Tunnel Boring & Heavy Civil Equipment worked example

Spare Cutter Buffer with spare cutter buffer on hand of 3,000 units: a worked example

Push spare cutter buffer on hand up to 3,000 units and the picture changes. This example computes every intermediate figure at that operating point. Use it when spare cutter buffer in tunnel boring and heavy civil equipment is being sized for a buffer or safety stock review.

The inputs for this scenario

  • Spare cutter buffer on hand: 3,000 units (raised for this scenario; the documented default is 1,200)
  • Cutter consumption per day: 85 units / day (unchanged)
  • Cutter replenishment lead time: 1.1 days (unchanged)

Working through the calculation

  • Applying the documented formula (Spare cutter buffer cycle stock = spare cutter buffer daily usage × spare cutter buffer lead time) to the inputs above produces each figure below.
  • At this operating point the engine returns 32.09 days for protected days of supply, the number this scenario is built around.
  • At this operating point the engine returns 35.29 days for unprotected days.
  • At this operating point the engine returns 3,000 pieces for inventory.
  • At this operating point the engine returns 85 pieces / day for daily usage.

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 150% above the baseline at 32.09 days.
  • It divides the cutters on hand by daily consumption to give days of supply, and compares that against the replenishment lead time to show whether the buffer is protected. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • Protected days of supply: 32.09 days (headline result)
  • Unprotected days: 35.29 days
  • Inventory: 3,000 pieces
  • Daily usage: 85 pieces / day

Run it with your numbers

  • Every input above is editable in the live Spare Cutter Buffer calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.