One of the problems in machining of composites is related with the fibers as reinforcement, due to their abrasiveness, causing fast tool wear and deterioration of machined surface. Among all the damages that can occur in the drilling of a composite plate, delamination is the most serious, as it can cause loss of mechanical strength of laminate plates. The main mechanism responsible for delamination is the axial thrust force exerted by the stationary center of the drill – chisel-edge – whose action is more similar to an extrusion that to a drilling. It can be shown that 40% to 50% of the thrust force is because of the chisel edge. Therefore, in this paper a new set of hollow drill bits is introduced and tested on the composite materials with different properties and drilled hole quality mainly, surface roughness, roundness, hole oversize and delamination investigated. With these hollow drill bits we were able to achieve lower thrust forces. Also drill bit geometry changed to be optimized for the best hole quality.

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