TOOL STEEL EOR THE UNITED STATES NAVY. 349 



tools. Electrical observations were made of the input to the motor which 

 drove the test lathe. They showed, as on the previous test, that the work 

 done by the tools varied. It was therefore decided to compute the "work 

 value" or watt-minutes of work done by each tool first, and then adjust the 

 "work values" by the principles of least squares instead of elapsed time of 

 runs, as was done in the previous test. By the previous method an observa- 

 tion of the elapsed time of run of a tool might vary so greatly from the mean 

 that it would be rejected, although the watt-minutes of work done by a tool 

 might not vary sufficiently from the mean work value to necessitate rejection. 

 The work done by a tool, which is indicated by the elapsed time of run and 

 the watts consumed, is an important factor in determining selection, and it 

 was therefore decided that the "work value" of each tool was a fairer value 

 to adjust by the principles of least squares than the elapsed time of runs. 

 The relative values of the tool steels were computed as previously explained, 

 and the data of this test, together with the chemical analyses of the tool 

 steels, are given on sheet No. 1520, Plate 144. 



A test was made of the tools which obtained the highest selective factor 

 under Schedule 3893 under the same conditions as the above selective test, 

 and the data are recorded under the heading "4 Schedule 3893" on sheet 

 No. 1520, Plate 143. 



CARBON TOOL STEELS. 



Schedule 38 qj. — The information obtained from the selective test con- 

 ducted under Schedule 3244 indicated that it was advisable to revise the 

 specifications for carbon tool steels given in Appendix A, and a selective test 

 similar in character and purpose to that previously described was introduced. 

 Four classes of carbon tool steel were selected which varied principally in 

 their carbon content. The specifications finally prepared are given in 

 Appendix C. The conditions throughout the selective test were maintained 

 as nearly constant for each class of tool steel as facilities would permit, 

 and the elapsed time of run, or operating life of the tools, was the principal 

 variable in the test, because the tools were operated until they broke down. 



The milling cutters for the selective test of carbon tool steel, classes i 

 and 2, are shown on sheet No. 1058, Plate 142. These cutters were operated 

 until they broke down either in the shank or teeth. The elapsed time of 

 run of the cutters was recorded and represents the total time the cutters 

 were operating, but does not include the time required to return the milling 

 machine table to the starting point and to set for the next cut. The selective 

 factor represents the ratio of the mean elapsed time of run of all cutters of 

 one sample to the price per pound of that sample. 



