Question

A gear and shaft with nominal diameter of 34 mm are to be assembled with a medium drive fit (H7/s6). The gear has a hub, with an outside diameter of 45 mm, and an overall length of 50 mm. The shaft is made from AISI 1020 CD steel, and the gear is made from steel that has been through hardened to provide Su = 700 MPa and Sy = 600 MPa. a) Specify dimensions with tolerances for the shaft and gear bore to achieve the desired fit. b) Determine the minimum and maximum pressures that could be experienced at the interfaces with the specified tolerances. c) Determine the worst-case static factors of safety guarding against yielding at assembly for the shaft and the gear based on Von-Mises failure theory. d) Determine the maximum torque that the joint should be expected to transmit without slipping.

Answer 1

Dimensions for medium drive fit H7/s6 involve specific tolerance ranges for the gear bore and shaft. Calculations for minimum and maximum pressures, static safety factor using Von-Mises criterion, and the maximum torque require additional mechanical formulae and data on material properties and fits.

Step-by-step explanation:

Specifications for Shaft and Gear Bore for Medium Drive Fit (H7/s6)

To achieve a medium drive fit specified as H7/s6 for a 34 mm nominal diameter gear and shaft: The gear bore tolerance should fall under the H7 category, which allows a range of +0mm to +25μm for diameters between 30mm and 50mm. The shaft tolerance should be within the s6 category, specifying a range of -18μm to -43μm for a nominal diameter of 34 mm.

Minimum and Maximum Interface Pressures

The minimum interference will occur when the upper limit of the gear bore size coincides with the lower limit of the shaft size. Conversely, maximum interference will occur when the gear bore is at its lower limit and the shaft at its upper limit.

Worst-Case Static Safety Factor

The worst-case static safety factor guarding against yielding using Von-Mises failure theory will be calculated by comparing the Von-Mises stress induced during the assembly to the yield strength of the materials of both the gear and the shaft.

Maximum Torque Without Slipping

The maximum torque that the assembled joint should transmit without slipping will depend on the coefficient of friction, fit quality, and the forces experienced during assembly.