Profile Turning: German and English Methods of Machining Cams and Similar Profiles

THE machining of profiles on such pieces as the cams of internal‐combustion engine camshafts presents a problem which can be solved in two ways. The original method was to attempt to machine these portions of the shaft in the normal way, providing a special rocking tool‐holder in order to ensure that the cutting angle of the tool remained constant. The diagram fig. 1 shows one example of German practice in this respect, from which it will be seen that the tool‐holder for each cam is of the rocking type, whose angle of tilt is under the control of a large master cam, timed to give one revolution for each revolution of the workpiece, and which during that revolution constantly varies the degree of tilt and consequently the angle of presentation of the tool to the piece. Apart from this, the profile of the cam also necessitates a series of advances and withdrawals of the tool for each revolution of the piece; this is controlled by a somewhat similar master cam at the rear of the tool‐holder. From the foregoing, it will be seen that although the difficulties of machining are overcome, it is only by somewhat cumbersome and extremely expensive methods on a very special machine.