Rock cutting mechanisms were used for the prediction of the cutting performance of mechanical excavators in the mid of 1900s. However, rock cutting tests performed in the laboratory both in small and full scales have been successfully applied for the same purpose as a more realistic method for the last few decades. Daily advance rate, the specificenergy, and the performance of the excavation machine can accurately be predicted by means of those tests. In accordance with the advanced technology, the cutting tests can also be modeled by utilizing the discrete element method as in Particle Flow Code in 3D (PFC3D) and hence the performance of a machine can be assessed from this code as well. This paper initially summarizes the methods which have been applied to predict the forces. Then, rock cutting simulations by using a conical bit in PFC3D are discussed and the pick forces recorded in the course of modeling are given. The results are compared with the ones obtained from rock cutting mechanisms. In addition, an understanding of how discrete assemblies are failed during cutting and how the tool forces on the bit are influenced by the failure type are examined.