Stick Welding Undercut Troubleshooting
Undercut in stick welding appears as a groove melted into the base metal along the weld toe that is not filled properly by weld metal. It is commonly caused by excessive amperage, incorrect rod angle, excessive travel speed, poor weave control, or improper electrode manipulation. Undercut weakens weld strength, creates stress concentration points, and can cause weld rejection on structural and code work.
Common Symptoms
- Visible groove along the weld toe.
- Sharp edge transitions beside the weld bead.
- Weld bead appears narrow or rope-like.
- Undercut worsens near restarts or weave edges.
- Grinding reveals reduced weld toe thickness.
- Excessive spatter and aggressive arc behavior.
Likely Causes
- Amperage too high: Excess heat melts the base metal faster than filler metal can refill the edges.
- Travel speed too fast: Rapid movement prevents the puddle from filling the weld toes completely.
- Incorrect rod angle: Excessive drag or push angle concentrates heat on one edge.
- Excessive weave width: Wide weaving cools the puddle unevenly and leaves the edges underfilled.
- Arc length too long: Long arcs create unstable puddles and aggressive sidewall washout.
- Poor pause timing: Insufficient pause at weave edges prevents toe fill.
Inspection Steps
- Inspect both weld toes for grooves or sharp edge transitions.
- Verify amperage settings match the electrode size and position.
- Check rod angle during welding.
- Review travel speed and weave width.
- Inspect restarts for localized undercut.
- Inspect work clamp connection and arc stability.
- Verify electrode condition and storage.
Visual Wear Indicators
- Sharp grooves along weld edges.
- Thin weld toes.
- Overly convex or narrow bead profile.
- Irregular weave spacing.
- Excessive sidewall washout.
Common Wrong-Part Mistakes
- Using oversized electrodes on thin material.
- Running low-hydrogen rods at excessive amperage.
- Using the wrong polarity for the electrode type.
- Trying to cover undercut with additional cold passes instead of grinding and repairing properly.
Field Fix vs Proper Fix
Field fix: Lower amperage slightly, shorten arc length, slow travel speed, and pause briefly at weave edges. Proper fix: Grind out severe undercut, correct the welding procedure, improve rod manipulation technique, and match electrode size to the joint geometry and material thickness.
Related Failure Paths
- Slag inclusion
- Lack of fusion
- Toe cracking
- Porosity
- Cold lap
Safety Notes
Grinding out undercut creates sparks, debris, and airborne particles. Use proper eye protection, gloves, hearing protection, and ventilation during weld repair and cleanup operations.
Sources Checked
- Lincoln consumables catalogs
- Lincoln welding equipment references
- Uploaded welding safety and consumable references
