Calculator Input
Example Data Table
Typical engineering ranges vary by material, tooling condition, machine rigidity, and inspection method.
| Process | Typical Ra (µm) | Typical Ra (µin) | Common Use |
|---|---|---|---|
| Polishing | 0.05 to 0.20 | 2.0 to 7.9 | Optical or sealing surfaces |
| Grinding | 0.20 to 1.60 | 7.9 to 63.0 | Precision shafts and bearing seats |
| Fine turning | 0.80 to 3.20 | 31.5 to 126.0 | General precision machined parts |
| Milling | 1.60 to 6.30 | 63.0 to 248.0 | Flat functional faces |
| Rough machining | 6.30 to 12.50 | 248.0 to 492.1 | Pre-finish stock removal |
Formula Used
Ra ≈ (f² / 32r) × 1000 × C
Rz ≈ 4 × Ra
Rt ≈ 8 × Ra
f ≈ √((Ra_target / 1000 × 32r) / C)
Ra = Σ|yᵢ| / n
Rq = √(Σyᵢ² / n)
Rt = Rp + Rv
Rz = average segment peak-to-valley range
1 µm = 39.3701 µin
Rz ≈ 4 × Ra
Rt ≈ 8 × Ra
Predictive equations are practical shop-floor approximations. Measured profile results depend on sampling length, cutoff choice, filter settings, and instrument calibration.
How to Use This Calculator
- Choose a mode that matches your task: prediction, profile analysis, or conversion.
- For predictive work, enter feed rate, nose radius, and adjustment factors.
- For profile analysis, paste measured heights around the mean line.
- For conversions, enter one known finish metric and the input unit.
- Press the calculate button to place results above the form.
- Review Ra, Rz, Rt, roughness grade, and process guidance.
- Use the export buttons to save the result summary as CSV or PDF.
FAQs
1. What does Ra mean?
Ra is the arithmetic average of absolute profile deviations from the mean line. It is the most common surface roughness specification for machining drawings and inspection reports.
2. When should I use measured profile mode?
Use measured profile mode when you already have profilometer readings. It is better than prediction when real production data is available and you need Ra, Rq, Rp, Rv, Rt, and estimated Rz.
3. Is the predictive formula exact?
No. It is a practical estimate based on feed marks and tool nose radius. Real results change with vibration, tool wear, insert geometry, material behavior, machine stiffness, and coolant conditions.
4. Why does the calculator show roughness grades?
Roughness grades help relate Ra values to common specification language. They provide a fast reference when comparing finishes across drawings, inspection sheets, and machining process plans.
5. Can I convert microinch to micrometers?
Yes. The conversion mode accepts Ra in microinch and returns the equivalent micrometer value. It also estimates related Rz and Rt values using common engineering approximations.
6. What is the difference between Rz and Rt?
Rz usually represents an average peak-to-valley height over multiple segments. Rt is the total height from the highest peak to the deepest valley across the full evaluation length.
7. Why do sampling length and segment count matter?
Surface texture values depend on how the profile is filtered and sampled. Different cutoffs, lengths, and segment choices can shift Rz and Rt results even when the surface looks similar.
8. Which finish is suitable for sealing surfaces?
Many sealing surfaces need a smoother finish, often around grinding or polishing quality. The correct target still depends on seal type, lubrication, pressure, material, and mating geometry.