How do you size a spare cutter buffer for a TBM?

Divide cutters on hand by daily consumption to get days of supply, then check it against replenishment lead time. Here 1,200 cutters at roughly the modeled usage give about 12.83 protected days of supply.

What is a good days-of-supply for TBM cutters?

Enough to comfortably exceed your replenishment lead time with margin for a wear spike. In this example the protected days of supply is 12.83 days against an unprotected figure of 14.12 days — the difference is the cushion the buffer provides beyond raw consumption.

Why does cutter consumption vary so much?

Cutter life depends on ground abrasivity, face pressure, boulders, and rpm. Hard, abrasive rock or a mixed face can multiply wear rates several times over the design assumption, which is exactly why a steady-average buffer needs headroom.

What happens if I run out of spare cutters?

You either stop the machine and wait for a shipment — burning ring-build and standby cost — or launch an unplanned intervention to swap tools, both of which cost far more than carrying a larger buffer. That asymmetry is why cutter stockouts are treated as a serious schedule risk.

Cycle stock vs safety stock for cutters — what's the difference?

Cycle stock is the routine quantity you expect to consume over a replenishment cycle. Safety stock is the extra held specifically to absorb wear spikes and lead-time slips. Both feed the total buffer, but only safety stock protects you when the ground turns nasty.

How do I know when to reorder cutters?

Reorder when your remaining days of supply drops to your replenishment lead time plus a safety margin. If your buffer covers 12.83 protected days and the shipment takes most of that, you're too tight and should raise the on-hand quantity or expedite.

Tunnel Boring & Heavy Civil Equipment calculator

Spare Cutter Buffer Calculator

Spare cutter buffer sizing tells you how many days of continuous tunneling your on-hand stock of disc cutters and cutting tools will cover, and whether that buffer clears the replenishment lead time. On a TBM drive, cutter wear is the pacing consumable — abrasive or blocky ground can chew through discs far faster than plan, and running out means either an unplanned hyperbaric intervention or a stopped machine, both catastrophically expensive. Tunnel superintendents and procurement leads use this to set reorder points so a cutter shipment always lands before the shelf empties. The calculator converts your on-hand quantity, daily consumption, and supplier lead time into protected days of supply so you can see your safety margin at a glance.

What this calculator does

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.
Use it when spare cutter buffer in tunnel boring and heavy civil equipment is being sized for a buffer or safety stock review.
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.

Formula used

Spare cutter buffer cycle stock = spare cutter buffer daily usage × spare cutter buffer lead time
Required spare cutter buffer inventory = cycle stock + spare cutter buffer safety stock

Inputs explained

Spare cutter buffer on hand:
Cutter consumption per day:
Cutter replenishment lead time:

How to use the result

Use it to set cutter reorder points and to reassess stock when ground conditions change consumption on a live drive.
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.

Current U.S. benchmarks

Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you size a spare cutter buffer for a TBM? Divide cutters on hand by daily consumption to get days of supply, then check it against replenishment lead time. Here 1,200 cutters at roughly the modeled usage give about 12.83 protected days of supply.
What is a good days-of-supply for TBM cutters? Enough to comfortably exceed your replenishment lead time with margin for a wear spike. In this example the protected days of supply is 12.83 days against an unprotected figure of 14.12 days — the difference is the cushion the buffer provides beyond raw consumption.
Why does cutter consumption vary so much? Cutter life depends on ground abrasivity, face pressure, boulders, and rpm. Hard, abrasive rock or a mixed face can multiply wear rates several times over the design assumption, which is exactly why a steady-average buffer needs headroom.
What happens if I run out of spare cutters? You either stop the machine and wait for a shipment — burning ring-build and standby cost — or launch an unplanned intervention to swap tools, both of which cost far more than carrying a larger buffer. That asymmetry is why cutter stockouts are treated as a serious schedule risk.
Cycle stock vs safety stock for cutters — what's the difference? Cycle stock is the routine quantity you expect to consume over a replenishment cycle. Safety stock is the extra held specifically to absorb wear spikes and lead-time slips. Both feed the total buffer, but only safety stock protects you when the ground turns nasty.

Last reviewed 2026-05-12.