INTRODUCTION A cam/follower system will fail to perform its intended function adequately if the surfaces of the cam and/or the follower are worn excessively. This type of service failure can often be avoided if the system is designed such that an adequate lubricant film is present in the contact region throughout the life of the system. Therefore the prediction of the thickness of such a lubricant film under a variety of operating conditions is a vital step in the systematic design of a cam mechanism (see Reference 29). This Data Item presents a procedure for calculating values of lubricant film thickness in the contact region between a disc cam and its follower (either rolling or sliding contact). To determine film thickness it is necessary to find the radius of curvature of the cam profile@ the lubricant entrainment velocity and the contact force at the interface between the cam and the follower for a series of angular positions of the cam. This analysis is time consuming and is best carried out using the FORTRAN computer program (ESDUpac A9408) supplied with this Data Item. The program determines values of minimum film thickness at intervals of one degree of cam rotation (assuming constant angular velocity of the cam) and finds the smallest value of film thickness during the cycle. The program can be used to determine suitable values of rate and preload for a return spring designed to ensure that the cam and follower remain in contact. Alternatively@ if a spring of known rate and preload is specified the program checks that contact is maintained. A check to ensure that profile undercutting (see Reference 24) does not occur is also included. The calculation method presented in this Data Item is based on the theory of elastohydrodynamic lubrication (see Reference 33) in which changes in the viscosity of the lubricant and elastic deformation of the components in contact are significant. The ESDU Tribology Sub-series contains procedures for calculating film thicknesses in lubricated Hertzian contacts and these are given in Data Item 85027 (2D-line contacts) and Data Item 89045 (3D-point contacts)@ respectively. Computer programs (ESDUpacs A9137 and A9138) that implement these procedures are also available (see References 22 and 23). The algorithm used to calculate film thickness in the program (ESDUpac A9408) supplied with the current Data Item is exactly the same as that used for the line contact part of ESDUpac A9138 (for the reasons discussed in Appendix A).