Orthogonal-cutting experiments using SAE 1112 free-cutting steel, 2024-T4 and 6061-T6 aluminum alloys, and alpha-brass (85 Cu-15 Zn) at feeds of 0.002 to 0.010 ipr, were performed on a lathe with 18-4-1 high-speed-steel cutting tools. The mean cutting speeds and rake angles for SAE 1112 varied from 33.7 to 170.8 fpm and 5 to 40 deg, respectively, while the remainder of the alloys were tested at conditions yielding a continuous chip without a built-up edge at speeds ranging from approximately 470 to 790 fpm. It was found that the angle λ between the shear plane and the resultant tool force R was only approximately constant for each test condition and varied with cutting speed. Hence the equation λ = ϕ + β − α = const and the linear relationship between ϕ and β − α are only approximately satisfied. Furthermore, neither the Ernst and Merchant minimum-energy criterion, nor the Lee and Shaffer nor the Hill ideal plastic-solid solution, is in agreement with all the experimental observations.

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