Patent GB-563777-A (GB)
Title: Method and apparatus for generating toothed gears
IPC: B23F5/02
Filed: 1943-02-26
Abstract: 563,777. Gear-cutting. FELLOWS GEAR SHAPER CO. Feb. 26, 1943, Nos. 3206 and 3207. Convention dates, Feb. 10, 1942, and Feb. 12, 1942. [Class 83 (iii)] In a method of and apparatus for generating gears, the gear blank, such as A, Fig. 5, is rolled without slip on a curved pitch line represented by an internal gear having its centre at B. the pitch line itself being rolled as on a rack R represented by a pair of plane-faced grinding wheels or other tools T, T<1>. Thus, a number of blanks W<1>-W<6> are rolled under the control of master gears engaging an internal gear with teeth Gi arranged coaxially with an external gear, teeth Ge, rolling on the rack R. Two stages in the generation of involute teeth by this combination of movements are shown in Figs. 6 and 8, it being assumed that the gear assemblage rolls on the rack to right (rotation in direction of arrow a, Fig. 5) while the work gears move orbitally in the opposite direction (arrow a<1>) resulting in a rotation in direction of arrow a<2>. It is also assumed that the components a and a<1> are equal so that the movement of the gear axis being indicated by the points A and A<3> in Figs. 6 and 8 respectively, the axis B moves the same distance in the same direction and the pitch circle P<2>, C<2> of the gear blank remains in contact with the pitch line P<1>, C<1> of the rack represented by the tools. In a machine embodiment, the orbital movement is preferably rapid and unidirectional, while the rolling is slow and is reversed periodically and complete generation of all the teeth is effected only after a considerable number of orbital rotations. A base 11 has uprights 12, 13 supporting a slidable carriage 16. The grinding-wheels are located beneath the carriage in housings 19, 20 and are driven by hydraulic motors 22, 23. The mounting and adjustment of the grinding-wheels for finishing either spur or helical gears may be as described in Specification 554,115. The work carriage includes a central shaft 26, Fig. 18, supported in outboard members 27, 28, suspended from bars 29, 30. The shaft 26 has keyed thereto a headstock carrier 31 and tailstock carrier 32 between which are located the work spindles 37 carrying the blanks W<1>-W<6>. Adjusting hand-wheels 41 are provided for the tailstock centres 36. Rotation is imparted to the shaft 26 to give orbital movement to the blanks by means of an hydraulic motor 43 which drives through a yieldable rubber coupling 46 to absorb vibration. The work spindles carry master gears 47 meshing with an internal gear 48 and preferably having the same number of teeth as the work gears. The internal gear Ge of Fig. 5 is represented by a cam 51 having involute faces 52, 53, Fig. 3, which coact with abutments 54, 55 representing the rack R and having a limited range of pressure angle adjustment. The abutments are secured to holders mounted on slides 61 moved to or from each other by a right- and left-hand threaded spindle 63. The carriage 16 is reciprocated by an hydraulic cylinder, the reversal being controlled by dogs on the carriage. During this movement the former reacts against the abutments to impart rolling movement to the gear 48 on the theoretical rack. The abutments may be displaced by screw 63 to apply depth feed to the work. In some cases the machine may have different work-spindles arranged at different distances from the central axis B so that gears of different diameters may be finished in one operation. In another modification, a singlespindle machine is arranged to finish gears one at a time. In this form, Fig. 12, the internal gear may: be only slightly larger than the master gear 47 and gear W being finished and high speeds of revolution may be employed. The number of teeth of gear 47 is preferably prime to that of the gear 48. Alternatively, indexing mechanism may be employed. In this form, Fig. 18, each spindle is coupled to its master gear through an index plate 80 coacting with a carrier plate 81 and pawl. A hydraulic, torque motor supplied by passages 92, 93 operates the indexing mechanism. The pawl has a tail which during the orbital movement is engaged by a stationary dog 100 on the bar 30, thus lifting the pawl momentarily and allowing the torque motor to rotate the spindle and index plate one tooth relatively to the master gear. A modified arrangement of this type of indexing mechanism is also described. In another modified form of indexing mechanism, a brake device is provided to retard the spindle when it is uncoupled from its master gear, the brake shoes 106, Fig. 22, being actuated by hydraulic pressure through a line 108. In all modifications, the abutments engaging the cams may be angularly adjusted to generate different face curves on the teeth. Thus, if the abutments are set at an angle to the median line of n<1>, Fig. 16, which is smaller than the pressure angle setting n of the grinding wheels, it is shown that the gears generated will mesh with mating gears at a pressure angle n<2> greater than n and the teeth are generated from a smaller base circle b<2>, c<2> than the normal base circle b, c. Similarly, if the angle n<1> is greater than n, the teeth generated will have pressure angles smaller than the normal. In another modification, a single grinding wheel having a pair of conical faces operating on opposite sides of the same tooth space may be used,