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		Feather Key Joints - Course: Techniques of fitting and assembling component parts to produce simple units. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 19 p.)
			(introduction...)
			Introduction
			Hints on Labour Safety
			1. Purpose of Feather Key Joints
			2. Kinds of Feather Keys and Profile Shafts
			3. Kinds of Feather Key Joints
			4. Stress on the Feather Key Joints
			5. Tools, Devices and Auxiliary Means
			6. Technological Processes for Manufacturing Feather Key Joints and Profile Shaft Joints
			7. Detachment of Feather Key Joints

2. Kinds of Feather Keys and Profile Shafts

Mostly, feather keys are made from drawn flat steel and have a tensile strength between 600 and 800 MPa. They may also be made by hand from sectional steel, if they are not available in the required dimensions.

Flat keys

These are elongated, rectangular bodies, straight or round-ended. For special functions within the joint they may be provided with bore holes to receive fillister-head screws. In addition, there may be a tapped hole in the centre of the key that enables that the key can be pressed out of the keyway with the help of a screw.

Figure 2 Flat keys

1 straight-ended, 2 round-ended, 3 with bore hole for locking screw, 4 with bore holes for locking screws and tapped hole for forcing screw

Woodruff keys

These are bodies that have the shape of a segment of a circle. They can transmit only low rotary powers, because the shaft keyway, which must be very deep, limits the strength of the shaft. They mainly secure the position of drive parts.

Figure 3 Woodruff key

Circular arc profile shafts

These shafts are also called K-shaped shafts or polygon shafts. They have a cross section in the form of a rounded equilateral triangle with long circular arcs as sides, and they are manufactured on profile turning machines or grinding machines.

They are able to transmit high rotary powers, because they create no notch effect. They are suitable for fitting connections of shaft and hub as well as for sliding connections, if the hub must be arranged in a movable way on the shaft.

Figure 4 Circular arc profile shaft

Spline shafts

These are shafts in the periphery of which an even number of splineways are cut at regular intervals. The splineways are rectangular and may be of different depth corresponding to the stress they have to stand. These shafts are preferably used for highly stressed couplings and speed-changing mechanisms of changing rotational direction. The internal profile of the hub is made on shaping or broaching machines.

Figure 5 Spline shaft

Serrated shafts

These are shafts in the periphery of which trapeziform internal teeth (serration) are cut at regular intervals; the internal teeth have straight or rounded flanks. The shafts are used with high and discontinuous rotary powers, but they are not suitable, if parts on them shall be shifted under load. Often, the hub is slotted and clamped on the shaft by a screw.

Figure 6 Serrated shaft

Hints for manufacturing feather keys

- Feather keys are made by hand only, if industrially prefabricated keys are not available. They can be worked with files and scrapers.
- Because the flanks of the feather keys are stressed, they must be carefully flattened by the file. To enable an accurate fitting in, they should be profiled with a slight allowance of 0.2 mm.

Sequence of operations

- Measuring of the shaft keyways and initial material;
- Testing of the clearance fit between shaft and hub;
- Filing the feather key true to size, slightly chamfering the edges;
- Drilling the holes for the holding screw as well as the tapped hole for the forcing screw;
- Putting in and fining of the feather key in the shaft keyway.

What are feather key joints?
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What are the special advantages of feather key joints?
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What is the disadvantage or feather key joints?
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What kinds of feather keys are distinguished?
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