The effect of guide ways friction on axis dynamics has been evaluated computing, on the FEM model without position control (i.e. the axis is free to move), the dynamic compliance at the work piece with varying values of viscous damping at carriages (i.e. without static friction). As discussed for cases (A) and (B) in chapter 4.1, increasing C moves mode (A) to a higher frequency and mode (B) to a lower frequency. Another typical case is (C): some vibration modes aren’t influenced at all by guide ways damping because their shape doesn’t involve a significant displacement at the guide way. It can be noticed that different modes ask for different optimal damping values: it is therefore necessary to choose the best tradeoff, taking into account how each mode influences machine performance.