Automating the excavation function of an excavator is a complex control problem, because of the nature of the interaction between the cutting tool and the medium and the many parameters that are involved in the process. A fundamental question that is not yet resolved is the choice of parameters to be used in a feedback loop for the control of the process, and the control algorithm. Based on a previous proposition for the control algorithm to be used for this purpose, knowledge about the forces involved may be used for adjusting the motion of the bucket. In this paper, some results of experimental measurements of the excavation forces are presented. These forces cannot be measured directly on the bucket, but the kinematic and dynamic relations can serve for this purpose. The paper talks about the development of these relations, and then the results are presented and discussed.