rotary earth boring bits according to the present invention and method of assembly thereof allow development of a rotary earth boring bit construction of low cost nature and having exceptionally good wear life . the drill construction promotes the use of optimum bearing materials for rotary support of the cutters of the drill thereby promoting exceptionally good service life . additionally , the bearing of each cutter assembly may be lubricated so as to further enhance the service life of the drill . assembly may be accomplished at low cost by taking advantage of dimensional changes of the parts responsive to heating or cooling . the drill cutter may be heated to increase the dimension of the bearing cavity formed therein while the bearing and its support spindle may be cooled to reduce the external dimension of the bearing . following assembly of the bearing and spindle to the cutter a tight retention fit will develop between the bearing and cutter as these parts approach normal temperature . to further insure retention of the cutter in assembly with the bearing , a retainer element may be located during assembly within registering retainer grooves formed in the cutter and bearing .