Keys

Key
• Key a key is a small piece of metal used to transmit torque from a rotating
shaft to a component that slides or rotates on the shaft.
• The key fits into a corresponding slot, known as a keyway, which is
machined into both the shaft and the component.
• The key prevents relative motion between the shaft and the component,
ensuring that torque is efficiently transmitted.
Keyway
• A keyway is a slot or groove that is machined
into a shaft or component to receive a key.
• The keyway is usually cut along the length of the
shaft or component and is designed to match
the shape and size of the key.
• The keyway ensures that the key fits securely
and snugly into the shaft, preventing any
relative motion between the shaft and the
component.
Types of keys
• A square key is a type of key that has a square cross-section and is
commonly used to transmit torque between a rotating shaft and a
component that slides or rotates on the shaft.
• The key fits into a keyway, which is a slot cut into the shaft and the
component, preventing relative motion between them.
• The square key is popular in low to medium power transmission
applications due to its simple design and ease of manufacturing.
Types of keys
• A flat key is a type of key that has a
rectangular cross-section and is used to
connect a rotating shaft and a component
that slides or rotates on the shaft.
• Flat keys are used for transmitting torque in
low to medium power applications.
• They are commonly used in milling machines,
lathes, and other power transmission
equipment.
Types of keys
• A round key is a type of key that has a
circular cross-section and is used to
transmit torque between a rotating shaft
and a component that slides or rotates on
the shaft.
• Round keys are commonly used in high
power applications because they can
transmit torque more efficiently than other
key types.
Types of keys
• A Barth key is a type of key that has a
trapezoidal cross-section and is commonly
used in applications where high torque
transmission is required.
• The key fits into a matching keyway, which is
cut into the shaft and the component,
ensuring that the two remain in place relative
to each other.
Types of keys
• A Woodruff key is a type of key that has a semi-circular cross-section
and is commonly used to secure gears, pulleys, and other components
to a shaft.
• The keyway is cut into the shaft in the form of a semicircle, while the
Woodruff key is shaped to fit the keyway.
Types of keys
• A Gib-head taper key is a type of key that has a tapered cross-section
and is commonly used in machine tool applications.
• The taper allows for easy insertion and removal of the key, while the
gib-head prevents the key from moving axially.
Types of keys
• A feather key is a type of key that has a trapezoidal cross-section and is
commonly used in applications where a high degree of accuracy is
required.
• The key fits into a matching keyway, which is cut into the shaft and the
component, preventing relative motion between them.
• The feather key is popular in machine tool and automotive applications.
Types of keys
• A saddle key is a type of key that has a
saddle-shaped cross-section and is
commonly used in applications where
the shaft and the component need to be
easily assembled and disassembled.
• The saddle key fits into a matching
keyway, which is cut into the shaft and
the component.
Types of keys
• A Kennedy key are tapered square keys with the diagonal dimension is a
circumferential direction
 Types of keys
Key Type Cross-SectionCommon Applications Keyway Type Advantages Disadvantages
Low to medium power
Square key Square Rectangular Simple design, easy to manufacture May cause stress concentrations
transmission
Low to medium power
Flat key Rectangular Rectangular Widely available, simple to manufacture Can slip out of place under high loads
transmission
High power
Round key Circular Circular Transmits high torque efficiently Difficult to manufacture, can be expensive
transmission
High torque Requires matching trapezoidal keyway,
Barth key Trapezoidal Trapezoidal Can handle high loads and torque
transmission limited availability
Securing gears, pulleys,
Woodruff key Semi-circular Semi-circular Does not require a keyway, self-aligning Limited torque transmission capacity
etc.
Rectangular
Gib-head Machine tool Easy to insert and remove, can handle high Requires matching tapered keyway, can
Tapered with tapered
taper key applications loads cause stress concentrations
end
Easy assembly and
Saddle key Saddle-shaped Rectangular Easy to assemble and disassemble Limited torque transmission capacity
disassembly
Square with Provides high torque transmission, easy to Requires matching hexagonal keyway,
Kennedy key Square Marine applications
tapered end insert and remove limited availability
Provides accurate alignment, can handle Requires matching keyway, limited
Feather key Trapezoidal High accuracy required Rectangular
high loads availability
Rectangular High torque keyway Limited to specific shaft and hub
Splines Can transmit high torque
with teeth transmission broached hub combinations, difficult to manufacture
Stresses in Square and Flat Keys
Stresses in Round Keys
Square and Rectangular key Sizes
• Square keys are most common for shafts
up to 6/12 in. in diameter
• Rectangular keys are recommended for
larger shafts and smaller shafts where
shorter height is tolerable
• Table 11-1 gives preferred dimensions for
parallel keys based on shaft diameter for
U.S. and SI Metric sizes.
Materials for keys
• Keys can be made from carbon steel, alloy
steel, stainless steel, nonferrous metals,
and even plastics.
• For most applications, low-carbon steel
SAE 1018 is recommended due to its low
cost, availability, and adequate strength.
• High-carbon steel SAE 1095 may be used
but may have low ductility.
• Stainless steels are suitable for keys where
corrosion resistance is necessary.
• Aluminum 6061 is less frequently used but For higher strength requirements, medium-
may be desirable for material
carbon steels SAE 1035 or 1045, or alloy
compatibility reasons.
steels SAE 4140 or 8630 are recommended.
DESIGN PROCEDURE FOR PARALLEL KEYS

