Key: A machine element used to removably join machine parts, such as gears, pulleys, or couplings, to shafts, and to transmit motion on the shaft.
They act as an intermediary for transferring rotary motion from the shaft to the machine parts. They’re elements that allow disassembly and reassembly while also providing a secure connection.
The handwheel used on machine tools like lathes and milling machines is also an example of a keyed connection. (above)
In keyed connections, a keyway is cut into the hub of machine parts like pulleys, flywheels, or gears. Likewise, a keyway is also cut into the shaft we want to join it to. (above)
Joining the shaft and pulley with a key (above)
The key is assembled so that half of it sits in the keyway cut into the shaft, and the other half sits in the keyway cut into the part being joined.
The shaft is inserted into the pulley’s hub, and the part called the key is placed into the keyway.
This type of connection provides a joint that can be disassembled whenever needed, while also having the key absorb the forces coming onto the shaft during load transmission. This way, if something has to break over time, it’s the key that breaks, sparing the shaft or the pulley from damage.
Keys create a link between the shaft and the hub, allowing force or motion to pass from the shaft to the hub, or from the hub to the shaft. This way, the shaft and hub become a single unit and rotate together to do work.
How Keys Are Shown in Technical Drawings
When keys are shown in a technical drawing, the clearance between the key and the keyway normally isn’t visible to the eye. However, this clearance is indicated in the drawing.
The key isn’t hatched when a section is taken. If it’s a tapered key, this taper amount is indicated. (image above)
Key Material
Making a keyway is harder and more costly than making a key. Because of this, it’s preferred for the key to fail rather than the keyway. For this reason, keys need to be made of a softer material than the machine parts being joined.
Connecting keys are usually made from steels with a tensile strength of 40-60 kg/mm2.
Standard Designation of Keys:
When ordering parallel keys, the order is placed by specifying the key name, dimensions, and TS (Turkish Standard) number.
For example: the designation for a gib head key with a width of b = 16, a height of h = 10, and a length of l = 180 mm is =
Gib head key 16x10x180 TS147/6
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