The nose radius, re, on the insert is a key factor in turning operations.
Selection of nose radius depends on the:
- Depth of cut, ap
- Feed, fn
and influences the:
- Surface finish
- Chip breaking
- Insert strength.
Small nose radius
- Ideal for small cutting depths
- Reduces vibration
- Less insert strength.
Large nose radius
- Heavy feed rates
- Large depths of cut
- Stronger edge
- Increased radial forces.
Wiper inserts should be used in high productivity applications or when high quality surfaces are required.
The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases.
The nose radius also affects the chip formation. Generally, chip breaking improves with a smaller radius.
As a general rule of thumb, the depth of cut should be greater than or equal to 2/3 of the nose radius, or 1/2 of the nose radius in the feed direction.
In turning operations, the generated surface finish will be directly influenced by the combination of nose radius and feed rate.
A conventional insert has a single nose radius, which can vary between 0.1 – 2.4 mm, and the surface finish is directly related to the feed used.
Rules of thumb for wiper inserts:
- Two times the feed = same surface finish
- Same feed – surface finish is twice as good.
The modified nose radius of the wiper inserts is within the tolerance for C- and W-style inserts, while D- and T-style have a nose configuration that deviates from corresponding conventional inserts.