This document discusses shafts, keys, and couplings used for power transmission. It describes the different types of shafts including transmission shafts, stepped shafts, and hollow shafts. Common shaft materials are listed as well as standard shaft sizes. Equations are provided for calculating stresses induced in shafts from torsion, bending moments, and axial thrust. Different shaft failure cases are outlined. Key types are defined including sunk, saddle, and woodruff keys. Guidelines for designing sunk keys are also mentioned.

1. Shafts, Keys and Couplings

2. Shafts
• Transmission Shafts
– Rotating machine elements, circular in
cross section, supporting transmission
elements like gears, pulleys and
sprockets and transmit power

3. Transmission Shaft
Stepped Shaft
Fillets
Keyways
Journals
Hollow shafts: Reduced weight,
Facilitates shaft-in-shaft

4. Different names depending on
application
• Axle
• Spindle
• Countershaft
• Line-shaft

5. Shaft Material
• Medium Carbon Steel 0.15 to 0.40% C
• High Carbon Steel for greater strength
• Alloy Steels – Ni, Cr, Mo as alloying elements

6. Standard Sizes
5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 25,
28, 30, 32, 35, 40, 45, 50, 55, 60, 65,
70, 75, 80, . . .

7. Shaft Design – Strength Basis
Shafts may be subjected to Torsion, Bending
Moment or Axial Thrust and their
combination
Most shafts are subjected to combined
Bending Moment and Torsion
Axles are subjected to Bending Moment

8. Stresses induced
• Due to Torsion
• Due to Bending Moment
• Due to axial thrust 2
4
D
P P
A d


 
3
16
T T
r
J d


 
3
32
B
M M
y
I d


 

9. Different cases
• Torsion and Bending (τ and σB)
• Torsion and Thrust (τ and σD)
• Torsion, Bending and Thrust (τ, σB and σD)
y,S
2 2
S
1
4 ,
2 N
Max B Max
   
  
y,S
2 2
S
1
4 ,
2 N
Max D Max
   
  
y,S
2 2
,
S
1
4 ,
2 N
B D Max Max
      
    

10. ASME Code for Shaft Design
According to this code
Whichever is less (If no keyway. In presence of
keyway, these values are to be reduced by
25%)
The values of torque T and Bending moment M
are to be multiplied by factors kt and km to
account for shock and fatigue
, ,
0.30 or 0.18
Max y t Max U t
S S
 
 

11.    
2 2
3
16
Max b t
k M k T
d


 
Values of kb and kt are specified by the
code, depending on different service
conditions

12. Factors kb and kt
Service kb kt
Loads gradually
applied
1.5 1.0
Loads suddenly
applied (Minor
shock)
1.5 – 2.0 1.0 – 1.5
Loads suddenly
applied (Major
shock)
2.0 – 3.0 1.5 – 3.0

13. Keys
• Machine elements to connect
transmission shaft to rotating elements
like pulley, gear, flywheel and sprocket
• Keyways are cut on the shaft and the hub
of rotating element

14. Types of Keys
1) Sunk : a) Flat or Rectangular b) Square
c) Gib Headed d) Feather e) Woodruff
2) Saddle
3) Tangent
4) Round Keys and Taper pins
5) Kennedy
6) Splines

15. •Saddle key : Light duty Appl.
full key in hub,
avoids shaft weakening
•Sunk keys
Half key in shaft

16. Keys - Types
• Gib-headed taper key – Taper 1:100
• Woodruff key

17. Keyway on a shaft

18. Design of a sunk key
Practice to use b = h = d/4 (SQ.); l = 1.5d
b = d/4 & h = d/6 (Rect.); l = 1.5d
2 / ;
2 4 2
=
C
P T d
P T P T
hl dhl bl dbl
 

  
d = shaft diameter h = key height
b = key width l = key length

19. THANK YOU