One key component in panelboard production is the fiber refiner which grinds cellulose woodchips into slender fibers. Current fiber refiners are rotating machines where the grinding takes place between a stator and a rotor. The rotor can be supported by preloaded spherical roller thrust bearings (SRTB) which for simplicity are often modeled as springs with radial stiffness. However, a more detailed analysis of these bearings shows that other stiffness components are also present. Thus, the aim of this paper is to show how dynamic properties change as such stiffness components are introduced.The SRTB stiffness matrix is derived from a simplified finite element model. This derived stiffness matrix is then used in another rotordynamic model. Campbell diagrams show that these additional stiffness components influence the eigenfrequencies in such a way that they should be considered when analyzing fiber refiners.