## 2 Materials and Methods  
The entire production process included a large number of variables that could affect the final product. In this study, attention was paid to the selected parameters, such as cutting tool geometry, cutting speed \(v_{c}\), feed, and cutting depth \(a_{p}\), which have a great influence on the evaluation of thin-walled bearing rings. The experiments covered three groups of samples machined with respective cutting tools of different geometry denoted WIPEP, STANDARD, and XCEL. The cutting tool cubic boron nitride (CBN) inserts produced by Sandvik (Stockholm, Sweden) were used as follows:  
* WIPER: insert CNGA120408T01030 AWH class 7015 with WIPER geometry;
* STANDARD: insert CNGA120408S01030A with corner radius 0.8 mm;
* XCEL: insert CNGX1204L025-18 XA class 7015 with XCEL geometry. The XCEL geometry has a straight edge with a small cutting-edge angle. This geometry helps to form thin chips, and the temperature at the cut point is reduced, slowing down of the development of wear in the form of a groove. Figures 1 and 2 present the inserts WIPER and XCEL, as well as the holder used in the experiments. It is clearly seen why no radius is given for the XCEL geometry. Figure 2b explains the geometrical difference between STANDARD and WIPER. The latter has multi-radii tool nose shaping designed for finish machining, where an additional flat section gives a smoother surface to the machined surface at a feed rate that is higher than usual [26]. The samples of bearing rings were made out of steel 100 Cr6 (14 109.4) after thermal treatment as follows: normalizing annealing at 860 \({}^{\circ}\)C; soft annealing at 70 \({}^{\circ}\)C; cementation at 840 to 870 \({}^{\circ}\)C; quenching at 780 to 880 \({}^{\circ}\)C (oil to water); and tempering at 160 \({}^{\circ}\)C for 1 h. The declared properties were: strength \(R_{m}\) min. 785 MPa, \(R_{e}\) min. 590 MPa, and hardness min. 239 HB. The cutting operation was performed with a 3-axes machine tool Famar SUB160 (Famar, Avigliana, Italy). Since the producers recommended different machining parameters for each type of the cutting edge, it was decided to not repeat experiments in the same conditions for all tools, but to choose the most suitable settings for the respective geometries. Table 1 shows the experimental cutting parameters classified according to the group of samples. Figure 1: Experimental setup: (**a**) the holder with cutting insert; (**b**) insert CNGX1204L025-18 XA class 7015 with XCEL geometry. The surface integrity of the machined bearings was assessed through the measurement of 2D roughness, 3D topography, and residual stresses of the outer layer. A large variety of surface measuring devices are available, from mechanical stylus profilometers and non-contact optical ones, to the scanning probe microscopes to be selected from in order to acquire either a cross-sectional profile or the areal topography information of the examined surfaces [27]. Some of the most recent reports cover investigations on optical measurement [28], especially diffractive relief structures [29] and interference microscopy [30] with confocal and spiral scanning [31], including comparative studies of different techniques [32]. Some researchers also discuss the comparability of different surface parameters obtained from profile and areal measurements [33; 34]. In the present study, profile and topography parameters were measured using a 3D optical microscope Alicona Infinite-Focus G5 (Alicona, Graz, Austria). Its maximal measured area was 40,000 mm\({}^{2}\) at 2.5\(\times\) zoom and 990 mm\({}^{2}\) at 100\(\times\) zoom. For profile parameters, minimal mean arithmetic deviation of the profile at maximal zoom can be measured \(Ra=0.03\) um, while for the topography measurement, the respective minimal measured value mean arithmetic height of the limited scale of the surface was \(Sa=0.015\) um. All profile parameters were measured under the conditions specified in ISO standards.