Complete Guide to Woodruff Keys & Keyways: Design & Functions

What is Woodruff Key?

Woodruff key is a flat semi-circular or half-moon-shaped disk with a uniform thickness, which directly fits into the semi-circular recess of the shaft. The semi-circular recess or pocket is known as the woodruff keyway. Semi-circular pocket in the shaft directly cut by woodruff key cutter. The bottom circular portion is placed in the shaft by hammering & the top flat portion is inserted into the keyway of the hub.

Although, this key is easy to remove & hard to install. Small tolerance between key and keyway which helps to reduce stress concentration and increases reliability. Due to extra depth in the shaft, there are chances of weakening of shaft strength ability.

Due to the extra depth of the key, it directly fits in the mating part, and there is no gap between those parts. These keys are easy to use and adjustable as compare to other keys.

This type of key is mainly using for light loads. It is suitable for shafts whose diameter ranges between 6mm to 60 mm.

This key is not suitable for heavy load and torque. Mounting more than two keys to transmit high torque increases cost and reduces shaft strength.

Different Types of Woodruff Key

There are mainly two types of Woodruff keys as per application. But the difference between them is minimum.

Full Radius

It is full half-circular in shape. It makes contact with the seat of the shaft when fixing it. This key requires high precision tight fit tolerance. Because small deviation in size cannot make an assembly with the hub.

Flat Bottom

It is in the same shape as the standard key, with the bottom is flat. Due to that, it can adjust in the groove easily. As the bottom is flat, it becomes compact with less weight.

High Pro Key

It has a full half-circular shape at the bottom & a slightly different profile at the top. The step is at the flat portion on top to get support during assembly. The above figure gives more detailed information about high pro woodruff kay.

Read more- What is the shaft? Types, Material, and Design

Why use a woodruff key?

As it fixes in the circular recess of the shaft, it can adjust as per the taper in the mating hub. Reduces stress concentration in shaft shoulder area due to elimination of milling near to it. As it has a half semi-circular shape, it can be removed very easily by applying moderated pressure with a hammer on the edge. So circular slot directly pushes the key out of the slot. But standard keys require axial force to remove them.

How to install the woodruff key properly?

• While installing the woodruff key, first align the key with the pocket (Keyway) of the shaft & press that key in a shaft manually.
• If it is not getting fix with the keyway, then hammer manually with light force on key to get fix.
• Once it gets fit in the shaft, align the flat surface of the key with the slot of the hub. 
• As per the condition, we can move the hub or shaft with the key in each other to get proper assembly.
• By light tapping with a hammer, we can make an assembly of shaft & coupling.

Woodruff key materials & finish.

Material of the woodruff key is stainless steel, alloys, and carbon steel. Because carbon steel & alloy steel are durable in nature. These keys can be prevented by corrosion by using different kinds of coatings.

Advantages of Woodruff key.

• The Woodruff key is simple and easily adjustable.
• Due to the exact fit of the key, there is no gap between the shaft & key. It reduces stress concentration & improves the reliability of the shaft.
• Mostly used in the tapered shaft where all others key fails.
• It is typically useful in high-speed applications.
• It can tilt and align according to the movement of the shaft.
• Easy to remove.

Disadvantages of Woodruff Key

• Woodruff key is difficult to install because of its groove.
• Due to high depths, there are chances of reduction of strength in the shaft.
• It is not suitable to carry a high load.
• No axial movement between shaft and mating part.