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1. Teaching Week 03:
Keys & Keyways

2. Outline
- What is a key & keyway?
- Why do we need keys & keyways?
- How does the selection of a key & keyway fit into
the design process?
- Methodology
- Example
- Conclusions / Wrapping up

3. What is a key & keyway?
Types of keys
Key
Machine component (machine element) used to keep two other machine
components together (e.g. to mount a gear or pulley onto a rotatingshaft)
Clarification:
shaft keys (or sunk keys):
machine elements that transmit
torque between shafts and shaft-
mounted components such as
gears or pulleys
Typical key & keyway arrangement

4. Axial centric load
σ: averagevalue
of stressovercross
sectional areaA
Shear
Opposingtransverse
loads(shearingforces)
creatingshearon
memberAB
τ: average shearing
stress in sectionA
A
(a) (b)
(a)Memberwithanaxial loadP;
(b)Idealized uniformstressdistributionatan
arbitrarysection

5. Stress on an Oblique Plane
• Passasectionthroughthememberat anangleθ
withthenormalplane
• Forceequilibrium:distributedforcesonoblique
planemust beequivalent toforceP
• ResolvePintocomponentsnormaland
tangential toobliquesection
F  Pcos V  Psin
• Theaveragenormal andshearstressesonthe
obliqueplaneare:

6. • Maximumnormal stress:referenceplane
perpendiculartomemberaxis
• Maximumshearingstress:for aplaneat +45o
withrespecttotheaxis&equaltohalfofσm
Maximum Stresses
• Normalandshearingstressesonobliqueplane:

7. Typical key & keyway configuration
T
ypical application of
forcesonakey
r = D/2
r: radius of shaft
D: diameter of shaft

8. Forceappliedbyshaft tokey Forceappliedbypulleytokey
Keys and keyways (BS 4235-1:1972)

9. σ: compressive (normal) stress
σallowable: allowable value for σ
σy: yieldstress
T
:torqueon shaft
h: keyheight
L: keylength
F
.O.S.:Factor of Safety
Keys and keyways (BS 4235-1:1972)

10. Keys and keyways (BS 4235-1:1972)
τ: shearing(tangential) stress
σ: compressive(normal) stress
σallowable:allowablevaluefor σ
σy: yieldstress
T
:torqueon shaft
b:keywidth
L:keylength
F
.O.S.:Factor of Safety

11. Should the height or the width of a key be larger
and why?
Strength
against
shear
Strength
against
compression
“Keys are generally designed to fail before overloads can cause damage to the shaft
or attached component”. Is this statement correct or not and why?

12. Keys and keyways (BS 4235-1:1972)
Definition of geometry for square parallel keys

13. Keys and keyways (BS 4235-1:1972)
Table with dimensions & tolerances for square parallel keys

14. Keys and keyways (BS 4235-1:1972)
Definition of geometry for rectangular parallel keys

15. Keys and keyways (BS 4235-1:1972)
Table with dimensions & tolerances for rectangular parallel keys