Patent GB-415875-A (GB)
Title: Method of and apparatus for cutting gears
IPC: B23F21/28
Filed: 1933-07-07
Abstract: 415,875. Gear cutting. NATIONAL BROACH & MACHINE CO., 11457, Shoemaker Avenue, Detroit, Michigan, U.S.A.-(Assignees of Drummond, R. S. ; 1168, West Boston Boulevard, Detroit, Michigan, U.S.A.) July 7, 1933, No. 19358. Convention date, July 30, 1932. [Class 83 (iii).] Milling-cutters.-In a method of finishing toothed gears, the gear to be finished is run in mesh with a rotary gear-like cutting tool having conjugate teeth provided with one or more grooves to form cutting edges, the axes of the gear and the cutter being arranged at an angle of less than 30 and the gear and cutter being fed relatively to each other in the direction of the axis of the gear. The method may be employed with a machine similar to that used for lapping operations and consisting of an arbor B carrying the tool P and a non-parallel arbor A carrying the work Q. The arbor B is driven, Fig. 5, from a motor C through reduction gearing D, shaft D<1>, and belt gearing E. The arbor A is mounted between head and tail stocks F, G, on a carriage H slidable on horizontal ways 1 of a vertically adjustable slide I, moving on a column J. The column is mounted on arcuate guides K on the bed L so that both the lateral spacing and the angular relation of the arbors may be adjusted. The arbor A may also be slowly reciprocated in an axial direction during the operation by gearing operated from the shaft D<1>, Fig. 5, and consisting of reduction gearing M, crank disc M<1>, link N, rock shaft N<1> and gear N<2>, engaging a rack on the carriage H. The rate of axial feed is varied according to the work diameter so as to give a predetermined feed for each revolution of the work and the extent of the feed is sufficient to cause the cutting edges of the tool to traverse the blank without permitting the gears to pass out of mesh. Reversing mechanism is provided for simultaneously reversing both the axial feed and the direction of the work rotation. For this purpose the motor C may be reversed by a switch O actuated after a predetermined number of motor revolutions. If the work has a movement V<4> which crosses the cutter from left to right, Fig. 5, the axial movement is preferably also from left to right as shown by arrow V<5>. The teeth of the finishing tool are conjugate to the blank teeth, but have a different helix angle so that the arbors A, B are inclined when the gear and tool are in mesh. This inclination lies between 3 and 30 and is preferably 10. To produce the cutting action the tool teeth may be formed with a circumferential groove P<1>, the sides of which are flared outwardly, Fig. 16, at the same angle as that between the arbors A, B. In operation, the head I is moved downwards to engage the gear with the tool with a predetermined pressure and the work and tool are rotated in mesh while the work is fed axially whereupon the sharp edge on one side of the tool groove takes a shaving cut from the work. Various forms of tool may be employed. The flare of the sides of the groove P<1> may be varied and may be either outwards or inwards. In another modification, Fig. 14, the finishing tool has helical teeth each traversed by an oblique groove P<2>. In another modification, Fig. 12, the tool consists of four toothed discs, the outer discs R, R<1> having teeth lying along the same helices and the inner thin discs R<2>, R<3> separated by a spacer disc R' and having a different helix angle from the discs R<1>, R2. Thus a cutting edge S of the disc R<2> lies in the continuation of the surface of the tooth R and forms the cutting edge on one side of the groove while an edge S<1> of the disc R<3> lies in the continuation of the surface of tooth R <1> and forms the cutting edge on the other side of the groove. In some cases the cutting edges may be above or below the corresponding teeth R, R<1> to give deeper or shallower cuts on the work. The discs R<2>, R<3> may be made of tool steel and the discs R, R<1> of cast iron or similar metal. In another modification a number of discs S<1>-S<4> may have the teeth partly relieved at T<1> on one side and T<2> on the other, with unrelieved portions T' thus forming acute cutting edges T<3> on each disc located between unrelieved guide portions T'. In some cases instead of producing pressure between the gear and tool by close lateral spacing a brake may be applied to the movement of the work. Reference has been directed by the Comptroller to Specification 392,385.