Conventional fluted twist drills have the problem of excessive wear at the diametrical corners formed between the land clearance surface or margins on the flutes and the drill point cutting edges. Once wear begins at these corners it propagates rapidly and results in a drill that is rendered unusuable. Furthermore, conventional fluted twist drills produce the cutting action only at the drill point cutting edges and at the chisel edge. It is known that conventional twist drills are end-cutting tools in which the flutes are employed for the admission of cutting fluid and coolant and for the ejection of the chips. Normally, conventional twist drills divide into heavy duty and high helix or fast spiral drills. Heavy duty drills have great strength in the web and possess great rigidity which is suitable for severe drilling conditions in tough alloy steel, steel forgings and hard cast ferrous materials. The high-helix drills have a higher helix angle and are intended for deep holes where clearing chips from the hole is important.
Heat is the primary cause of drill failure. The major place for heat to be generated is at the intersection of the cutting edges and the margins. When a drill gets hot it softens the material and a plating action occurs between the material being drilled and the drill. As the plating progresses, friction increases since the margins have the highest peripheral speed and absorb heat rapidly. Heat introduces the further problem of thermal expansion of the drill diameter across the margins. Drilling a material like titanium results in the drill expanding faster than titanium which causes high side forces at the margins, and galling or plating occurs rapidly. If the drill has a heavy or thick core, chip clearance is restricted and the result is additional heat generation, higher torque and early drill failure. A drill sharpened off-center can encounter some or all of the problems noted above. After heat starts to rise in the drill point, a chain reaction occurs through expansion, increased friction, cutting edge softening, and plating, and each reaction fortifies the others.