Page:Practical Treatise on Milling and Milling Machines.djvu/183

Rh CHAPTER IX Milling Operations — Cam Cutting, Graduating and Miscellaneous Operations

Cam Cutting. Face, peripheral and cylindrical cams of all ordinary sizes can be cut upon a milling machine, and a far more satisfactory job can be obtained than is possible by drilling around the outline on a cam blank, breaking it off and then milling or riling to a line.

When it is required to cut several cams of the same outline at frequent intervals, it is an advantage to add the cam cutting attachment, illustrated and described in Chapter V, to the equipment of the machine. The formers that are required to produce the different cams can be preserved, and it is then only a matter of a few minutes' time to set up the machine to cut any number of cams for which a former is at hand.

Another method that is often followed, in cutting peripheral cams, especially those for use on automatic screw machines, is that of using the spiral head and a vertical spindle milling attachment. Illustrations of this are shown on pages 187 and 188. The spiral head is geared to the table feed screw, the same as in cutting ordinary spirals, and the cam blank is fastened to the end of the index spindle. An end mill is used in the vertical spindle milling attachment, which is set in each case to mill the periphery of the cam at right angles to its sides, or, in other words, the axes of the spiral head spindle and attachment spindle must always be parallel to mill cams according to this method. The cutting is done by the teeth on the periphery of the end mill. The principle of this method is as follows: Suppose the spiral head is elevated to 90°, or at exact right angles to the surface of the table (see Fig. 69), and is geared for any given lead. It is then apparent that, as the table advances and the blank is turned, the distance between the axes of the index spindle and attachment spindle becomes less. In other words, the cut becomes deeper and the radius of the cam is shortened, producing a spiral lobe, the lead of which is the same as that for which the machine is geared.