Machinery's Handbook, 31st Edition
COUPLINGS and Clutches 2531 load. The teeth of positive clutches are made in a variety of forms, a few of the more com- mon styles being shown in Fig. 1. Clutch A is a straight-toothed type, and B has angular or saw-shaped teeth. The driving member of the former can be rotated in either direction; the latter is adapted to the transmission of motion in one direction only, but is more read- ily engaged. The angle θ of the cutter for a saw-tooth clutch B is ordinarily 60 degrees. Clutch C is similar to A , except that the sides of the teeth are inclined to facilitate engage- ment and disengagement. Teeth of this shape are sometimes used when a clutch is required to run in either direction without backlash. Angle θ is varied to suit requirements and should not exceed 16 or 18 degrees. The straight-tooth clutch A is also modified to make the teeth engage more readily, by rounding the corners of the teeth at the top and bottom. Clutch D (commonly called a “spiral-jaw” clutch) differs from B in that the surfaces e are helicoidal. The driving member of this clutch can transmit motion in only one direction.
B D Fig. 2. Diagrammatic View Showing Method of Cutting Clutch Teeth Cutter Clutch Blank C
A
a
d
Fig. 3. Clutches of this type are known as right- and left-hand, the former driving when turning to the right, as indicated by the arrow in the illustration. Clutch E is the form used on the back-shaft of the Brown & Sharpe automatic screw machines. The faces of the teeth are radial and incline at an angle of 8 degrees with the axis, so that the clutch can readily be disengaged. This type of clutch is easily operated, with little jar or noise. The 2-inch (50.8 mm) diameter size has 10 teeth. Height of working face, 1 ⁄ 8 inch (3.175 mm). Cutting Clutch Teeth.— A common method of cutting a straight-tooth clutch is indicated by the diagrams A , B and C , Fig. 2 , which show the first, second and third cuts required for forming the three teeth. The work is held in the chuck of a dividing-head, the latter being set at right angles to the table. A plain milling cutter may be used (unless the corners of the teeth are rounded), the side of the cutter being set to exactly coincide with the centerline. When the number of teeth in the clutch is odd, the cut can be taken clear across the blank as shown, thus finishing the sides of two teeth with one passage of the cutter. When the number of teeth is even, as at D , it is necessary to mill all the teeth on one side and then set the cutter for finishing the opposite side. Therefore, clutches of this type commonly have an odd number of teeth. The maximum width of the cutter depends upon the width of the space at the narrow ends of the teeth. If the cutter must be quite narrow in order to pass the narrow ends, some stock may be left in the tooth spaces, which must be removed by a sep arate cut. If the tooth is of the modified form shown at C , Fig. 1, the cutter should be set as
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