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A.  SHAFTS

1.0 INTRODUCTION
Shafts are used to transmit motion, torque and/or power in any combination.They are also subject
to lateral loads. These can be constant or fluctuating. The sizing of shafts, therefore, is usually determined as a function of torsionally Induced stresses (shear stresses), bending stresses (tensile or compressive stresses) and the nature of the load (constant or fluctuating).

2.0 DETERMINATION OF STRESSES FOR SOLID CYLINDRICAL SHAFTS

(a) Nomenclature
Let          d = shaft diameter, in.
          H.P. = horsepower
            K_m = shock factor for bending loads
             K_t = shock factor for torsional loads
             M = bending moment, In-lbs.
             N = revolutions per minute (RPM)
              S = shear stress, lbs/inē
        S_max = maximum allowable shear stress, lbs/inē
              T = torque, in-lbs.
        T_max = maximum allowable torque, In-lbs.

(b)  Relation Between Torque and Horsepower
          T = 63,025 (H.P.)                                                                                                    (1)
                         N

(c) Torsional Loading
For shafts under steady torsional loads (and no bending loads),

d =   (5.09 T)^1/3                                                                                                                  (2)
          S                    
   In the particular case of a shaft in which S_max = 12,000 psi (for example in the case of #303 stainless steel and a gradually applied load), equations (1) and (2) can be combined to yield:

T_max = 2353 d³                                                                                                                  (3)
and
(H.P.)_max = 0.037 d³N                                                                                                       (4)

   Table 1 shows maximum safe torsional loads based on #303 stainless steel with S_max = 12,000
psi and a gradually applied load:

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