First Method

The second process, that of planing the forms of the teeth, is accomplished by three methods. One is to form a planing tool to the exact contour of the space between the teeth, and by successive strokes of any machine having a reciprocating ram to carry the tool, some fixture for holding the gear blank, and a device for indexing the tooth spaces. This work is frequently done on a shaper and sometimes on a planer. This method produces a cut with parallel sides the same as a revolving cutter, and the depth of the cut may be varied at the two ends so as to be adaptable to bevel gear work although producing work that is no more theoretically correct than that of the revolving cutter. This device may be used upon spur gears, internal gears, racks, etc., with fairly good effect, but is a comparatively slow process. It may, however, be sometimes used where a milling machine or ordinary gear cutter cannot, as in cutting the teeth of internal gears.

Second Method

The second method, of planing gear teeth-which has proven an important device for forming the teeth of spur gears, internal gears, and racks-operates by means of a circular cutter upon which the teeth are formed similar to the teeth of the gear itself. This is the system used in the Fellows gear shaper. The action of the cutter is shown in Fig. 277. The gear blank is mounted on a proper spindle, and the machine started, the cutter reciprocating on its center line and parallel to its axis. The cutter is then fed toward the blank, and cuts its way to the proper depth. At this point, both the cutter and the blank begin to rotate in the directions indicated by the arrows, the cutter maintaining its reciprocating motion. This rotation of the cutter and the blank is obtained by separate and external mechanism, which insures that the movement shall be the same as though the cutter and the blank were two complete gears in correct mesh. The combined result of rotary and reciprocating motions is that the cutter teeth generate conjugate teeth in the blank, which mesh correctly with the cutter teeth and with one another. Any two gears of the same pitch cut with this cutter will mesh correctly together.

Fig. 277. Planing Gear Teeth.

Third Method

A third method of planing gear teeth, and one of very great importance, particularly in forming the teeth of bevel gears, is used by various gear-cutting machine builders. In some cases the tool slide travels upon a carriage whereof one end is pivoted directly under the apex of the base cone, and its opposite or outer end is properly guided to the exact contour of the tooth, which is formed by a tool having a single cutting edge with a narrow and somewhat rounded cutting point. In other cases the tool slide is in a fixed plane, while the arbor upon which the gear blank is mounted is journaled in a portion of the machine so constructed as to give the necessary adjustment and movements to the gear blank. These planing processes will be more particularly noticed later in describing the various types of gear-cutting machines.