Comparative tests of rock drill bits for piston machines

"The object of this thesis is to find out the relative cutting qualities of different kinds of rock drill bits. The bits tested were: the regular cross bit, the Z bit of the Southeast Missouri type and the bull bit of the Joplin type. All these bits were made on a No. 5 Leyner sharpener and were tempered as nearly alike as possible. All conditions were kept as nearly uniform as possible during the various tests; air pressure, length of stroke, size of bit, etc., the only variables entering being the difference in bits and personal equation of operators"--Introduction, page 1.