Robey-Smith bevel gear cutting machine, patented 1895

This is the original experimental machine invented by Mr J. Buck in 1895. It illustrates an early stage in the development of the planing or shaping type of gear cutter subsequent to the application of the simple shaping machine to such work and was the first machine in which both sides of the tooth were cut simultaneously. The tooth curve is an arc of a circle, generated upon the principle of the odontograph and is a circular approximation to the involute.

The blank to be cut is placed upon the spindle which carries an index plate corresponding to the number of teeth required, the whole being mounted on a saddle which is pivoted about an axis representing the apex of the cone. The blank is fed to the cutters by swinging this saddle about the pivot.

The two cutting tools and tool holders are reciprocated simultaneously by crank motions and the tool slides are pivoted about an axis enabling the cutting edges of the tools to move on lines which converge at the apex of the pitch cone as viewed in slide elevation. After each stroke of the cutting tools the gear blank is indexed round one tooth-space, so that after cuts have been taken along the sides of one tooth the next stroke will make cuts along the side of the next adjacent tooth and so on round the blank. After a complete revolution of the blank the saddle is fed towards the tools for a further series of cuts. In order to generate the toothform a parallel motion by a disc with suitably developed slots engaging pins on the extremities of the tool slides is provided to separate the cutter slides gradually in proportion to the depth of cut taken into the blank.

The curvature of the flanks of the teeth depends upon the ratio existing between the rate of separation of the tool slides and the feed of the tools into the blank.