A new type of carbide-tipped twist drill has been successfully developed in order to drill steel workpieces at considerably higher feed speed than that of the conventional HSS twist drills. Design principle, cutting mechanism and capability of this new carbide drill are discussed with reference to a conventional HSS drill. The new carbide drill is characterized by special shapes of the cutting edge, the chip pocket and the flute. It has been ascertained experimentally that the special edge shape makes the tool free from edge chipping which occurs otherwise in steel cutting. Also the chip pocket and the flute design guarantee both periodic fracture and smooth transport of the chip along the flute. Drilling forces for the carbide drill have been experimentally known to be greater than that of conventional HSS twist drills. The carbide drill gives fairly closer hole accuracy than the HSS drill.