1. Specify the shaft diameter at the keyseat

2. Select the key size from Table 11-1
3. Specify the design factor, N (typically N = 3)
4. Specify key material (SAE 1018 steel is
common)
5. Determine yield strength of key, shaft, and
hub materials
6. Compute minimum required length of key
7. Specify actual key length to be equal to or
longer than computed minimum
A UNS G10350 steel shaft, heat-treated to a minimum yield strength of 75 kpsi, has a diameter
of 1 7/16 in. The shaft rotates at 600 rev/min and transmits 40 hp through a gear. Select an
appropriate key for the gear.
,
A UNS G10350 steel shaft, heat-treated to a minimum yield strength of 75 kpsi, has a diameter
of 1 7/16 in. The shaft rotates at 600 rev/min and transmits 40 hp through a gear. Select an
appropriate key for the gear.
The pump operates using the motor that has a power of 85 W. If the diameter
transmission shaft is 20-mm- Specify the recommended key size.

W = 6 mm,
H = 6 mm
A keyed gears deliver a torque of 912.4 N-m who is Shaft of 63.5 mm outside diameter. If the
key has thickness 15.875 mm and width of 11.1125 mm, find the length of the key. Assume
the permissible stress value of 61.2 Mpa for shear and tension at 99.8 MPa.
A belt pulley used to drive a device is attached to a 30-mm-diameter shaftwith a square shear
key. The belt tensions are 1,500 N and 600 N, as shown. The shear key dimensions are 6 mm
by 6 mm by 25 mm long. Determine the shear stress produced in the shear key.

𝟐
Determine the required key geometry: length, width, and height. Use SAE 1018 steel for the
keys if a satisfactory design can be achieved. If not, use a higher-strength material from Table
11–4. Unless otherwise stated, assume that the key material is weakest when compared
with the shaft material or the mating elements. Specify a key for a gear to be mounted on a
shaft with a 2.00 in diameter. The gear transmits 21,000 lb-in of torque and has a hub length
of 4.00 in.
Determine the required key geometry: length, width, and height. Use SAE 1018 steel for the
keys if a satisfactory design can be achieved. If not, use a higher-strength material from Table
11–4. Unless otherwise stated, assume that the key material is weakest when compared
with the shaft material or the mating elements. Specify a key for a gear to be mounted on a
shaft with a 2.00 in diameter. The gear transmits 21,000 lb-in of torque and has a hub length
of 4.00 in.
Determine the required key geometry: length, width, and height. Use SAE 1018 steel for the
keys if a satisfactory design can be achieved. If not, use a higher-strength material from Table
11–4. Unless otherwise stated, assume that the key material is weakest when compared
with the shaft material or the mating elements. Specify a key for a gear to be mounted on a
shaft with a 2.00 in diameter. The gear transmits 21,000 lb-in of torque and has a hub length
of 4.00 in.
Determine the required key geometry: length, width, and height. Use SAE 1018 steel for the
keys if a satisfactory design can be achieved. If not, use a higher-strength material from Table
11–4. Unless otherwise stated, assume that the key material is weakest when compared
with the shaft material or the mating elements. Specify a key for a gear to be mounted on a
shaft with a 2.00 in diameter. The gear transmits 21,000 lb-in of torque and has a hub length
of 4.00 in.