The response surfaces of Tmax of CF/PEKK vs. CF/epoxy are depicted in Fig. (b). For both composites, the maximum hole wall temperature showed a significant decline with feed rate, as high feed rate can reduce the tool-workpiece engagement time and eliminate the heat accumulation effect. It is notable that the Tmax of CF/PEKK has exceeded/approached its glass transition temperature (Tg = 160 ℃) at low feed rate, however the CF/epoxy Tmax has never exceeded its Tg (130 ℃). For both composites, the Tmax firstly increased and then decreased with spindle speed. The initial increasing trend can be attributed to the enhanced tribological interaction at high relative speed between the tool and the workpiece , which accelerated the frictional heat generation. As the spindle speed further increased, the tool-workpiece contact time was significantly shortened, hence reducing the heat accumulation effect. In comparison with CF/epoxy, the Tmax of CF/PEKK is up to ~100 ℃ higher. The drilling induced CF/epoxy chips are mostly in powdery form according to previous studies by Ge et al. and Xu et al. . Due to thermoset epoxy's better thermal stability, the softening of CFRP under machining induced high temperature is rather limited. The fine chips are relatively stiff and can be evacuated efficiently, resulting in minimum chip/tool bit interaction. In contrast, CF/PEKK is highly thermosensitive. The severe softening of the material leads to adhesion of continuous ductile CF/PEKK chip onto the cutting tool.