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One of the references in the article mentions using better alloys ("modified tool steel") and 20" discs produces better results and lower overall costs due to t

by Hilift 2y ago

One of the references in the article mentions using better alloys ("modified tool steel") and 20" discs produces better results and lower overall costs due to time between disc replacement. This could be A8 "chipper knife" steel. https://www.robbinstbm.com/wp-content/uploads/2017/07/Smading_20InchCutters_RETC2017.pdf https://www.robbinstbm.com/wp-content/uploads/2017/07/Smadin... https://www.litechtools.com/products/tbm-disc-cutter/ https://www.litechtools.com/products/tbm-disc-cutter/

timschmidt 2y ago
Makes sense. I was thinking more about the face of the machine itself being larger, likely the size of the tunnel, and would contain many such 20" discs. In other words, given that the material removal rate of each disc is likely fairly similar from machine to machine, the machine with more of them removes more material at once.
- freeopinion 2y ago
  It seems self-evident that all additional material removed has 0 additional value. In fact it has negative value because it increases the requirements for any support or finish materials. So energizing and consuming 7/4 more discs is just pure waste. It also adds disposal costs. The most obvious argument I can think of to support this approach is if the excess material could be sold at a profit. But that seems dubious.
  - timschmidt 2y ago
    > So energizing and consuming 7/4 more discs is just pure waste. That is and assumption and not self evident. There are lots of reasons one might want to use many cutters. It is a common practice in wood and metal machining, for instance[1]. Having additional cutting surfaces reduces the rate of wear, provides redundancy in case of chipping, increases the mean time between required services, allows cutters to run cooler, reduces chatter, improves surface finish, and a host of other reasons. Seems like you could research it. 1: https://www.advancedmachinery.co.uk/content/product/8500_0_z.jpg https://www.advancedmachinery.co.uk/content/product/8500_0_z...
  - LargoLasskhyfv 2y ago
    You seem to have focused your 'tunnel vision' on the costs of boring that thing alone. Sort of CAPEX, so to speak. But what about less OPEX later, because of more flexibility, less maintenance burden, when other demands arise or conditions change? If the tunnel is wide enough, two tracks can be built side by side, and another level of two tracks on top of it. That makes room for a total of four (potential) tracks, with the possibility to switch between them not only horizontally, but also vertically via ramps (inside that tunnel profile). It also enables single platform stations for one track on one or two of the two possible levels in such a tunnel. Without any further 'big digs', or blocking the line altogether.
freeopinion 2y ago
The larger TBM would require ~7/4 more discs. So you might go a longer time between disc changes, but each disc change requires 7/4 more effort and material. Any hypothetical savings in spin-up and spin-down would be offset. If the balance came out to some advantage, it would not be due to a larger diameter of the TBM. It would just indicate that you should consider retrofitting the smaller diameter TBM with thicker discs.

by Hilift 2y ago

timschmidt 2y ago

Makes sense. I was thinking more about the face of the machine itself being larger, likely the size of the tunnel, and would contain many such 20" discs. In other words, given that the material removal rate of each disc is likely fairly similar from machine to machine, the machine with more of them removes more material at once.

freeopinion 2y ago
It seems self-evident that all additional material removed has 0 additional value. In fact it has negative value because it increases the requirements for any support or finish materials. So energizing and consuming 7/4 more discs is just pure waste. It also adds disposal costs. The most obvious argument I can think of to support this approach is if the excess material could be sold at a profit. But that seems dubious.
- timschmidt 2y ago
  > So energizing and consuming 7/4 more discs is just pure waste. That is and assumption and not self evident. There are lots of reasons one might want to use many cutters. It is a common practice in wood and metal machining, for instance[1]. Having additional cutting surfaces reduces the rate of wear, provides redundancy in case of chipping, increases the mean time between required services, allows cutters to run cooler, reduces chatter, improves surface finish, and a host of other reasons. Seems like you could research it. 1: https://www.advancedmachinery.co.uk/content/product/8500_0_z.jpg https://www.advancedmachinery.co.uk/content/product/8500_0_z...
- LargoLasskhyfv 2y ago
  You seem to have focused your 'tunnel vision' on the costs of boring that thing alone. Sort of CAPEX, so to speak. But what about less OPEX later, because of more flexibility, less maintenance burden, when other demands arise or conditions change? If the tunnel is wide enough, two tracks can be built side by side, and another level of two tracks on top of it. That makes room for a total of four (potential) tracks, with the possibility to switch between them not only horizontally, but also vertically via ramps (inside that tunnel profile). It also enables single platform stations for one track on one or two of the two possible levels in such a tunnel. Without any further 'big digs', or blocking the line altogether.

freeopinion 2y ago

The larger TBM would require ~7/4 more discs. So you might go a longer time between disc changes, but each disc change requires 7/4 more effort and material. Any hypothetical savings in spin-up and spin-down would be offset. If the balance came out to some advantage, it would not be due to a larger diameter of the TBM. It would just indicate that you should consider retrofitting the smaller diameter TBM with thicker discs.