Patent GB-266357-A (GB)
Title: Improvements in or relating to toothed gears
IPC: B23F9/02
Filed: 1927-02-17
Abstract: 266,357. Gleason Works, (Assignees of Wildhaber, E.). Feb. 19, 1926, [Convention date]. Gear-cutting; milling-cutters.-Tapered gears of either bevel or hypoid form are made by a tool having a side cutting-edge whose pressure angle is different from and preferably greater than the pressure angle of the tooth surface to be cut, while imparting rolling generating movement between the tool and blank corresponding to the motion of a cone of different (and preferably greater) dimension from the pitch cone of the blank rolling on the pitch surface of the gear represented by the tool. By this process both sides of the teeth may be cut simultaneously to a form wherein the bottoms of the teeth intersect approximately in the gear pitch cone apex while the teeth are correctly tapered along their length. Fig. 1 shows the application to the cutting of a curved toothed gear 17 by means of a face mill having blades arranged alternately in pairs which cut on opposite side faces of the teeth of the blank, the cutting edges 13, 14 having a different pressure angle, preferably greater, than the pressure angle of the faces 15, 16 of the gear teeth. During the cutting, the rolling of the blank corresponds to the movement of a cone such as 22 which is larger than the pitch cone 20, on the pitch surface of the gear which the tool represents. In Fig. 1, the tool is given corresponding generating movement in the direction of the arrow 28 about the blank pitch cone apex 19. The tool may represent a true crown gear, Fig. 3, in which case the tool axis 29 is inclined to the axis 31 of the imaginary crown gear, or, alternatively, the tool mav represent a crown gear whose pitch cone angle is somewhat less than 90. As the result of using a tool of larger pressure angle than the gear to be cut, the bottoms of the teeth lie on a root cone 40, Fig. 7, whose apex 40' is closer to the cone apex 39 than the corresponding apex 38<1> of the root cone obtained when a tool of normal pressure angle is used. By suitably curving the teeth longitudinally, the bottoms of the toothgrooves may pass through the blank cone apex. In a modification, the annular face mill may be replaced by an annular grinding-wheel. The invention is also applicable to the cutting of gears having teeth which are conjugate to spherical surfaces. In Figs. 8 and 9, the centres of the longitudinal curves 46, 48 lie on a circle 50, the convex tooth surfaces of the crown gear having centres lying on a circle 54 below the pitch plane 52 and the concave tooth surfaces having centres on a circle 55 above the pitch plane. To produce a gear which is conjugate to the crown gear 45 the axis 56 of the tool is inclined to pass through the centres 53, 51 of concave and convex tooth surfaces. The tool is provided with inserted cutting-teeth 62 whose surfaces are parts of convex and concave surfaces respectively having the same radius as the tooth surfaces to be represented and whose centres coincide with the centres 51, 53 respectively. In a modification, the cutter may represent a crown gear having an angle less'than 90. The rolling of the blank as before represents the movement of a cone which is of larger angle than the pitch cone. A machine for producing a gear according to the invention is shown in Fig. 12. The grinding-tool 80 is driven by an electric motor 83 through gearing 84 and both the generating movements are imparted to the blank 85 which is mounted on a spindle 86 and carries a master gear 87 of larger cone angle than the blank and rolling on a fixed crownwheel segment 88. If the gear being produced is the generated member of a gear pair in which one member is non-generated, the pitch cone angle of the segment 88 may be the same as the pitch cone angle of the gear with which the gear being produced is to mesh. The blank spindle is mounted in a carrier 89 which is provided with a gear segment 90 engaging a segment 91 which is oscillated to swing the blank carrier by means of a crank on a vertical shaft 96. After the cutting roll, the blank is withdrawn during the return and indexed. The withdrawal is effected by a cam 100 which acts through a lever 101 and rod 103 to lower the support 106 of the carrier 89 against the pressure of a spring 107. A second spring 109 holds the carrier firmly on its support, and a brake 111 prevents rotation of the blank on the return movement. If desired only one member of a generated pair, preferably the pinion, may be out as above described, while the other member is made in the usual way. In this case, the axis 114, Fig. 9, of the tool employed to produce the latter gear is inclined to the drawing plane at an angle such that the sphere centres 112, 113 of the tool cutting-edges are at the same distance from the apex as the centres 51, 53 are.