Abstract: A pressure compensating lubrication system for sealed bearing earth boring bits having a lubricant reservoir fitted with a piston. A spring member is disposed between one end of the reservoir and the piston. The spring member applies pressure through the piston to the lubricant in the reservoir and bearing and absorbs pressure fluctuations in the lubricant generated while drilling.

Abstract: An earth boring drill bit has hard metal inserts in its cutter shells that are spaced to eliminate rows. Each insert has a surrounding boundary zone with inner and outer loops corresponding to the minimum and maximum desired distances between centerlines of inserts, respectively. Each insert has at least one insert located randomly in its boundary zone. In selecting the locations, a first insert is arbitrarily located. The location of a second insert is randomly selected within the boundary zone of the first insert. The location of a third insert is randomly located within the boundary zone of the second insert, so long as it does not come any closer to the first insert than the minimum desired distance between inserts. Each succeeding insert is chosen in this manner.