Abstract This paper presents the results of a study investigating cutting response of a single worn PDC cutter with special attention on the friction on its wear flat which is badly understood in litterature. So, consider a cutter with horizontal wear flat fixed on a rotating bit with vertical axis. In order to identify frictional forces acting on the wear flat, experiments are conducted on a single worn cutter with a constant applied vertical force on a rotative sample. They show a relationship between imposed vertical load on the cutter and penetration angle α, which is related to the helicoidal movement of the tool. In the same way, the mechanical model is a flat rigid punch sliding parallely to a horizontal surface with the inclination α. The numerical finite element model uses a steady algorithm which allows, in a reference moving with the cutter, to treat the stationary problem on a fixed geometry. The previous relationship was confirmed and it was found too that the frictional mechanism is related to a deformation of elastoplastic type, so, dilatancy and contractancy are discussed using alternative elastoplastic models.