Tunnel Boring & Heavy Civil Equipment worked example

Spare Cutter Buffer with spare cutter buffer on hand of 600 units: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop spare cutter buffer on hand to 600 units, then walk the calculation through step by step. Estimate spare cutter buffer for tunnel boring and heavy civil equipment using production-ready inputs so teams can plan replenishment and safety stock using actual usage and lead time.

The inputs for this scenario

  • Spare cutter buffer on hand: 600 units (the input this scenario stresses; the baseline uses 1,200)
  • Cutter consumption per day: 85 units / day (held at the documented default)
  • Cutter replenishment lead time: 1.1 days (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Spare cutter buffer cycle stock = spare cutter buffer daily usage × spare cutter buffer lead time.
  • Protected days of supply works out to 6.42 days at these inputs, and this is the headline figure for the scenario.
  • Unprotected days works out to 7.06 days at these inputs.
  • Inventory works out to 600 pieces at these inputs.
  • Daily usage works out to 85 pieces / day at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where spare cutter buffer on hand sits at 1,200 units and the headline result is 12.83 days, this scenario comes in 50% below the baseline at 6.42 days.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to spare cutter buffer on hand, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It assumes a steady daily consumption, but cutter wear is highly ground-dependent — a mixed-face or boulder-laden reach can spike usage well above the average and burn the buffer faster than the model predicts.

Results at a glance

  • Protected days of supply: 6.42 days (headline result)
  • Unprotected days: 7.06 days
  • Inventory: 600 pieces
  • Daily usage: 85 pieces / day

Run it with your numbers

  • To rerun this with your own numbers, open the live Spare Cutter Buffer calculator, set spare cutter buffer on hand to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.