Project # 2  Slides
Shaft Design
Step # 1  Determine the conceptual shape/design of each of the two shafts
Step # 2  Select Materials for the Shafts
Assume the basic shaft diameters and make a first trial material selection for each shaft
Hint: For strength based designs, shafts having diameters less than 3.5" are usually made from a cold drawn steel in order to resist fatigue
Hence,
For D £ 3.5" Cold Drawn (CD) Material  better surface finish and easily machinable
For D ³ 3.5" Hot Rolled (HR) or preferably Quenched & Treated (Q&T)  generally rough surface but low cost
Step # 3  Select safety factors for the design of each shaft
Basic Rules:
Safety Factor 
Condition/Case 
2 
For ductile materials where a high level of confidence exists in the loads, material properties and operating conditions 
3 
For brittle materials where a high level of confidence exists and operating conditions are well known 
3 
For ductile materials with some doubt about the adequacy of material properties data, loads or the stress analysis 
4 
For uncertain conditions about same combination of material properties, loads and the stress analysis 
Step # 4  Calculate the torques and sketch torque diagrams for each shaft
Using the following equation, calculate the torque of each shaft:
T=63000*P/n  lb.in. 

Draw the torque diagrams based upon the torque values
Step # 5  Determine the tangential and normal forces on each of the gears
Tangential Force:
W_{t} = T/(D/2) compute for G_{1}, P_{2} and G_{2}
Radial Force:
W_{r} = W_{t} (Tan F ) compute for G_{1}, P_{2} and G_{2}
Where: F (Pressure angle) is 20°
T is torque
D is gear pitch diameter
Step # 6  Perform a complete force analysis for each shaft and draw force diagrams showing all forces acting on the shaft and compute the bearing reactions at the bearing seat locations
Resultant reaction at any point is given by:
R=square root(R_{y}^{2}+R_{z}^{2})
Step # 7  Draw shear force and bending moment diagrams for the shafts, both in the vertical and horizontal planes and draw the resultant bending moment diagrams
Do the following for each shaft:
Step # 8  Determine the basic shaft diameters using static analyses and rough assumptions
Do the following for each shaft:
Step # 9  Determine the shaft diameters using fatigue analyses
Do the following for each shaft: