Woodruff Key : Types | Why Used | Advantages and Disadvantages

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What is Woodruff Key?

A Halfmoon key or woodruff key is a semi-circular machine shaft key that stops gears, hubs, or other components from moving independently of a spinning shaft or spindle. A woodruff key cutter or arbour cutter creates a key seat for the woodruff keys. The shaft is then pushed with gear or other components with a woodruff keyway until the woodruff key interacts with its keyway.

woodruff key diagram

The top flat half is fitted into the hub keyway, while the bottom circular part is hammered into the shaft. This key, on the other hand, is both easy to remove and complex to install.

A narrow tolerance key and keyway can help to reduce stress and promote safety by reducing stress concentration.

Why Use a Woodruff Key?

It can adjust to taper into the mating hub because it is readily fastened in the circular hole or dip of the shaft. As a result of the absence of milling near the shaft shoulder, the stress concentration in that area is reduced.

It can be easily removed when it is half semi-circular in shape by using moderate pressure with a hammer on the edge. As a result, the key is pushed straight out of the circular slot. Standard keys, on the other hand, require axial force to bend.

The fundamental benefit of the Woodruff key is that it eliminates machining near shaft shoulders, which would influence stress concentrations and concentricity. For high-speed operation, the latter is especially critical.

Related Article: Shaft Key- Types, Advantages and Disadvantages

Working of Woodruff Key-

The woodruff shaft key’s long, flat face spreads over the host shaft when it’s inserted. The projecting part of the key locks components together when a matching hub, gear, or other component is forced into the shaft.

Installation of Woodruff key-

The half-moon notch cut into the shaft is the woodruff keyseat. The curved part of the woodruff key is pressed into the keyseat. The keyway, on the other hand, is the slot carved into the mating part to accept the flat side of the woodruff key.

Related Article:The Splines Key

Types of Woodruff Key-

The following are the different varieties of woodruff keys to be aware of:

Full Radius Key-

Woodruff keys with a complete radius are a full half-circle in diameter and make full contact with the shaft keyway. Because contact between the woodruff key and the bottom of the seat can cause interference and the key to extend from the groove higher than desired, full radius woodruff keys necessitate precision of the seat groove.

The full radius key looks like a full half-circular moon and may contact the groove seat completely. When it’s fixed, it touches the shaft seat. This type of woodruff key is known for its high precision and close fit tolerances. This is due to the fact that even minor variations in size do not mix with the hub.

Full radius woodruff keys diagram

Flat Radius Key-

Woodruff keys with a flat bottom have the same profile as conventional woodruff keys, but the bottom has been shaved flat.

The flat bottom avoids interference at the seat’s bottom, allowing the woodruff key to fully seat in the groove and avoiding potential clearance concerns caused by high key height.

Flat radius key diagram

Hi-Pro Key-

HiPro keys are a type of woodruff key with a full radius and foot. The feet extend over the face of the host shaft once mounted, preventing the key from swinging back and forth in its rounded seat, also often referred to as high-profile woodruff keys.

Hi pro key

Related Article- Involute Splines- Definition, Types, Materials Selection and Applications

Materials Used in Woodruff Keys-

Carbon steel, alloy steel, and stainless steel are used to create Woodruff keys. Both carbon steel and alloy steel woodruff keys are durable, however, to avoid corrosion, they must be plated or coated.

In terms of corrosion resistance, stainless steel woodruff keys outperform carbon and alloy steel, although they aren’t as strong.

Advantages of Woodruff Keys-

The following are some of the benefits of woodruff keys to consider:

  • Easy Adjustable
  • Suitable for High-speed rotating components
  • useful in the reduction of stress concentration
  • improves safety
  • precise fit
  • Less likely to roll over with a deep seat in the shaft

Disadvantages of Woodruff Keys-

Woodruff keys have the following drawbacks to be aware of:

  • Shaft strength is decreased by deeper groove depths.
  • It is tough to install since it can rock during assembly.
  • Compared to longer machine keys, it carries less weight.
  • A woodruff key cutter is used to machine the key seat.


Wrapping Up-

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