GB575003A - An improvement in or relating to gear tooth forms and the production of the same - Google Patents

Abstract

575,003. Toothed gearing; gear cutting. MERRITT, H. E. Sept. 24, 1943, No. 15666. Convention date, Sept. 28, 1942. [Class 80 (i)] [Also in Group XXII] Gear teeth, particularly for clockwork and instruments, are derived from a basic rack, the faces and flanks of the tooth profiles of which consist of similar curves a, b composed of arcs of circles, the radii a<3>, b<1> of which are approximately equal to the pitch and which are arranged in alternate reversion, the centres of curvature a<2>, b<2> of the reversed arcs forming one side of a tooth being so positioned that the arcs osculate at the point of their intersection with the pitch line c and the pressure angle d is approximately 10 degrees. The radius of the arc a may differ slightly from that of the arc b to provide a small amount of tip relief. Gears with the proportions described and with an addendum approximately 0.8 times the module will be interchangeable. To give the larger clearance usually employed, the teeth of the cutter are thicker than one-half of the pitch. The teeth may be cut by a hob formed by a tool, either flank of which consists of two circular arcs having opposite and usually (but not necessarily) equal radii of curvature. The flanks of the forming tool are finished by a grinding wheel, the profile of which is trimmed by mechanical means to a convex arc which will produce the concave portion of the profile of the tool corresponding to the arc b. The convex portion of the tool corresponding to the arc a, the grinding wheel and supports are rotatably mounted about an axis through the centre of curvature of the convex portion of the tool. The wheel support is given a gradual angular motion about its axis of rotation. For a tool of rectilinear form, the cutter will be reciprocated relatively to the wheel. The wheel may be replaced by a cutting tool. Specification 274,667, [Class 80 (i)], is referred to.