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Woodruff Key: Types, Working, Cutter, Advantages, Uses [PDF]

In this article, you will learn what is Woodruff Key? Its working, Installation, advantages, disadvantages, applications, and types of woodruff keys are explained with diagrams.

Furthermore, you can also download the PDF file of this article at the end. 

What is Woodruff Key?

A Woodruff key is a key that prevents gears, hubs, or other components from moving independently of a rotating shaft or spindle. They also act as a protective component that protects costly parts by shearing under extreme loads.

Woodruff Keys
Woodruff Key

A Woodruff key is a half-moon like a semi-circle with a similar length that usually fits into the circular opening of the shaft. This circular opening is known as a circular pocket or recess or is more commonly referred to as a woodruff keyway.

As it is generally defined, Woodruff keyways are semi-circular pockets that are driven into shafts to hold Woodruff keys. These pockets in shafts are directly cut by using woodruff keyway cutters.

The bottom circular part is hammered into the shaft and the top flat part is inserted into the hub keyway. However, this key is easy to remove and difficult to install. A small tolerance key and keyway helps to reduce stress concentration and increase safety.

How Woodruff Keyway Works?

The long flat face of the Woodruff key extends over the host shaft when installed. During a mating hub, gear, or other component is pressed onto the shaft, the protruding part of the key locks the components together.

It is important for the key to be somewhat comfortable and stable on the main seat. If the key is not good/steady, the curved profile on the bottom can cause the key to slide out of the key seat.

The strength capability of the shaft is likely to be weakened due to the additional depth in the shaft. And due to the added depth of the key, it fits directly into the mating part, and there is no gap between those parts.

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Installation of Woodruff Key

Image: Triumph Experience

When installing a Woodruff key, initially you must align the key with the pocket (keyway) of the shaft and manually press that key into the shaft by applying force. If it doesn’t fix with the keyway, manually hammer the key with light force to fix it, making sure it doesn’t break.

Once it fits into the shaft, next you need to align the top, with the flat side of the key so that it is parallel to the host shaft. According to the condition, we can move the hub or shaft into each other with the key to get the proper assembly.

During installment, woodruff keys sometimes pop out of their grooves as the mating component is pressed. This can make installing Woodruff keys difficult. So by lightly hitting with a hammer, we can make the assembly of the shaft and the coupling.

Types of Woodruff Key

Most often, Woodruff keys manufacture with a full radius and a flat radius. Furthermore, both perform similar functions but may be suitable for different applications. It is important to know the different types of woodruff keys, they are as follows.

  1. Full radius key
  2. Flat radius key
  3. Hi-pro key

1. Full Radius Key

Full Radius Key

The full radius key is almost similar to a full half-circular like a moon and can make full contact with the groove seat. This means it comes into contact with the shaft seat when it is fixed.

Generally, this type of woodruff key has high precision as well as tight fit tolerances. This is because even a very small deviation from the size does not combine with the hub.

2. Flat Radius Key

Flat Radius Key

This type of Woodruff key has the same profile as standard Woodruff keys. However, the bottom of the key has been cut flat. Because of that, it can easily adjust to the groove.

In this way, the flat bottom minimizes the possibility of interference with the bottom of the seat, allowing the Woodruff key to sit more fully in the groove and minimizing potential clearance issues of excessive key height. Since the bottom is flat, it becomes compact with less weight.

3. High Pro Key

High Pro Key

High pro keys are a modification of Woodruff keys that have a full radius but have the added feature of two legs. The High Pro key has a full half-circular shape at the bottom and a slightly different profile at the top.

The steps are on a flat part at the top for support during the assembling of parts. When installing them, the legs extend over the face of the host shaft, preventing the key from moving in its round seat.

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Woodruff Cutters

If you need to attach a part to a shaft, you need a key cutter. A key cutter, also known as a woodruff cutter, is a very essential tool used to cut keyways for woodruff keys. The edges are slightly hollow for woodruff cutter relief and the teeth are not side cutting.

Image: IndiaMart

When cutting the keyway into the shaft, a key is inserted into the seat and the two parts can now be joined together. This technique is used for parts such as gears, hubs, or pulleys.

Typically, a woodruff key slot milling cutter is used for woodruff keys. These instruments are made from high-quality raw material which is considered to be of world-class quality and best performance. A high-speed steel 5% cobalt tool suitable for general cutting on all materials.

Why do Woodruff keys use?

Since it is easily fixed in the circular opening or recess of the shaft, it can adjust accordingly to taper into the mating hub. It, therefore, minimizes the stress concentration in the shaft shoulder area due to the elimination of milling near it.

When it is half semi-circular in shape, it can be easily removed by applying moderate pressure with a hammer on the edge. So the circular slot pushes the key straight out of the slot. But they require axial force to deflect standard keys.

Woodruff keys are also nearly as small and may not bear the same amount of weight as heavier keys. They are used for light-duty applications and to mount taper-bore components on tapered shaft ends.

Advantages of Woodruff Keys

  1. Using these keys, you can adjust them easily, and are quite simple too. Also, they are easy to remove.
  2. As the key is properly fitted, there is no gap between the shaft and the key. Hence reduces the stress concentration and improves the safety of the shaft.
  3. These types of keys are perfect for high speed operating systems.
  4. Since they’re adjustable, they can lean into the main seat or keyway and are able to adjust the taper in the hub keyway.
  5. They can provide a more precise fit while reducing movement in the key seat.
  6. The deep seat in the shaft minimizes the risk of the main seat rolling over.

Disadvantages of Woodruff Key

  1. These are not used where there is a high load carrying capacity.
  2. If the key has an extra depth of keyway into the shaft, this may increase the stress concentration and reduce its strength.
  3. The Woodruff key is quite difficult to install because of its groove design.
  4. The key does not allow axial motion between the shaft and the hub.
  5. They are not used for transmission of heavy torque such as multi-groove and V belt pulleys.

Wrapping It Up

A Woodruff key is a key roughly in the form of a semicircular disc fitting into a recess in a shaft. These keys are ideal for high-speed rotating assemblies, so they are used to lock gears and pulleys into shafts.

So for now, I hope that you have learned about the “Woodruff Key“. If you have any questions or doubts about this article, feel free to ask in the comments. If you got this article helpful, please share it with your friends.

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External Links:

  1. https://www.huyett.com/blog/woodruff-keys
About Yousef

He is a mechanical engineering student, he likes to write about engineering stuff and he is really interested in learning about new technology in machines.

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