Parting / Cut-Off Time
Cut-off time from bar diameter and radial feed, with the slow-core warning.
Parting feels slow because it is: surface speed dies at the core and the last millimetre takes as long as the first ten. Many shops feed-override down near center anyway ā the calculated time is the optimistic floor.
Formula
Note: Catalog starting values only ā always confirm against your tool maker's data sheet and cut a test part. Machine rigidity, coolant and workholding shift real-world numbers.
Cut-off time from bar diameter and radial feed, with the slow-core warning. A free cnc machining: speeds, feeds & tool wear tool ā no sign-up, no upload, instant results in your browser.
About Parting / Cut-Off Time
Parting / Cut-Off Time computes the governing relationship t = ā« dr / (fĀ·n(r)), n(r) = min(1000Ā·Vc/2Ļr, n_max) live as you type. Parting feels slow because it is: surface speed dies at the core and the last millimetre takes as long as the first ten. Many shops feed-override down near center anyway ā the calculated time is the optimistic floor. 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 Parting / Cut-Off Time
- 1Enter your values ā Bar diameter, Radial feed, Surface speed, Spindle RPM cap (sensible defaults are pre-filled).
- 2Read the live results: Parting time, Mean spindle speed.
- 3Check the "with your numbers" line to see t = ā« dr / (fĀ·n(r)), n(r) = min(1000Ā·Vc/2Ļr, n_max) substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Parting / Cut-Off Time?
- āInstant, free and private ā every calculation runs client-side in your browser; nothing is uploaded
- āBuilt on the stated formula t = ā« dr / (fĀ·n(r)), n(r) = min(1000Ā·Vc/2Ļr, n_max) with authoritative sources cited on the page (Machinery's Handbook, 31st ed. ā Speeds and Feeds; Kalpakjian & Schmid, Manufacturing Engineering and Technology, 7th ed., ch. 21)
- āParting feels slow because it is: surface speed dies at the core and the last millimetre takes as long as the first ten.
- āSI ā Imperial toggle converts your inputs in place, so you can work in the units your drawings use
Frequently asked questions
What formula does the parting / cut-off time use?+
It evaluates t = ā« dr / (fĀ·n(r)), n(r) = min(1000Ā·Vc/2Ļr, n_max), exactly as published. Sources: Machinery's Handbook, 31st ed. ā Speeds and Feeds; Kalpakjian & Schmid, Manufacturing Engineering and Technology, 7th ed., ch. 21. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result ā and how far can I trust it?+
Parting feels slow because it is: surface speed dies at the core and the last millimetre takes as long as the first ten. Catalog starting values only ā 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?+
Cut-off time from bar diameter and radial feed, with the slow-core warning. A free cnc machining: speeds, feeds & tool wear tool. Many shops feed-override down near center anyway ā the calculated time is the optimistic floor. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Does it support both metric and imperial units?+
Yes ā the SI ā 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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