This work presents an experimental investigation of the effect of different factors including normal load, workpiece surface roughness, and fixture roughness, on the coefficient of friction along the workpiece/fixture contact for machining processes. A full factorial design of experiment was used. Randomization, blocking, and averaging schemes were utilized to reduce the experimental error and variability. The data was statistically analyzed and explanations for the observed trends were given. This investigation is part of an ongoing research project to develop an integrated modular dynamic model of the milling process including the effect of fixture dynamic.