Experiment methods and materials. Thin sections under cross-polarized light of the rock materials used in this work, i.e., Rorschach sandstone (a) and Grimsel granite (b). The experiment testing concept and the parameters measured to investigate rock–bit interaction are shown in c. During the experiments, the tool scratches the rock surface along a prescribed scratch distance (c.1), flattening the tool tip (c.2), which is optically imaged and investigated after the test. The tool penetration (c.3) and cutting forces (c.4) are monitored during the experiment. After the test, knowledge of wear flat and tool penetration enables determining the tool’s contact surface (c.5). During the test, the total, vertical tool displacement is monitored (d) and afterwards processed, together with the wear flat at the tool tip to assess the actual penetration of the tool. During the test, the cutting forces exerted on the tool are measured as well (e). d, e The total displacement and cutting force signals obtained during several tests (thin lines), while the moving-averaged signal (thick line) is shown for comparison for the untreated sandstone material, together with the \(\pm 10\%\) interval.