Fig. 3

Tool penetration and wear flat in sandstone. Tool penetration during testing of Rorschach sandstone is shown, with the scattered data and the left y-axis for untreated (violet squares) and after treatment (green circles). The symbol sizes represent the wear flattening of the cutting tool (see legend in the figure). The bi-linear regressions of the tool penetration values along the scratch distance are shown as dashed black lines. As a bar plot, we also include the wear flat increase per unit of scratch distance, here called wear slope, where the values are provided by the right y-axis. The bars indicate the wear slope for untreated (violet) and after-treatment (green) conditions, shown as contiguous columns for the scratch distance ranges 0–4 mm, 4–8 mm, 8–15 mm and 15–90 mm