The ranking of the Pareto solutions for CF/PEKK and CF/epoxy can be found in Fig. . The most satisfactory solutions (Rank1) are summarized in Table .Two composites showed the same optimal spindle speed (5308 rpm), but the optimal feed rate (Ff = 0.144 mm/rev) of CF/PEKK is 152.6% higher than that of CF/epoxy. The different optimal drilling parameters obtained for the two composites can be attributed to the disparate drilling performance as a result of their distinctly different mechnical and thermal properties. CF/PEKK delamination damage is highly sensitive to temperature (especially when approaching/exceeding Tg). This can soften the composite plies and deteroriate their resistance against bending-induced interlaminar fracture . Therefore, low feed rate that leads to severe heat accomulation should be avoided for CF/PEKK, as indicated in Fig. . For CF/epoxy on the other hand, its delamination damage is more sensitive to high thrust force as a result of its low Mode-I interlaminar fracture toughness , but less susceptible to high temperature as shown in Fig. . As such, high feed rate should be avoid for CF/epoxy in order to minimize severe delamination damage. Under the optimized drilling conditions, although CF/PEKK generates 134% higher thrust force than CF/epoxy, it can still achieve satisfactory hole quality with acceptable delamination damage (Fda < 1.4) and 13.5% lower maximum hole wall temperature. Most importantly, CF/PEKK shows more superior machinability as compared to CF/epoxy, with 152.6 % higher MRR.