Patent GB-1072237-A (GB)
Title: A method of cutting longitudinally curved and cambered teeth of a pair of bevel gears or hypoid gears
IPC: B23F21/22
Filed: 1963-12-30
Abstract: 1,072,237. Gear-cutting. OERLIKONBHRLE HOLDING A.G. Dec. 30, 1963 [Jan. 7, 1963], No. 51249/63. Heading B3K. A method of cutting longitudinally curved teeth on a pair of co-operating bevel or hypoid gears, the teeth of one gear being differently cambered in length relative to the teeth of the other gear, the teeth of both gears having mean pressure angles of anZ of the concave tooth flanks and αnT of the convex tooth flanks, comprises a continuously indexing self-generating process performed in two separate stages employing for each stage a different cutter head each situated substantially symmetrically relative to an axis (17) and mounted for rotation at a given radius from a central point (M) about a central axis of rotation (13, 18) and each provided with inner and outer cutting edges which are straight and lie in a cutting edge plane, including-in the manner of putting one imaginary crown wheel upon another with the double-sided imaginary crown wheel common to both stages in which the corresponding cutting edge planes or both cutter heads are coinciding with each other-the setting-up steps of: arranging each cutter head with the pitch point plane (25) of one cutter head passing through a pitch point (p) situated on each cutting edge, inclined towards the pitch point plane (30) of the other cutter head, the line of intersection (21) of said two pitch point planes (25 and 30) lying in a common pitch plane (14) and passing through a mid-point (P) of the longitudinal tooth curve when a pitch point (p) of a cutter edge passes at the same moment said mid-point (P), said intersection line (21) being at right-angles with respect to the radial pitch point plane (31) of the cutter head passing at the same moment the same mid-point (P); arranging each cutter head with its associated pitch point (p) situated at a radius rw<SP>1</SP> from the central axis (13, 18) about which it is rotatable, said radius rw<SP>1</SP> lying in the pitch point plane (25, 30) and having a length which is for both cutter heads equal to the projection of a given radius rw which lies in the common pitch plane (14) to the relatively inclined pitch point plane (25, 30), so that the radii of the two cutter heads slightly differ from each other if the said relative inclination of the two heads is not the same; arranging the central axes (13, 18) about which the cutter heads are rotatable in such relation to one another that the angle (#) of the pitch point plane (25, 30) of each cutter head with respect to the common pitch plane (14) is less than 15 degrees and the angle formed between the pitch point planes (25, and 30) of both cutter heads is also less than 15 degrees; wherein the cutters (8, 10) are fixed on the respective cutter head inclined to its pitch point plane at an angle corresponding to the angle at which the cutter head is inclined to the common pitch plane in such a way that a straight line at right-angles with respect to the common pitch point plane forms, except for cutting angle corrections, a mean pressure angle αnT with the outer cutting edges (12, 27) and a mean pressure angle αnZ with the inner cutting edges (11, 26). A pair of bevel or hypoid gears are generated with crowned teeth to reduce the area of contact, the contact being central, or to one end of a tooth. The machine has a sliding headstock 1 carrying a cradle 2 on which a carriage 3 is slidable and carries a cutter head 4 rotatably and pivotally mounted. The work-head 5 is pivotally adjustable. The teeth of both gears are generated on the same or similar machines each in a continuous indexing operation but only the cutting of the tooth of one gear in a central position of a tooth generating cycle is considered. The cutter head 4 has inside and outside cutting edges 12, 11 on blades 8, 10, the pitch point p lying on a circle 9 of radius r w <SP>1</SP> concentric with the cutter head axis 13. The cutting edges 11, 12 lie in planes which cut the plane of the circle 9 in lines 37. The edges lie at the angles of aT and αZ to the lines 33 perpendicular to the lines 37. The mirror-symmetrical positions of the cutter heads 4, 4a, Fig. 1, for cutting the matching gears are shown with their axes 13, 18 intersecting the pitch circle plane 14, Fig. 2, in points C 1 , C 2 , the pitch plane being tangential to the pitch cone of the gear to be cut and containing the two imaginary plane gears 15, 16 represented by tooth curve lines. The angles at which the pitch point planes of the cutter heads are set relatively to the pitch plane 14, may be equal and opposite, of opposite or the same sign but unequal, or one or both angles may be zero. In other words, the teeth of both gears may be crowned, one only may be crowned, or one may be crowned to a greater extent than the teeth of the other are increased in width.