Keyway (engineering)
Encyclopedia
In mechanical engineering
Mechanical engineering
Mechanical engineering is a discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the production and usage of heat and mechanical power for the...

, a key is a machine element
Machine element
Machine elements are basic mechanical parts used as the building blocks of most machines. Most are standardized to common sizes, but customs are also common for specialized applications.-Types:*Shafts**Couplings*Keys*Splines*Bearings**Roller bearings...

 used to connect a rotating machine element to a shaft. Through this connection the key prevents relative rotation between the two parts and allows torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

 to be transmitted through. For a key to function the shaft and rotating machine element must have a keyway, also known as a keyseat, which is a slot or pocket for the key to fit in. The whole system is called a keyed joint. A keyed joint still allows relative axial movement between the parts.

Commonly keyed components include gear
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....

s, pulley
Pulley
A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference. A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present...

s, and coupling
Coupling
A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.The...

s.

Parallel keys

Parallel keys are the most widely used. They have a square or rectangular cross-section. Square keys are used for smaller shafts and rectangular faced keys are used for shaft diameters over 6.5 in (16.5 cm). Set screws often accompany parallel keys to lock the mating parts into place so they do not move. The keyway is a longitudinal slot in both the shaft and mating part.

Woodruff keys

Woodruff keys are semicircular
Semicircle
In mathematics , a semicircle is a two-dimensional geometric shape that forms half of a circle. Being half of a circle's 360°, the arc of a semicircle always measures 180° or a half turn...

 shaped keys that, when installed, leave a protruding tab. The keyway in the shaft is a semi-circular pocket and the mating part has a longitudinal slot. They are used to improve the concentricity of the shaft and the mating part, which is critical for high speed operations. The main advantage of the Woodruff key is that avoids the milling of a keyway near shaft shoulders, which already have stress concentration
Stress concentration
A stress concentration is a location in an object where stress is concentrated. An object is strongest when force is evenly distributed over its area, so a reduction in area, e.g. caused by a crack, results in a localized increase in stress...

s.

Common applications include machine tool
Machine tool
A machine tool is a machine, typically powered other than by human muscle , used to make manufactured parts in various ways that include cutting or certain other kinds of deformation...

s, automotive applications, snowblowers and marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...

s.

This type of key was developed by W.N. Woodruff of Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...

, who was presented in 1888 with the John Scott Medal by the Franklin Institute
Franklin Institute
The Franklin Institute is a museum in Philadelphia, Pennsylvania, and one of the oldest centers of science education and development in the United States, dating to 1824. The Institute also houses the Benjamin Franklin National Memorial.-History:On February 5, 1824, Samuel Vaughn Merrick and...

 for the invention.

Tapered keys

The final type of key is the tapered key, which is tapered on one side, the side that engages the hub. The keyway in the hub is broached with a taper matching that of the tapered key. Some taper keys have a gib, or tab, for easier removal during disassembly. The purpose of the taper is to secure the key itself as well as to firmly engage the shaft to the hub without the use of a set screw. The problem with taper keys is that they can change the center of rotation of the shaft to be slightly off of the mating part.

Others

A "Scotch key" also provides a keyway not by milling but by drilling axially into the part and the shaft, so that a round key can be used.

Keyseating

Keyseating is the creation of the slots in the mating items. Keyseating can be done on a variety of different machines including a keyseater, a vertical slotting machine, a broacher, either a vertical or horizontal mill, or with a chisel and file.

Broaching

Broaching primarily used to cut square cornered internal keyways. The specific broach, bushing and guide are used for each given keyway cross-section, which makes this process more expensive than most of the alternatives. However, it can produce the most accurate keyway out of all the processes. There are three main steps in broaching a keyway: First, the workpiece is set on the arbor press
Arbor press
An arbor press is a small hand operated press. It is typically used to perform smaller jobs, such as staking, riveting, installing and removing bearings and other press fit work. Punches, inserters, or other tools/dies may be added to the end of the ram depending on the desired task. Arbor presses...

 and the bushing is placed in the opening of the workpiece. Next, the broach is inserted and pushed through, cutting the keyway. Finally, shim
Shim
A shim is a thin and often tapered or wedged piece of material, used to fill small gaps or spaces between objects. Shims are typically used in order to support, adjust for better fit, or provide a level surface...

s are placed between the bushing and the broach to achieve the correct depth necessary for the key.

Keyseater

Keyseaters, also known as keyseating machines and keyway cutters, are specialized machines designed to cut keyways. They are very similar to vertical shapers
Shaper
A shaper is a type of machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to machine a linear toolpath. Its cut is analogous to that of a lathe, except that it is linear instead of helical...

; the difference is that the cutting tool
Cutting tool
In the context of machining, a cutting tool is any tool that is used to remove material from the workpiece by means of shear deformation. Cutting may be accomplished by single-point or multipoint tools. Single-point tools are used in turning, shaping, plaining and similar operations, and remove...

 on a keyseater enters the workpiece from the bottom and cuts on the down-stroke, while the tool on a shaper enters the workpiece from the top and cuts downward. Another difference is a keyseater has a guiding system above the workpiece to minimize deflection, which results in a closer tolerance cut. The process starts by clamping the workpiece to the table with a fixture or vise
Vise
Vise may refer to:* Miami Vise, a defunct AFL team* Vise , a mechanical screw apparatus* Vise , an architectural element* Venus In-Situ Explorer * The Vise, TV show* Visé, BelgiumPeople with the surname Vise:...

. The workpiece is properly located and then the reciprocating arm is started. Some models have a stationary table so the cutter is fed horizontally into the workpiece, while others have a movable table that feeds the workpiece into a fixed cutter. These machines can cut other straight sided features other than keyways (see the picture). They can also produce blind slots, which are slots that do not extend through the whole workpiece.

Milling

Parallel, tapered, and Woodruff keyways can be produced on a milling machine
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

. End mills or slotting cutters are used for parallel and tapered keyways, while a Woodruff cutter is used for Woodruff keyways.

For internal keyways that are not too long, the keyways can be milled if a radius is acceptable.

Chiseling

One of the earliest forms of keyseating was done by chisel
Chisel
A chisel is a tool with a characteristically shaped cutting edge of blade on its end, for carving or cutting a hard material such as wood, stone, or metal. The handle and blade of some types of chisel are made of metal or wood with a sharp edge in it.In use, the chisel is forced into the material...

ing. The keyway is roughed out using a chisel and then filed
File (tool)
A file is a metalworking and woodworking tool used to cut fine amounts of material from a workpiece. It most commonly refers to the hand tool style, which takes the form of a steel bar with a case hardened surface and a series of sharp, parallel teeth. Most files have a narrow, pointed tang at one...

to size; the key is tried frequently to avoid over filing. This technique is long, tedious, and rarely used anymore.

Keyed joints

Two parallel keys can be used either 90° or 180° apart from each other if the shaft connection needs to be more robust.

Improperly machined keyways that had cutter deflection or drifting occur, may not be strong enough for the required application.

External links

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