Tunnel Boring & Heavy Civil Equipment worked example

Cutterhead Fabrication Cost at 61% first-pass weld yield: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop first-pass weld yield to 61%, then walk the calculation through step by step. Estimates the shop cost to fabricate a TBM cutterhead from disc-cutter housing count, per-pocket build rate, weld yield, and one-time hub tooling.

The inputs for this scenario

  • Welded cutter housings in the build: 48 housings (held at the documented default)
  • Fabrication cost per welded housing: 3,200 $ / housing (held at the documented default)
  • First-pass weld yield: 61 % (the input this scenario stresses; the baseline uses 85)
  • Hub and bearing-plate machining setup: 95,000 $ (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Total = housings x fabrication rate x (first-pass yield รท 100) + hub setup.
  • Total cutterhead fabrication cost works out to 188,696 $ at these inputs, and this is the headline figure for the scenario.
  • Cutterhead fabrication cost per unit works out to 3,931 $ / piece at these inputs.
  • Variable cutterhead fabrication cost works out to 93,696 $ at these inputs.
  • Fixed cutterhead fabrication cost adder works out to 95,000 $ at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where first-pass weld yield sits at 85% and the headline result is 225,560 $, this scenario comes in 16.34% below the baseline at 188,696 $.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to first-pass weld yield, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It models yield-adjusted fabrication and fixed hub setup, but not weld repair labor, NDT cost, or the fit-up and assembly of the completed cutterhead.

Results at a glance

  • Total cutterhead fabrication cost: 188,696 $ (headline result)
  • Cutterhead fabrication cost per unit: 3,931 $ / piece
  • Variable cutterhead fabrication cost: 93,696 $
  • Fixed cutterhead fabrication cost adder: 95,000 $

Run it with your numbers

  • To rerun this with your own numbers, open the live Cutterhead Fabrication Cost calculator, set first-pass weld yield to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.