Add to ORKGIn this paper, we aim for an improved understanding of the causes for torsional vibrations in rotary drilling systems that are used for the exploration of oil and gas. For this purpose, an experimental drill-string set-up is considered. In that system, torsional vibrations with and without stick-slip are observed in steady-state. In order to obtain a pre-dictive model, a discontinuous static friction model is used. The parameters of the suggested model are estimated and the steady-state behaviour of the drill-string system is anal-ysed both numerically and experimentally. A comparison of numerical and experimental bifurcation diagrams indi-cates the predictive quality of the model. Moreover, spe-cic friction model characteristics can be lin...