01 / METHOD
How to use this calculator
- Select metric or inch dimensions.
- Enter insert nose radius and feed per revolution in the same unit.
- Calculate theoretical Ra and Rt.
02 / APPLICATION
Where it helps
- Comparing finishing feeds
- Checking whether a programmed feed is geometrically plausible
- Evaluating nose-radius changes
03 / BOUNDARIES
Assumptions and limitations
Assumes
- Ideal round nose profile
- Stable continuous turning
- Feed marks dominate the surface
Does not cover
- Actual profilometer values can differ greatly
- Does not include vibration, wear, or built-up edge
- Not a bearing-area or waviness model
04 / QUESTIONS
Frequently asked questions
Why is actual Ra worse than calculated?
Vibration, machine condition, material tearing, built-up edge, insert wear, edge preparation, speed, and measurement settings can dominate feed geometry.
Can a larger nose radius always improve finish?
The formula predicts lower geometric roughness, but a larger radius raises cutting forces and may cause chatter or deflection in a light setup.
Are Ra and Rt interchangeable?
No. They describe different profile characteristics. This calculator estimates both from the same ideal feed-mark geometry.