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When working out the preliminary draft of the machine setup it is diffi- . cult to decide from which table to take the data on idle movements , the production rate for the given part being as yet unknown . In p ractice , there rocker and headstock cams from Table 1 5 . TABLE 15 Camshaft rotation angle for idle movements Function of the cam Section of the cam profile Headstock displacement Rise for headstock advance Rocker control Rise for advancing tool No. 2 Drop for advancing tool No, 1 Shift of tool slides Nos. 3, 4, 5 Rise for advancing the tools · Drop for withdrawing the tools Drilling attachment control Drill retraction for multiple drilling Drilling and threading attach- Rise and drop of the lever ment spindle selection control Closing the collet Collet releasing and closing Releasing the collet control Number of cam degrees per 1 mm rise or drop of the cam profile (idle movement) 1' per mm, but not less than 3' 0.5' per mm, but not Jess than 3' 1' per mm, but not Jess than 3' 0.5' per mm, but not Jess than 3' 1' per mm, but not less than 3' 0.5' per mm, but not less than 3' 0, 75' per mm, but not less than 3' for the entire operation 20' 15' 1 0' After the preliminary calculation and the determination of the approximate production rate of the machine for the part in question, the definitive s etup is calculated using the idle movements taken from the tables; and on the basis should be used i n the final calculation only for the tool-slide cams [ 3 , 4 , 5 ], the collet cams and the attachment cam s . Safety dwells o f 2 t o 3° each are added when necessary to the values o f the movements obtained in the s etup calculation, in order to compensate for pos sible inaccuracies in the m anufacture of the cam p rofil e . Laying out flat cam s . The cam profiles must produce the uniform headstock o r tool feed rate adopted with the s election of the cutting conditions . This condition is s atisfied by the A rchimedean spiral . In order to plot the A rchimedean spiral the angle of rotation of the cam corresponding to the given operation is split into s e veral e qual parts on the arc of a circle and rays are traced, connecting the center with the points of division. The height of ris e is spli� into an equal number of parts and concentric circles are drawn accordingly. A continuous curve is drawn through the inters ections of the rays with the corresponding circles and the resulting curve is an A rchimedean spiral . Figure 2 7 s hows an A rchimedean spiral plotted on the s ector from 9 6 ° to 1 9 0°. The rise is 1 9 . 9 mm . In order that the interaction between cam and follower b e correct, the angle 6 between the tangent to the cam at the point of tangency and the per p endicular to the ray radius at the point of tangency, X1 Xp must not exceed some specified value (Figure 2 7 ). 1 29 |