5 - KEYS AND COUPLINGS DESIGN ME 418
TOPIC NO. 5
KEYS and COUPLINGS DESIGN
Flat Key – rectangular key with the smaller
This topic includes the following:
dimension placed in a radial direction
5.1 Flat and square keys relative to the shaft.
5.2 Flexible coupling
Square Key – key with a square section.
Gibhead Key - a square or flat tapered key
Key – a machine member used to connect
with a head for ease in removal.
two mating pairs (usually a shaft to a pulley,
gear, coupling, etc.) such that relative Pin Key – key of round section; sometimes
motion is prevented between them. used as a shear pin.
Keyway – a groove at the mating members
where the key fits.
Spline – permanent keys made integral with
the shaft.
Types of Keys:
Rollpin – a hollow round key with a split to
produce flexibility along its circumference
when inserted into the keyway.
Saddle Key – a flat key with its bottom side
having a radius of curvature slightly less that
of the shaft radius. This is a friction
dependent key and thus, its torque capacity
is minimal.
Kennedy keys – two square keys that are 90°
apart whose diagonals coincide with the
shaft circumference.
MACHINE DESIGN 1 Page 1
, 5 - KEYS AND COUPLINGS DESIGN ME 418
Woodruff Key – key that fits into a semi- Compression of key
cylindrical seat at the shaft. Since it goes
deeper into the shaft, it has a less tendency
to tip when the load is applied.
Feather key – a long flat key that allows the
hub to move along the shaft, but prevents
rotation on the shaft.
Barth key - a flat key with beveled bottom 𝐹
𝑆𝑐 = = 𝑆𝑑 ∶ 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 2
corners. 1
( ) 𝑡𝐿
2
Stress Analysis
Where:
L= length of key
B= width
T= thickness
F= force applied
Ss= shearing stress
Sc= compressive stress or bearing
stress
2𝑇
𝐹=
𝐷 Ssd= shear design stress
Sd= normal design stress
Shearing of key:
Note:
The required key length is computed
from each of equations 1 and 2. Use
whichever is longer!
𝐹
𝑆𝑠 = = 𝑆𝑠𝑑 ∶ 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 1
𝑏𝐿
MACHINE DESIGN 1 Page 2
TOPIC NO. 5
KEYS and COUPLINGS DESIGN
Flat Key – rectangular key with the smaller
This topic includes the following:
dimension placed in a radial direction
5.1 Flat and square keys relative to the shaft.
5.2 Flexible coupling
Square Key – key with a square section.
Gibhead Key - a square or flat tapered key
Key – a machine member used to connect
with a head for ease in removal.
two mating pairs (usually a shaft to a pulley,
gear, coupling, etc.) such that relative Pin Key – key of round section; sometimes
motion is prevented between them. used as a shear pin.
Keyway – a groove at the mating members
where the key fits.
Spline – permanent keys made integral with
the shaft.
Types of Keys:
Rollpin – a hollow round key with a split to
produce flexibility along its circumference
when inserted into the keyway.
Saddle Key – a flat key with its bottom side
having a radius of curvature slightly less that
of the shaft radius. This is a friction
dependent key and thus, its torque capacity
is minimal.
Kennedy keys – two square keys that are 90°
apart whose diagonals coincide with the
shaft circumference.
MACHINE DESIGN 1 Page 1
, 5 - KEYS AND COUPLINGS DESIGN ME 418
Woodruff Key – key that fits into a semi- Compression of key
cylindrical seat at the shaft. Since it goes
deeper into the shaft, it has a less tendency
to tip when the load is applied.
Feather key – a long flat key that allows the
hub to move along the shaft, but prevents
rotation on the shaft.
Barth key - a flat key with beveled bottom 𝐹
𝑆𝑐 = = 𝑆𝑑 ∶ 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 2
corners. 1
( ) 𝑡𝐿
2
Stress Analysis
Where:
L= length of key
B= width
T= thickness
F= force applied
Ss= shearing stress
Sc= compressive stress or bearing
stress
2𝑇
𝐹=
𝐷 Ssd= shear design stress
Sd= normal design stress
Shearing of key:
Note:
The required key length is computed
from each of equations 1 and 2. Use
whichever is longer!
𝐹
𝑆𝑠 = = 𝑆𝑠𝑑 ∶ 𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 1
𝑏𝐿
MACHINE DESIGN 1 Page 2
