The surface area of the head of a tunnel boring machine is usually flat. A cone-shaped head would increase the surface area. The question is if it could speed up the boring process.

I know that with current machines the boring process is also limited by other factors. But that is not part of the question.

  • $\begingroup$ The forward force which pushes the drill bit into rocks would be concentrated however that is not the case for flat surface cutter, and how do you smooth the the tunnel walls after boring ? you need again a flat smoother. That's what i suggest not necessarily the real reason behind the design. $\endgroup$ – Sam Farjamirad Oct 14 '18 at 9:16
  • $\begingroup$ Surface area doesn't matter directly, since what you're after is parameters like total cut depth per rotation -- not to mention the waste removal capabilities. $\endgroup$ – Carl Witthoft Oct 15 '18 at 18:48

Because with a flat head the waste material can be (relatively easily) collected and removed from the cutting face.

With a cone-shaped bit that removal is not so easily accomplished.

Cone-shaped bits tend to be used to push or compress the material out of the way, which is fine for "softer" materials ...

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    $\begingroup$ another aspect of flat plate boring heads is that the cutting tools can be replaced from the non-cutting side. That would be nearly impossible with a cone head (from France). $\endgroup$ – fred_dot_u Oct 14 '18 at 11:07
  • $\begingroup$ @fred_dot_u along that line of thinking, imagine if big Bertha in seattle was a cone shaped drill.... $\endgroup$ – Aethenosity Oct 15 '18 at 19:23

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