Patent GB-392385-A (GB)
Title: Improvements in method and means for machining gears
IPC: B23F21/28
Filed: 1932-07-28
Abstract: 392,385. Gear-cutting. MICHIGAN TOOL CO., 7171, Six Mile Road East, Detroit, Michigan, U.S.A. July 28, 1932, No. 21288. Convention date, July 31, 1931. [Class 83 (iii).] Tools; milling-cutters.-A gear - finishing machine comprises a cutting-tool of rack form provided with spaced cutting edges along the flanks, the rack being adapted to mesh with the gear blank and to be angularly disposed in relation to the gear axis so that relative longitudinal movement of the rack over the gear is accompanied by lateral slippage between the gear and rack to cause the cutting of the gear. In Fig. 1, the cutting tool comprises a body 41 recessed longitudinally to receive a number of centrally bored cutting elements 45 which are clamped together by a bolt 52. The bottom of the recess in the cutter body is provided with lands 46 and one side of each cutter is sloped at 42 to coact with a longitudinal retaining wedge 56 which is forced downwardly and secured by a number of screws 57. The cutters are mounted between endplates 48, 49, the former having a sloping surface engaged by a wedge member 61. Each cutter has a cross section, Fig. 4, substantially of rack tooth form, and the flanks are provided with a number of cutting edges produced by forming a number of grooves 69 in the tooth surface. For gears other than involute, the profile of the cutter may be modified. Alternatively, the grooves in the cutter flanks may be diagonally arranged as shown in Fig. 5, this construction producing a gear of modified profile. The tool shown in Fig. 1 is adapted for the production of spiral gears which are first roughed out by hobbing &c., and then mounted on an arbor 65, Fig. 15, which is gradually fed downwards by a hand-wheel 70 while the tool is reciprocated on a slide 66. The lateral component of the motion between the tooth surfaces of the tool and gear causes the cutting edges of the tool to remove metal from the gear teeth until the required tooth form is reached. A brake is applied to the gear during operation. The inclination of the arbor may be adjusted to cut gears of different spiral angles. For cutting straight spur gears, the cutting elements are arranged diagonally in the cutter body, Fig. 7; the end block 76 being correspondingly formed. The cutter arbor is then arranged with its axis parallel to the flanks of the cutter teeth, the required lateral component for the machining of the teeth being obtained as before. In place of the built-up type of cutter integral cutters may be employed and in some cases the serrated teeth may be arranged round the periphery of a circular cutter. In a modification, Fig. 18, two cutters may be arranged on opposite sides of the blank and the blank may be moved laterally of the cutters by means of a screw 79. In this way the blank is moved from a cutting portion 45 of the cutters on to a parallelly - arranged burnishing portion 81, the two portions being arranged as shown in Fig. 11. One of the cutting tools is driven to rotate the gear and reciprocate the other tool and the tools are moved towards each other during operation. After the hardening operation, the plain cutting teeth may be used for a lapping operation by introducing a suitable lapping compound between the cutter and gear teeth. In another modification the cutting teeth shown in Fig. 1 may be replaced by plain burnishing or lapping teeth. In another modification, Fig. 20, a number of gears arranged on a single arbor may coact with cutters built up either of single extended blades or from a plurality of aligned cutters. In another modification, Fig. 21, a number of circular tools are arranged round a single blank, one of the cutters being driven at 87. The blank arbor is resiliently mounted and the tool 85 is moved downwards until both tools penetrate the blank to the required depth. More than two circular cutters may be arranged in a similar way round the blank and the cutters may be of the same diameter or they may be of different diameters and different pressure angles. The cutting edges of the cutters may be produced by slotting the teeth completely through, Fig. 25, or by cutting serrations, Fig. 26, which may be undercut to provide the required cutting angles. Other methods of shaping the cutting edges are described. In another modification, Fig. 30, the cutter tooth profile may be formed with a portion 99 which modifies the theoretical profile of the generated teeth as shown in Fig. 31 at 100. In a further modification of a circular type of cutter, the cutter is built up of a number of thin gear-shaped laminµ 123, Fig. 33, keyed to a hub 116 and separated by spacer discs 124. The Specification as open to inspection under Sect. 91 states that roughly hobbed teeth may be produced with the addenda relieved as shown in Fig. 31 by means of a hob having teeth 104 as shown in Fig. 35 (Cancelled), wherein the true hob profile is indicated in dotted lines. The teeth of a pinion cutter for roughing out may be similarly modified. This subject-matter does not appear in the Specification as accepted.