work in Australia