Surface Finish Predictor — Rough Turning Steel
Theoretical Ra and Rt from feed and nose radius for rough turning steel, checked against a Ra 12.5 target.
In roughing, finish only matters enough to leave a clean skin for the finish pass. Big nose radii spread the load and survive interrupted cuts, at the price of higher radial force — back off rε on slender shafts.
Formula
Note: Catalog starting values only — always confirm against your tool maker's data sheet and cut a test part. Machine rigidity, coolant and workholding shift real-world numbers.
Theoretical Ra and Rt from feed and nose radius for rough turning steel, checked against a Ra 12.5 target. A free cnc machining: speeds, feeds & tool wear tool — no sign-up, no upload, instant results in your browser.
About Surface Finish Predictor — Rough Turning Steel
Surface Finish Predictor — Rough Turning Steel computes the governing relationship Ra ≈ f² / (32·rε) · Rt ≈ f² / (8·rε) live as you type. In roughing, finish only matters enough to leave a clean skin for the finish pass. Big nose radii spread the load and survive interrupted cuts, at the price of higher radial force — back off rε on slender shafts. Defaults are pre-filled with realistic values for this exact scenario, and the worked example substitutes your numbers step by step so the math is never a black box.
How to use Surface Finish Predictor — Rough Turning Steel
- 1Enter your values — Feed per rev f, Nose radius rε, Target Ra (sensible defaults are pre-filled).
- 2Read the live results: Theoretical Ra, Theoretical Rt, Max feed for target.
- 3Check the "with your numbers" line to see Ra ≈ f² / (32·rε) · Rt ≈ f² / (8·rε) substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Surface Finish Predictor — Rough Turning Steel?
- ✓Instant, free and private — every calculation runs client-side in your browser; nothing is uploaded
- ✓Built on the stated formula Ra ≈ f² / (32·rε) · Rt ≈ f² / (8·rε) with authoritative sources cited on the page (Machinery's Handbook, 31st ed. — Speeds and Feeds; Sandvik Coromant — Milling formulas & definitions)
- ✓In roughing, finish only matters enough to leave a clean skin for the finish pass.
- ✓SI ⇄ Imperial toggle converts your inputs in place, so you can work in the units your drawings use
Frequently asked questions
What formula does the surface finish predictor — rough turning steel use?+
It evaluates Ra ≈ f² / (32·rε) · Rt ≈ f² / (8·rε), exactly as published. Sources: Machinery's Handbook, 31st ed. — Speeds and Feeds; Sandvik Coromant — Milling formulas & definitions. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result — and how far can I trust it?+
In roughing, finish only matters enough to leave a clean skin for the finish pass. Catalog starting values only — always confirm against your tool maker's data sheet and cut a test part. Machine rigidity, coolant and workholding shift real-world numbers.
When is this calculator the right tool for the job?+
Theoretical Ra and Rt from feed and nose radius for rough turning steel, checked against a Ra 12.5 target. A free cnc machining: speeds, feeds & tool wear tool. Big nose radii spread the load and survive interrupted cuts, at the price of higher radial force — back off rε on slender shafts. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Does it support both metric and imperial units?+
Yes — the SI ⇄ Imperial toggle converts the values already in the fields, preserving the physical quantity, so you can flip mid-calculation without re-entering anything.
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