309 Figure 1 – Cutting mechanics of point attack tool cutting system (Dey 2018) In general, it is found that the rake angle, wedge angle and clearance angle has important role in rock cutting. Rake angle is more or less kept between 20 to 25 degree. Wedge angle and clearance angle values are fixed depending on the strength and formation of the rock medium (Dey and Ghose, 2009). However, a cutting system can be selected considering – (i) rockmass properties, (ii) final product characteristics and (iii) application type (Dey, 1999). Therefore, any design consideration must possess two basic elements – the machine and the rockmass (Dey and Ghose, 2008). Rockmass is naturally formed and cannot be imitated, but a machine can be designed to suit the requirement (Eskikaya and Tuncdemir, 2007). “The understanding of the cutter-rock interaction is termed as “Cuttability” and “Cuttability” can be defined as the easiness to cut for a particular cutter-rock interaction” (Dey and Ghose, 2011). Thus, “Cuttability” of is influenced by (i) rock/rock mass parameters, (ii) machine parameters and (iii) the type of application, as given in Table 1. Table 1 – Parameters influencing cuttability (Dey and Ghosh, 2010) Geo-technical properties Machine properties Type of Application density, brittleness, unconfined compressive strength, point load index, Young’s modulus, specific fracture energy, toughness index, tensile strength, sonic velocity, abrasivity volumetric joint count, stickiness of material Cutting tool configuration - rake angle, attack angle, clearance angle and tip angle, pick lacing, type of pick number of picks, tip material, machine weight, engine power, nature of coolant for tips Direction of cutting, length, height and width of operating area, operator skill, specific requirements dry/wet, fragmentation desired and output A number of rockmass classification approach to define cuttabaility of different excavation systems are available. Some of the notable cuttability indices are - Discontinue Strength Classification (Franklin et al., 1971). This was followed by Excavation Index (Kirsten, 1982), Geological Factors Rating Scale (Minty and Kearns, 1983), Engineering
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