on the drill bit cones can become such that the tungsten carbide is prematurely chipped or broken to an extent which will markedly reduce the life of the cutting structure to an undesirable level and drastically increase the cost per foot of hole drilled true rolling action while well known in the drill bit industry as a means for the cutting element on the cone member to impart 34 pure compression 34 loading on bottom in actuality is generaly not 34 pure 34 true rolling but is instead a compromise by the bit designer to satisy geometric desirabilities such as providing the largest cone diameters and bearings possible in a given hole size these geometric parameters can be and usually are accomplished by using intermesh of cone rows and accepting an amount of non true rolling more or less depending upon the designers 39 judgement of the drilling condition expected in the bits illustrated in fig4 7 34 pure 34 true rolling cone elements are shown upon which the tips or ends of the insert cutting elements are placed excepting only the gage row and one nose row on each cone so that essentially the entire cutting structure is in a true rolling mode and all carbide inserts are rolling on bottom point a shown in fig4 generates a locus of travel as shown in fig5 and thus exerts a force on the formation which is purely compressive in nature the compressive unit loading force is known by those familiar with the requirements for drilling in very hard friable formations as the principal mode for applying energy to effect the destroying of the formaton to be cut it follows that the present design which limits its action on bottom to compressive loading alone is thus superior to.