Choosing the correct nose radius for grooving comes down to drawing requirements, groove depth, rigidity, and material. Follow this straightforward logic:

1. Check the required corner radius on the print: The nose radius of the insert must not be larger than the corner radius specified in the groove.
◦ If the drawing calls for a small radius, use a small nose radius.
◦ If no strict radius is required, choose a larger one for longer tool life.

2. Consider the depth of the groove
◦ For shallow grooves: use a small radius to avoid chatter and ensure clean cutting.
◦ For deep grooves: use a larger radius for stronger cutting edges that resist chipping.

3. Evaluate machine and workpiece rigidity
◦ For slender shafts, thin walls, or weak setups: use a small radius to reduce radial force and minimize vibration.
◦ For rigid machines and solid workpieces: use a larger radius to allow higher feeds and better tool life.

4. Match the material
◦ For steel, hard materials, or materials prone to chipping: use a larger radius for better strength and wear resistance.
◦ For soft, sticky materials like aluminum or copper: use a small radius to improve chip breaking and prevent chip wrapping.

5. Consider surface finish
◦ For a smooth surface finish: use a small radius with lower feed rates.
◦ For general-purpose machining: use a larger radius for higher productivity.

Simple rule of thumb
• Use the largest possible radius that fits the groove and avoids vibration—it will last longer and be more stable.
• Use a smaller radius when you need fine finish, have shallow grooves, weak rigidity, or struggle with chatter.