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SESK: Stuff Everyone Should Know · sesk.info/weld-undercut-cause

Which is a common cause of undercut in a MIG weld?

Excessive voltage or traveling too fast without enough filler.

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  1. Splitting the arc evenly between both pieces
  2. Welding clean, dry metal
  3. Too much voltage or travel speed too fast ✔

Why: Undercut is a groove melted into the base metal beside the weld that never gets filled. Too much voltage, or moving so fast the wire cannot fill the melted edge, leaves the groove.

Huh, didn't know that: Aiming the arc too much at the bottom plate can also create undercut.

The dad joke
Undercut is when the weld leaves a ditch. Cut it out of your routine.
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References

Answer: Too much voltage or travel speed too fast. Undercut is a groove melted into the base metal beside the weld that never gets filled. Too much voltage, or moving so fast the wire cannot fill the melted edge, leaves the groove.

  1. Hobart Brothers, MIG Troubleshooting for Metal-Cored and Solid Wire www.hobartbrothers.com/resources/technical-articles/mig-troubleshooting-for-metal-cored-and-solid-wire
    Other common causes are excessive voltage and travel speeds that are too fast without using enough filler metal.
    Checked 2026-10-10.

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