Turning Surface Roughness Calculator
Estimate the ideal theoretical turning surface roughness Ra and peak-to-valley cusp height from feed per revolution and tool nose radius.
Results use the inputs above; example values are illustrative and are not tool-specific speed/feed recommendations.
Formulas and Calculation Method
Ra ≈ 1000 f² / (32 r) µm; Rt ≈ 1000 f² / (8 r) µm; ideal target feed ≈ sqrt(32 r Ra / 1000).
Theoretical turned finish improves with a smaller feed per revolution or a larger tool nose radius. The commonly used ideal geometric model gives Ra approximately f²/(32r), with consistent length units. The exact circle-based maximum cusp height is r − sqrt(r²−f²/4). The inverse result is a theoretical feed value to compare with actual machine and tool constraints.
Important Assumptions and Limitations
Not a prediction of measured Ra or a substitute for surface inspection. Insert wiper geometry, chatter, built-up edge, machine rigidity, workpiece material and edge preparation affect measured finish. Use the inverse result only as a first-pass geometric estimate.
Frequently Asked Questions
Will the actual Ra match this result?
Not necessarily. This calculator estimates the feed-mark geometry under ideal stable conditions.
Can I keep increasing corner radius to improve finish?
An excessively large nose radius may raise cutting forces or chatter; assess the whole setup.
Need the Right Cutting Tool?
Match this calculation to your workpiece material, machine setup and required tooling dimensions. Explore ONMY tools or share your application for a quotation.
Explore Turning ToolsRequest a QuoteTechnical references: Machining Doctor — Turning Calculators. Calculations are independently implemented for ONMY; source links do not imply endorsement.
