Tunnel boring is only partly about boring the tunnel itself, bracing the tunnel and removing the spoils probably take as much time as boring the tunnel itself.
It’s a complex process with work crews, management layers, multiple subcontractors, multiple stakeholders, etc. Replacing the tool on a CNC mill with a tungsten carbide tool takes what, a few minutes? Assuming you already have the tool.
It’s also insanely easy to verify a tungsten carbide CNC tool is 10x faster at cutting metal than high speed steel vs. testing ‘This tunnel boring machine will be 10x faster.’
It’s a complex process with work crews, management layers, multiple subcontractors, multiple stakeholders, etc. Replacing the tool on a CNC mill with a tungsten carbide tool takes what, a few minutes? Assuming you already have the tool.
It’s also insanely easy to verify a tungsten carbide CNC tool is 10x faster at cutting metal than high speed steel vs. testing ‘This tunnel boring machine will be 10x faster.’
One takes minutes, the other takes years.