Educational explanation, not professional design advice. Last reviewed 24 October 2026. Disclaimer
In plain English
Every cutting edge wears as it works. Tool life is how long the edge can cut before it is too worn to give acceptable parts and has to be changed or re-sharpened. Faster cutting gets parts done sooner but wears the tool much faster, so tool life is a balance between speed and cost.
Technical definition
Tool life is the cutting time (or number of parts, or length of cut) required to reach a specified tool-life criterion. In testing to ISO 3685, typical criteria are a defined width of the flank-wear land or a defined crater depth; in production, the criterion is often surface finish, size drift, burrs or the risk of edge breakage.
How it works and where it is used
Tool wear happens by abrasion, adhesion, diffusion and chemical reactions, all of which speed up with temperature — and cutting temperature rises with cutting speed. F. W. Taylor showed that, for a given tool and work material, tool life and cutting speed follow a simple power law. Feed and depth of cut also affect tool life, but less strongly than speed.
Formula
V × Tn = C T = (C ÷ V)1/n
V = cutting speed, T = tool life (minutes of cutting), n = Taylor exponent (between 0 and 1, from tests), C = the speed that would give 1 minute of tool life. Both n and C belong to one tool, work material, feed, depth of cut and wear criterion.
Worked example
Two tool-life tests: 200 m/min gave 10 min of life and 150 m/min gave 40 min.
- n = ln(200 ÷ 150) ÷ ln(40 ÷ 10) = 0.2877 ÷ 1.3863 = 0.2075
- C = 200 × 100.2075 = 322.5 m/min
- Expected life at 175 m/min: T = (322.5 ÷ 175)1/0.2075 = 19.0 min
In the workshop and in practice
Tool life sets how often the operator or the CNC changes inserts, and how many parts an edge produces. Combined with machine rate and tool price, it determines the cutting speed that gives the lowest cost per part (or the highest output). Many CNC controls track tool life and call up a sister tool automatically.
Common mistakes and misconceptions
- Using n and C outside their test conditions. A new material, coolant or feed changes them.
- Expecting every edge to last exactly T. Tool life scatters widely; plan changes with a margin.
- Running edges to breakage. A broken insert can damage the holder and the part; change on a planned wear limit.
- Judging only by tool cost. A cheaper, slower tool can cost more per part once machine time is included.
Related calculators
- Taylor Tool Life Calculator — Tool life from cutting speed with V·Tⁿ = C, the speed for a target life, or n and C from two tests.
- Machining Cost & Tool Cost per Part Calculator — Cost per part from machine rate, cutting and handling time, tool life and tool cost per edge.
- Cutting Speed & Spindle RPM Calculator — Spindle speed from cutting speed and diameter — or cutting speed from RPM.
Related topics
- Cutting Speed — How fast the cutting edge moves across the work material, in m/min or SFM.
References
- F. W. Taylor, “On the Art of Cutting Metals”, Transactions of the ASME, 1907
- ISO 3685: Tool-life testing with single-point turning tools
- Kalpakjian and Schmid, Manufacturing Engineering and Technology (tool wear and tool life)