Patent GB-466330-A (GB)
Title: Method and means for finishing gears
IPC: B23F19/06
Filed: 1936-10-19
Abstract: 466,330. Lapping gear wheels. FELLOWS GEAR SHAPER CO. Oct. 19, 1936, No. 28348. Convention date, Nov. 19, 1935. [Class 60] [Also in Group XXII] In a method of and machine for finishing an internal or external straight or helical toothed gear by running the gear in with a tool of conjugate gear form but different helix angle arranged with its axis inclined to the blank axis, the opposite side faces of the tool teeth are bowed longitudinally, Fig. 7, with respect to their median lines so that an extended contact is made for instance between the teeth of a tool c and an internal gear r, Fig. 4, whereas the contact for a straight toothed gear tool, Fig. 3, is limited to the end portions a, b if the angle of skew is larger than a few degrees. If the gears to be finished have considerable top and bottom clearance, the. tool gears may have the longitudinal convexity on their sides only. In other cases the root and outside circumferences are also convex. The tool gear may be of suitable material for burnishing or lapping or it may be provided with grooves so that it has both a burnishing and a cutting action. If the convexity is greater than that shown at c<2> then full contact occurs only at the middle of the tool gear and the contact diminishes towards the ends. In this preferred form a high unit pressure may be obtained between gear and tool without excessive total pressure. Such a tool is shown in Fig. 6. The teeth are bowed as shown exaggerated in Fig. 7, and are interrupted by grooves f to form cutting edges g. If the bearing is localized at the central region of the teeth the tool is reciprocated axially of the blank. In a machine embodiment the workpiece w, Fig. 1 is mounted on a carriage 2 which is reciprocated from a crank disc 8 through adjustable link mechanism 10 and rack-and-pinion gearing 13. The tool T is mounted in a head 3 angularly adjustable on the upper member of compound slides 4, 5, carried by a knee 6. The tool may be driven from an electric motor or otherwise and braking means may be applied to the work. The peripheral speed of rotation may be about 70 feet per minute and the work may perform three complete reciprocations per minute. If the gear to be finished has helical teeth the tool may have straight teeth or helical teeth of such angle as to give the required divergence between the tool and work axes. In a modification, Fig. 10, an external gear may be finished by means of a gear tool k having concavely bowed teeth, the concavity being preferably less than that required for full length bearing so that the contact is localized at a central zone m. The top and root surfaces of the tool may be either straight or concave. In another modification, Fig. 15 an external gear c may be finished by an internal gear tool r having teeth of bowed formation r<2> convex to the tool axis, to a degree sufficient to localize the bearing at a central zone. In the case of helically toothed tools, the grooves which form the cutting edges are preferably helical and normal to the teeth. In another modification straight toothed gears may be finished by a straight toothed tool arranged on a parallel axis and having teeth which are bowed longitudinally so as to localize the bearing between tool and work. Helical gears may be finished in a similar way by a tool having equal and opposite helix angle and arranged on a parallel axis.