How to Machine Undercuts: A Practical Guide

How to Machine Undercuts: A Practical Guide

Machining undercuts demands specialized strategies, tooling, and machine capabilities. Whether you’re creating a groove for a retaining ring or a hidden clearance pocket, these steps will guide you through the process:

1. Design and Drawing Preparation

   • Specify undercut dimensions (depth, width, angle, corner radius) clearly using GD&T symbols.

   • Indicate surface finish requirements.

   • Provide a note on tool access angle or machine axis orientation if critical.

2. Tool Selection

   • For straight undercuts: choose L-shaped or bull-nose undercut cutters with rigid shanks.

   • For angle undercuts: use dovetail or form-profile tools.

   • For internal undercuts on a lathe: live tooling with angular holders or slidetrueing tools.

3. Machine Capability Assessment

   • Confirm access: 3-axis vs. 3+2 vs. full 5-axis milling.

   • Ensure sufficient clearance for tool tilt and holder.

   • Verify through-tool coolant availability for chip evacuation.

4. CAM Programming

   • Define clearance and retract planes to avoid collision.

   • Set multi-axis tool orientation: tilt angle, axis rotation limits.

   • Break the undercut into multiple shallow passes to reduce tool deflection.

   • Simulate the full toolpath in CAM software, checking for gouges or collisions.

5. Cutting Parameters

   • Use conservative depths of cut and light radial engagement.

   • Increase spindle speed to compensate for small cutter diameters.

   • Maintain proper chip load to avoid rubbing and heat buildup.

6. Chip Control

   • Employ high-pressure coolant or air to clear the recess.

   • Program cyclic retractions to shake loose chips.

   • Polish flute surfaces on carbide cutters to reduce chip adhesion.

7. Fixturing and Workholding

   • Ensure stable clamping to counteract cutting forces.

   • For deep undercuts, consider angle plates or vacuum fixtures to maximize access.

8. Inspection and Quality Assurance

   • Use bore scopes, air gauges, or CMM probes to measure hidden features.

   • Verify undercut depth, width, and surface finish against drawing callouts.

   • Document results in an inspection report for traceability.

By following this structured approach, machinists can reliably produce undercuts that meet tight tolerances and surface requirements. Each step—from design clarity to final inspection—plays a pivotal role in successful undercut machining.