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In this paper a method is described for testing lathe tools under shallow cuts and fine feeds. The relations are determined between the cutting speed, feed, depth of cut, and tool life for carbon and high-speed tool steels. Comparisons are made of tools of different forms and of tool life when cutting dry and with water or lard oil. Heat treatment and chemical composition of the tools are also studied, including in the case of high-speed tool steels, the effects of cobalt, nickel, molybdenum, arsenic, antimony, phosphorus, sulphur, copper, tin, aluminum, titanium, and tantalum. The results obtained under shallow cuts and fine feeds with these steels are compared with those obtained under heavy duty.

This investigation was made for the purpose of developing a method of testing cemented-tungsten-carbide lathe tools under heavy duty and to extend to the new cutting material some of the laws originally developed by Taylor and his associates for cutting with carbon- and high-speed-steel tools. Relations were determined between the speed, feed, depth of cut, and tool life for a selected form and size of tool. All tests were made dry in cutting 3.5 per cent nickel-steel forgings, heat-treated to give tensile strengths within the range of 85,000 to 110,000 lb. per sq. in. The results are presented in both graphic and tabular forms.

Tests described in this report extend portions of Taylor’s original investigations in rough turning carbon steels to current commercial high-speed tool and structural alloy steels. They were made primarily to show the effect upon tool performance of variation in chemical composition and mechanical properties of the steel cut, and accordingly include lathe tests on carbon, nickel, low- and high-chromium, chromium-vanadium, chromium-molybdenum, and nickel-chromium steels having tensile strengths between 65,000 and 195,000 lb. per sq. in. However, many of the tests with the customary high-tungsten-low-vanadium steel tools were duplicated with low-tungsten-high-vanadium or cobalt high-speed steel tools, and there is included a partial study of the effects of cutting speed, feed, depth of cut, and coolants upon tool life and the power required in cutting. Graphical representation of results is employed, wherever possible, to show the laws of cutting.

The tests described in this report were made primarily as a study of lathe-tool performance with shallow cuts as affected by variations in chemical composition and heat treatment of the steels cut. The cutting tests were made dry with high-speed-steel tools of a selected size, form, composition, and heat treatment, with a feed of 0.0115 in. per rev. and 0.010 in. depth of cut. Comparisons were made of the Taylor speeds on the basis of equal tensile strengths when cutting 0.4 per cent carbon (S.A.E. 1040), chromium-vanadium (S.A.E. 6140), nickel-chromium (S.A.E. 3140 and 3435), chromium-molybdenum (S.A.E. 4140), and 3½ per cent nickel (S.A.E. 2340) steel forgings heat treated to give tensile strengths between 75,000 and 220,000 lb. per sq. in. The study also included consideration of the surface finishes of the various steel forgings as affected by the test conditions, the microstructures of the steels cut, and tool performance as affected by the additions of 3.5 to 11.7 per cent cobalt to the customary 18 per cent tungsten type of high-speed tool steel. If machinability is measured by the cutting speed permitting the tools to last a definite time, then measurable differences were observed between the various steels cut in the lathe test with shallow cuts. The fact, however, that some given steel permits a higher cutting speed than another steel for some tensile strength which is the same for both materials does not necessarily indicate that the two steels maintain the same relationship for another tensile strength. Of the different steels cut in the lathe tests, the plain carbon steel was the most difficult to machine other than an annealed nickel-chromium steel. The surface finish on the plain carbon steel was also considered to be inferior to the surface finish of the alloy steels. The results showed that the effect of changes in chemical composition of steel forgings upon their cutting speeds was dependent upon the tensile strength at which the comparisons were made. In the different steels cut with shallow cuts the most effective special alloying elements for improving machinability were the combinations of nickel and chromium or chromium and vanadium for the high tensile strengths in the neighborhood of 180,000 lb. per sq. in., while chromium and molybdenum were the most effective in the lower range of about 90,000 lb. per sq. in.