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.
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, and snowblowers.
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.
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.
Frequently Asked Questions (FAQs)
What Is a Woodruff Key?
A Woodruff key is a semi-circular disc that fits into a circular recess in the shaft, which is machined using a Woodruff keyway cutter. It is commonly used to improve the concentricity between the shaft and the mating part.
What Are the Advantages of Using a Woodruff Key?
The main advantages of using a Woodruff key include its ability to accommodate tapers in the mating hub, reduce play and stress concentrations, improve the reliability of the key, and eliminate the need for milling near shaft shoulders, which is particularly important for high-speed operations.
Where Are Woodruff Keys Commonly Used?
Woodruff keys are commonly used in machine tools, automotive applications, and small internal combustion engines, such as between the flywheel and crankshaft. They are also found in snowblowers and other machinery.
What Are the Different Types of Sunk Keys?
The different types of sunk keys include rectangular keys, square keys, parallel sinking keys, gib head sunk keys, and feather keys. Each type has its specific applications and advantages.
How Does a Woodruff Key Improve Shaft and Hub Concentricity?
The Woodruff key fits into a semi-circular pocket in the shaft and a longitudinal slot in the mating part, which improves the concentricity between the shaft and the mating part, reducing vibration and ensuring smoother operation.
Can a Woodruff Key Be Used as a Feather Key?
No, a Woodruff key cannot be used as a feather key. It is designed to accommodate tapers in the hub keyway and is not suitable for applications where a feather key is required.
What Are the Disadvantages of Using a Woodruff Key?
The disadvantages of using a Woodruff key include the weakening of the shaft due to the depth of the keyway, difficulty in installation, especially for small sizes, and the expense and complexity of using multiple Woodruff keys for heavy loads.
How Is a Woodruff Key Installed?
A Woodruff key is installed by first machining a semi-circular recess in the shaft using a Woodruff keyway cutter. The key is then inserted into the recess, and the mating part with a longitudinal slot is aligned and fitted over the key.
What Are the Common Sizes for Woodruff Keys?
Woodruff keys are typically used on shafts ranging from 6 mm to 60 mm (¼” to 2½”) in diameter. The specific size of the key depends on the application and the dimensions of the shaft and mating part.
Why Is a Precise Fit Important for Woodruff Keys?
A precise fit of the Woodruff key and keyway reduces play and stress concentrations, which improves the reliability and performance of the key, particularly in high-speed operations. It ensures a secure connection between the shaft and the mating part.
How Does the Circular Section of a Woodruff Keyway Benefit Its Installation?
The circular section of a Woodruff keyway can be cut directly by plunge cutting with a circular Woodruff cutter without any relief, making the installation process simpler and more efficient.
Are There Any Specific Applications Where Woodruff Keys Are Preferred?
Yes, Woodruff keys are preferred in applications where the elimination of milling near shaft shoulders is crucial, such as in high-speed machinery and precision equipment. They are also favored in automotive and machine tool applications for their ability to accommodate tapers and reduce stress concentrations.
