348 TOOL STEEL FOR THE UNITED STATES NAVY. 



tions for the following reasons : — First, to more clearly explain the require- 

 ments to the bidders, and second, to utilize the information obtained in 

 preparing more rigid specifications. 



The analyses of the sample bars submitted under Schedule 3244 were 

 utilized in preparing the chemical compositions for the specifications, and 

 the limits of the elements were made broad enough to include the best grades 

 of "high speed" tool steel. For purposes of classification, the "high speed" 

 tool steel was designed as tungsten tool steel, class i , in the specifications. 



These specifications, which are given in Appendix C, required a selective 

 test similar in character to that previously described. The purposes for 

 which the tool steels are, in general, adapted was inserted in the specifications 

 to assist navy yards in selecting tool steels adapted to their needs, and also 

 as a guide for bidders in case they should desire to submit, for selective test, 

 tool steels of a composition differing from that specified. The conditions 

 throughout the selective test were kept as nearly uniform as facilities would 

 permit so that the principal variable was the elapsed time of run, or cutting 

 life of the tool. With all the care exercised, variations in the elapsed time of 

 run occurred for each sample, and, in order to determine if any of the obser- 

 vations of the elapsed time of run should be rejected, they were adjusted by 

 the principles of least squares. 



During this test a volt meter and ammeter were used to determine the 

 input to the motor which drove the test lathe, in order to obtain a measure 

 of the work done by the nose of the tool. The ammeter readings varied for 

 the different tools, due principally to slight variations in depth of cut and 

 cutting speed, which indicated that the work done by the different tools was 

 not the same, and in order to allow for this difference in computing the 

 selective factor a quantity was introduced called "work value," which is 

 the product of the mean elapsed time of run of all tools of one sample and 

 the mean watts required to drive the lathe minus the friction watts. The 

 work value, therefore, is the watt-minutes of work done by the tool. 



The "work value" divided by the price per pound of the material gave 

 the selective factor for this test. The relative values of the tools steels were 

 computed as previously described, and the data of this test, together with 

 the chemical analyses of the tool steels, are given on sheet No. 1058, Plate 142, 



Schedule 4469. — Another revision of the specifications was considered 

 necessary after the above selective test had been completed, in order that 

 advantage might be taken of the additional information obtained, and the 

 feature of a selective test was continued. The new specifications are given 

 in Appendix D. 



The selective test was conducted under uniform conditions as previously 

 described, so that the principal variable was the elapsed time of run of the 



