The following procedure may be adopted for designing a crankshaft.
1. First of all, find the magnitude of the various loads on the crankshaft.
2. Determine the distances between the supports and their position with respect to the loads.
3. For the sake of simplicity and also for safety, the shaft is considered to be supported at the
centres of the bearings and all the forces and reactions to be acting at these points. The distances
between the supports depend on the length of the bearings, which in turn depend on the diameter of
the shaft because of the allowable bearing pressures.
4. The thickness of the cheeks or webs is assumed to be from 0.4 ds to 0.6 ds, where ds is the
diameter of the shaft. It may also be taken as 0.22D to 0.32 D, where D is the bore of cylinder in mm.
5. Now calculate the distances between the supports.
6. Assuming the allowable bending and shear stresses, determine the main dimensions of the
crankshaft.
Notes: 1. The crankshaft must be designed or checked for at least two crank positions. Firstly, when the crankshaft
is subjected to maximum bending moment and secondly when the crankshaft is subjected to maximum
twisting moment or torque.
2. The additional moment due to weight of flywheel, belt tension and other forces must be considered.
3. It is assumed that the effect of bending moment does not exceed two bearings between which a force is
considered.
FIRST MULTICOLOUR EDITION
(S.I. UNITS)
[A Textbook for the Students of B.E. / B.Tech.,
U.P.S.C. (Engg. Services); Section ‘B’ of A.M.I.E. (I)]
A TEXTBOOK OF
Machine Design
R.S. KHURMI
J.K. GUPTA
(S.I. UNITS)
[A Textbook for the Students of B.E. / B.Tech.,
U.P.S.C. (Engg. Services); Section ‘B’ of A.M.I.E. (I)]
A TEXTBOOK OF
Machine Design
R.S. KHURMI
J.K. GUPTA