What Is a Woodruff Key? | Why Use a Woodruff Key? | Sunk Keys

What Is a Woodruff Key?

Woodruff key is a semi-circular disc & fits into circulars recess in the shaft, which is machined by Woodruffs keyway cutter. The shaft may be parallel or tapered, showing the method of dimensioning shafts for the Woodruff key where the depths of the recess from the outsides of the shaft are given, in addition to the diameter of the recess.

Woodruff keys have the advantage that they will turn themselves into their circular recess to accommodate any tapers in the mating hub on the assembly; For this reason, it cannot be used as a pawn key, as it would jam.

Woodruffs keys are commonly used in machine tools and, for example, between the flywheel and crankshaft of a small internal combustion engine, where the drive depends largely on the fit between the shaft and the conical rugged flywheel hub.

The keyway in the shafts is a semi-circular pocket, the mating parts, a longitudinal slot. They are used to improves the concentricity of the shafts & mating part, which is important for high-speed operation. The circular section can be cut directly by plunge cutting with a circular woodruff cutter without any relief.

The main advantage of Woodruff keys is the elimination of milling near the shaft shoulders, where stress concentrations and concentrations would be affected. A more precise fit of the key and keyway also reduces play and stress concentrations and improves the reliability of the key.

The Woodruff keys is a semi-circular disc and fit into a circular recess in the shafts, which is machined by a Woodruffs keyway cutter. These Woodruff keys are mostly used in machines, tools & automobile shafts ” to 2½” (6 mm to 60 mm) in diameter. Woodruff keys are not capable of bearing the same weight as long parallel keys.

The advantage of the Woodruff key is that it is able to accommodate any taper in the hub keyway, its captive and depth preventing the key from turning over. Disadvantageous or drawbacks of woodruff keys are that the depth of the keyway weakens the shaft, cannot be used as a feather key, is difficult and small to install. Installing two or more Woodruff keys to lift the bulk of the load is expensive and makes installation more problematic.

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Why Use a Woodruff Key?

Mains advantages of a Woodruff key are the elimination of milling near the shaft shoulders, where stress concentrations and concentrations would be affected. The latter is especially important for high-speed operations. It has the advantage that it will fold itself into its circular recess to accommodate any tapers in the mating hub on the assembly; For this reason, it cannot be used as a pawn key because it will jam.

Woodruff is commonly used in machine tools and, for example, betweens the flywheels and crankshaft of a small internal combustion engine, where the drive depends largely on the fit between the shaft and the cone-bored flywheel hub.

An added advantage is that while a stuck key can be removed from the shaft with a hammer, the circular profile will push the key out of the slot, unlike a standard key that would need to be pushed axially or out of its slot. I will have to take it out. Common applications include machines tools, automotive applications, snowblowers.

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Sunk Keys:

Recessed keys are immersed in the shaft for half the thickness, where measurement is taken on the side of the key. Not along the centerline through the shaft.

#1. Rectangular

As shown, rectangular keys are wider than their height and are sometimes called flat keys. This is used on shafts up to about 500 mm or 20″ in diameter. The additional key width allows it to transmit greater torques without increasing the depth. An increase in depth means weaker shafts due to a decrease in the effective shaft cross-sectional area.

#2. Square Keys

Square keys, as their name suggests, are keys of square cross-section and are usually specified for shafts up to about 25 mm or 1″. They can be used for larger shafts when a deeper key depth than rectangular keys is desirable. An increase in depths means a weaker shaft due to a decrease in the effective shaft cross-sectional area.

#3. Parallel Sinking Keys

Parallel sinking keys can be either rectangular or square sections but without taper. These keys are cheap and readily available’s. It is one of the easiest to installs. But the keys need to be held through the hub, ideally by a set screw.

Because vibration or reversal of rotational direction often throws the key out. These keys are usually fitted tightly to the bottom of the shaft keyway and to the sides of the key joint, leaving clearances at the top of the hub keyway.

#4. Gib Head Sunk Keys

A gib head-on, the sunk key is added to make it easy to remove. As shown in, gib head eccentric keys are typically rectangular or square keys that have a taper on the top surfaces to ensure a tight fit.

#5. Feather Keys

Feather keys are attached to either the shaft or the hub to allow relative axial motion. As shown in the figures, they are three main wing keys. Double-headed, peg feather, and feather key. This enables power transmission between shaft and hub with parallel opposite faces, as well as allowing it to slide.

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Advantages of Woodruff Key:

Here, the different advantages of woodruff key are as follows

• This is an easily adjustable key.
• This hub is capable of accommodating any taper in the keyway,
• This is a more precise fit of the key and also reduces keyway play and stress concentrations, and improves the reliability of the key.
• This ends milling near the shaft shoulders, where stress concentrations and concentrations will be affected.
• This is especially important for high-speed operations.
• This harness is useful at the ends of the shafts. Its extra depth in the shafts prevents any tendency for it to overturn in its keyway.

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Frequently Asked Questions (FAQ)

Woodruff Key

A woodruff key, also known as a half‑moon key, is a semi-circular machine shaft key that prevents gears, hubs, or other components from moving independently of a rotating shaft or spindle.

What Is a Woodruff Key?

Definition of Woodruff key:- a shaft key made in the form of a segment of a disk and used with shafts not more than 2¹/₂ inches in diameter.

Woodruff Keyway

The Woodruff key is a semi-circular disc and fits into a circular recess in the shaft which is machined by a woodruff keyway cutter. These woodruff keys are mostly used in machine tools and automobile shafts from ¼” to 2½” (6 mm to 60 mm) in diameter.

Square Keys

The cross-section of the key is either square or rectangular and hence the name. This is the most standardized version of keys currently being used in all applications. The size of the key is to be selected on the base of shaft size which is already been standardized for rectangular keys.

Shaft Key Types

• Saddle keys.
• Sunk keys.
• Parallel keys.
• Tapered keys.
• Square keys.
• Flat keys.
• Gib head keys.
• Feather keys.

Key Woodruff

This type of key was developed by William N. Woodruff of Hartford Connecticut. In 1888, he was awarded the John Scott Medal by the Franklin Institute for his invention.

Wood Ruff Key

Woodruff keys are semi-circular discs used to connect machine parts to rotating shafts and spindles. They serve to stop gears or other machine parts from moving independently from the rotating shaft and are often installed into the recessed key seats cut into the said shafts

Taper Sunk Key

This type of sunk key, the head is used to reduce the impact of the hammer thus preventing damage to the shaft. The gib head key tapers in 1: 100 in thickness. These keys are mostly used to hold the gears and pulleys tightly on the shaft.

Woodruff Key Is Used for

Woodruff keys are semi-circular discs used to connect machine parts to rotating shafts and spindles. They serve to stop gears or other machine parts from moving independently from the rotating shaft and are often installed into the recessed key seats cut into the said shafts.

Crankshaft Key

A crankshaft keyway is actually a keyseat groove or a pocket machined into the shaft. On the other hand, keyways are slots machined into a hub and provide space for the key to be inserted. The entire system is referred to as a keyed joint.

What Is a Woodruff Key Used for?

Woodruff keys are semi-circular discs used to connect machine parts to rotating shafts and spindles. They serve to stop gears or other machine parts from moving independently from the rotating shaft and are often installed into the recessed key seats cut into the said shafts.

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