The response surfaces of thrust force for the two composites are shown in Fig. . It is clear that for both composites, the thrust force shows significant increase with feed rate and decreases slightly with spindle speed, see Fig. ). This shows good consistence with the findings reported in drilling of CF/PEEK and CF/epoxy . The drastic increase of thrust force with feed rate can be explained by the considerably increased thickness of material being removed and the slight declining of thrust force with spindle speed can be as a result of the thermal softening of matrix under high temperature induced by the enhanced tribological interaction .