How to Extend Tool Life Despite Rising Tool Prices: Taylor's Tool Life Equation and a Minimum-Cost Calculator

Why prices keep rising

• China produces about 80% of the world's supply: of the world's mine production of 85,000 t in 2025, China accounted for 67,000 t (about 79%)^[1]
• Export licensing: in February 2025, China put exports of APT, tungsten carbide and other items under a licensing system^[3][1]
• Lead times got longer too: lead times for APT and similar shipments reportedly stretched from 4-6 weeks to 12-20 weeks^[2]

In response, major tool makers in Japan and abroad announced price revisions one after another in 2026. Among the official announcements we could confirm, the size of the increase varies widely by product category^{[4][5][6][7][8]}.

Tool cost is said to be only about 3% of the cost of one part^[18], but with increases this large, that changes. Using the equation below, you can see in numbers that when tools get expensive, it pays to lower the speed a little and use them longer.

Taylor's tool life equation: a slightly lower speed greatly extends tool life

The relationship between cutting speed V and tool life T can be expressed by the following equation, which F. W. Taylor derived from experiments about 100 years ago^[9][10].

V · Tⁿ = C

• V: cutting speed [m/min]　T: tool life [min] (cutting time until the specified wear width is reached)
• n: life exponent, determined mainly by the tool material　C: cutting speed at which tool life is 1 minute [m/min]

When you compare two speeds, you get T₂ / T₁ = (V₁ / V₂)^1/n as the ratio of the tool lives. The smaller n is, the more a change in speed affects tool life.

Lowering the speed increases the time it takes to machine each part, so the parts per corner figure does not increase as much as tool life (tool life multiplier × speed ratio). Even so, lowering the speed by 20% with carbide roughly doubles the number of parts per corner.

Don't go too lowIf the speed is too low, built-up edge (adhesion) and chatter appear and actually shorten tool life^[12][13]. Taylor's equation applies only in the range where wear progresses steadily^[10].

Calculator: what happens to tool cost if you change the speed?

Enter your current conditions and tool price, and the calculator gives tool life, parts per corner and tool cost per part at the new speed, plus the tool life and speed that give the lowest total cost including tool cost.

'Minimum-cost tool life' is the concept of economic cutting conditions presented by Gilbert in 1950^[16][17]. The higher the tool cost per corner, the longer the optimal tool life (= the lower the speed). The range between the minimum-cost speed and the maximum-productivity speed is the practical 'high-efficiency cutting zone'^[16]. n varies greatly with the tool and workpiece material, so finding n from the results (speed and tool life) of two conditions in your own shop improves the accuracy of the calculation^[9].

How to define tool life: how many mm of wear before you change the tool?

In tool life tests, tool life is defined by the width of the wear band on the flank face, VB . In ISO 3685, the international standard for turning tool life tests, a commonly used criterion for carbide is an average VB of 0.3 mm, if the wear is uniform, or a maximum VB of 0.6 mm , if it is non-uniform^[15]. However, when dimensions and surface roughness matter in finishing, the tool is changed at even smaller wear.

On the shop floor, measuring with a microscope every time is impractical, so it is common to judge by changes like the following^[11][10].

• Surface finish gets worse (gloss disappears, surface tears)
• Dimensions are drifting out of tolerance (the edge recedes as it wears)
• The sound changed or chatter appeared
• Chip shape changed (long continuous chips, color change)
• Spindle load (power) went up
• Reached the set part count or cutting time (count-based management)

For the causes and fixes of each type of wear, see the Machining Troubleshooting Encyclopedia (Flank wear / Crater wear / Built-up edge, etc.).

8 ways to extend tool life

1. Try lowering the speed by 10-20%: speed has the biggest effect on tool life. Use the calculator above to check the gain or loss including tool cost^[13][12]
2. Don't lower the feed too much: feed affects tool life less than speed does, and if it is too small the tool rubs, which increases flank wear and built-up edge. Raising the feed also raises productivity^[12]
3. Use a larger depth of cut on black scale and cast skin: a shallow cut that only rubs the hard surface layer shortens tool life^[12]
4. Direct coolant at the cutting edge: in turning, applying it from below the cutting edge removes heat more easily. For rough milling, dry cutting is the basic choice to avoid thermal cracks^[20][14]
5. Read the wear pattern and adjust the conditions: for flank wear or crater wear, lower the speed; for built-up edge, raise the speed or feed; for chipping, reduce vibration and overhang^[10][14]
6. Keep the overhang short: chatter starts to appear when the overhang exceeds 4 times the tool diameter^[19]
7. Maintain the seat and clamp: check the insert seat for wear and the shim for chips, and tighten the clamp screw to the specified torque^[13]
8. Regrind drills and end mills early: the further wear and chipping progress, the more has to be ground away. In some cases, repeated regrinding is much cheaper than buying new tools^[21]

Don't throw away used carbide; send it for recyclingUsed carbide tools can be turned back into raw material for tungsten through tool makers' and industry collection schemes^[21][22]. With prices up, it is also worth reviewing how you handle scrap.

FAQ

How should I determine n?

If you know the tool life under two different speeds in your own shop, you can find n = (log V₂ − log V₁) ÷ (log T₁ − log T₂)^[9]. Until you know, use 0.25 for carbide as a guide.

Doesn't lowering the speed lengthen machining time and cost me money?

The higher the machine and labor rate, the more it pays to raise the speed. The calculator's 'minimum-cost tool life' finds the point where machining time, tool change time and tool cost add up to the lowest total. When tools get more expensive, that point moves toward 'a little slower'.

Which should I trust, this or the tool maker's recommended conditions?

Start with the maker's recommended conditions. The equations in this article are a tool for comparing the gain or loss when you move the speed by some percentage from there.