CNC Machining worked example

Tool Life with average tool usage of 6 tools / day: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop average tool usage to 6 tools / day, then walk the calculation through step by step. Estimate cutting-tool inventory coverage from daily tool usage, replenishment lead time, and safety stock needed to protect production.

The inputs for this scenario

  • Average tool usage: 6 tools / day (the input this scenario stresses; the baseline uses 12)
  • Tool replenishment lead time: 10 days (held at the documented default)
  • Tool-life safety stock: 25 tools (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Lead-time tool demand = average tool usage × tool replenishment lead time.
  • Required cutting-tool stock works out to 85 tools at these inputs, and this is the headline figure for the scenario.
  • Lead-time tool demand works out to 60 tools at these inputs.
  • Tool-life safety stock works out to 25 tools at these inputs.
  • Tool coverage days works out to 14.17 days at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where average tool usage sits at 12 tools / day and the headline result is 145 tools, this scenario comes in 41.38% below the baseline at 85 tools.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to average tool usage, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It assumes steady average daily usage; a sudden ramp in production, a tougher material batch, or a run of premature tool failures can burn through the buffer faster than the average predicts.

Results at a glance

  • Required cutting-tool stock: 85 tools (headline result)
  • Lead-time tool demand: 60 tools
  • Tool-life safety stock: 25 tools
  • Tool coverage days: 14.17 days

Run it with your numbers

  • To rerun this with your own numbers, open the live Tool Life calculator, set average tool usage to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.