Machinery's Handbook, 31st Edition
CAMS AND CAM DESIGN 2387 the cam roll during the given part of the cycle, and c is the movement corresponding to b , but on a circle the diameter of which is equal to that of the cam at the bottom of the groove. With the same throw a as before, the line OV will be the development of the cam at the bottom of the groove. OU then is the length of the helix traveled by the top of the roll, while OV is the travel at the bottom of the groove. If, then, the top width and bottom width of the groove be made proportional to OU and OV , the groove will be properly proportioned.
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Fig. 23. Shape of Rolls for Cylinder Cams Cam Milling.— Plate cams having a constant rise, such as are used on automatic screw machines, can be cut in a universal milling machine, with the spiral head set at an angle α , as shown by the illustration.
Cam
a
Cutter
Fig. 24. When the spiral head is set vertical, the “lead” of the cam (or its rise for one complete rev olution) is the same as the lead for which the machine is geared; but when the spiral head and cutter are inclined, any lead or rise of the cam can be obtained, provided it is less than the lead for which the machine is geared, that is, less than the forward feed of the table for one turn of the spiral-head spindle. The cam lead, then, can be varied within certain limits by simply changing the inclination α of the spiral head and cutter. The following formula is for determining this angle of inclination, for a given rise of cam and with the machine geared for a lead, L , selected from the tables beginning on page 3528 , sin L r 360 # # ° α φ = where α = angle to which index head and milling attachment are set from horizontal as shown in the accompanying diagram r = rise of cam in given part of circumference
L = spiral lead for which milling machine is geared φ = angle in which rise is required, expressed in degrees
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