The section of shaft shown in the figure is to be designed to approximate relative sizes of d = 0.75D and r = D/20 with diameter d conforming to that of standard metric rolling-bearing bore sizes. The shaft is to be made of SAE 2340 steel, heat-treated to obtain minimum strengths in the shoulder area of 1207 MPa ultimate tensile strength and 1103 MPa yield strength with a Brinell hardness not less than 370. At the shoulder the shaft is subjected to a completely reversed bending moment of 67.8 N-m, accompanied by a steady torsion of 45.2 N-m Use a design factor of 2.5 and size the shaft for an infinite life.
Section of a shaft containing a grinding relief groove with radius r is shown. The diameter at the root of the groove is, dr = d – 2.r, and though the section of diameter d is ground, the root of the groove still a machined surface.