## 4 Results  
The specific cutting energy can be expressed by Equation (1), and the specific drilling energy by Equation (2):  
\[SE_{\mathrm{C}}=\frac{E_{\mathrm{Cav}}}{V_{\mathrm{C}}} \tag{1}\]  
\[SE_{D}=\frac{E_{\mathrm{Dav}}}{V_{D}} \tag{2}\]  
where \(SE_{\mathrm{C}}\) is the specific cutting energy (J/m\({}^{3}\)); \(SE_{D}\) is the specific drilling energy (J/m\({}^{3}\)); \(E_{\mathrm{Cav}}\) is the average energy expended on rock cutting (J); \(V_{\mathrm{Cav}}\) is the volume of rock fragments formed by cutting (m\({}^{3}\)); and \(V_{D}\) is the volume of rock fragments formed by drilling (m\({}^{3}\)). Calculation of Specific Cutting Energy and Specific Drilling Energy from Results of Laboratory Measurements  
The cutting element of the device for linear rock cutting moves horizontally in relation to the surface of the rock sample. Therefore, the horizontal component of the cutting force performs mechanical work along the distance made, which is equal to the average length of the sample. The formation of rock fragments is of a discontinuous nature [34], which can be seen in the variation of the horizontal cutting force in time (Figure 3). In the figure, the green line represents the beginning of cutting, and the red line represents the end of cutting. Figure 3: Diagram of the dependence of the horizontal component of the cutting force of one cutting element on time. The average horizontal component of the cutting force of one cutting element is calculated according to the equation:  
\[F_{\text{cav}}=\frac{\sum_{i=1}^{N}F_{\text{c}i}}{N} \tag{3}\]  
where \(F_{\text{cav}}\) is the average horizontal component of the cutting force of one cutting element (N); \(F_{\text{c}i}\) is the horizontal component of the cutting force of one cutting element and \(N\) number of samples. Since one cutting element was used to cut the rock samples in the laboratory tests, the average energy used on rock cutting is equal to the average energy used on cutting the rock of one cutting element. The expression for calculating the average energy used on cutting rocks of one cutting element is:  
\[E_{\text{Cav}}=E_{\text{cav}}=F_{\text{cav}}\cdot L_{\text{cav}} \tag{4}\]  
where \(E_{\text{cav}}\) is the average energy used on rock cutting of one cutting element (J); \(L_{\text{cav}}\) is the average cut length (m). The volume of rock fragments formed by cutting one cut is calculated using the equation:  
\[V_{\text{C}}=\frac{m_{c}}{\rho}=\frac{\frac{m_{c1}-m_{c2}}{n_{\text{c}}}}{ \frac{m_{\text{d}}}{\text{V}_{\text{ns}}}}=\frac{V_{\text{rs}}\cdot(m_{\text{ c1}}-m_{c2})}{m_{\text{dr}}\cdot n_{\text{c}}} \tag{5}\]  
where \(m_{\text{c}}\) is the mass of rock fragments of one cut (kg); \(\rho\) is the bulk density (kg/m\({}^{3}\)); \(m_{\text{c1}}\) is the sample mass before cutting (kg); \(m_{\text{c2}}\) is the sample mass after cutting (kg); \(n_{\text{c}}\) is the number of cuts; \(m_{\text{dr}}\) is the dry mass of the sample (kg); and \(V_{\text{rs}}\) is the volume of the rock sample (m\({}^{3}\)). The movement of the cutting element of the drill bit, i.e., the diamond grain is a complex movement consisting of vertical movement and rotation around the vertical axis, so the total mechanical work is equal to the sum of mechanical works created by the vertical component of drilling force upon vertical movement of the drilling bit and the horizontal component of drilling force by a circular arc (Equation (6)). The diamond grain rotates at some distance from the axis of rotation and forms the arm of the force to the horizontal component of the drilling force, whereby a torque (torsion) is created:  
\[E_{\text{Dav}}=E_{\text{DNav}}+E_{\text{DBrav}} \tag{6}\]  
where \(E_{\text{DNav}}\) is the average energy used on rock drilling generated by the action of the vertical component of the drilling force (J); \(E_{\text{DBrav}}\) is the average energy used on rock drilling generated by the action of torque (J).