TOOL STEEL FOR THE UNITED STATES NAVY. 347 



intended, of the tool steels offered by the bidders, and the recommendation 

 for award of contract was based on the information thus obtained. In 

 order to obtain samples of tool steel for the selective test the specifications 

 required each bidder to furnish a sample bar of the tool steel he offered; 

 and this sample bar was delivered to the engineer officer for him to direct 

 the selective test. The heat treatment of the tools, their chemical analy- 

 sis, the conditions of the physical test, and the computations necessary to 

 determine the award of contract constitute the selective test. A lathe tool 

 selected for the physical test was kept cutting, without lubricant, until 

 it failed by the sudden breaking down of the cutting edge due to heating 

 caused by the friction of the chip; and a record of the elapsed time of run, 

 or cutting life of the tool, was made. By keeping the other conditions con- 

 stant the elapsed time of run was the principal variable. Each tool after 

 failure was reground, care being taken to remove the effects of the heating 

 due to the previous cut, and again tested until the tool broke down as 

 above described, after which it was reground and tested a third time. 



It was considered that the cutting life, as shown by the elapsed time of 

 run above described, and the cost of the material were the principal factors 

 in determining a selection, because the number of times the tools could be 

 reforged and reground, and the cost of keeping them in efficient condition, 

 would be practically the same regardless of the quality of the tool steel. 

 Therefore the ratio of the arithmetical mean of the elapsed time of all runs 

 of the tools of one sample to the price per pound of the material was com- 

 puted. It was recommended that the contract be awarded for the purchase 

 of the tool steel of highest "ratio. " The data of this selective test are given 

 on sheet No. 607, Plate 141. 



An estimate was made to determine the relative values of the several 

 tool steels tested by computing, first, the value for each sample which would 

 give it a "ratio" equal to the highest "ratio," and second, to determine 

 the value of the tool steel of highest ratio to obtain a ratio equal to that of 

 each sample. The values thus computed are given on sheet No. 607, 

 Plate 141. 



A test under the conditions prevailing during the above selective test 

 was made of tool steel which had been purchased under specifications, 

 Appendix A, from four contractors in order to learn if it were equal or superior 

 to the commercial tool steels which had just been subjected to a selective 

 test ; and it proved conclusively that some of the commercial tool steels were 

 superior. The data of this test are given on sheet No. 607, Plate 141. 



Schedule jSgj. — The information obtained from the selective test under 

 Schedule 3244 indicated that it was advisable again to revise the specifica- 



