Patent GB-168612-A (GB)
Title: Improvements in gear and rack cutting machines
IPC: B23F1/04
Filed: 1920-03-09
Abstract: 168,612. Greenwood's Standard Gear Cutting Co., Ltd., Greenwood, E. P., and Greenwood, E. March 9, 1920. Gear-cutting; broaching; tools.-A gear-cutting machine for form-shaping racks and both internal and external spur gears embodies means whereby spur gears may also be cut on the generating principle. A vertically adjustable slide 2, Fig. 2, carries an horizontal slide 3 reciprocated by pin- and-slot mechanism from a shaft 8 worm driven from the driving-shaft 11. A turret tool-holder 14 supported in an opening in the slide 3 accommodates rows of cutters of various pitches, any rowof which may be locked in operative position. For internal gear-cutting where only a short stroke is permissible, each row may have a single cutter. The bed 17 carries a dividing-head 18 connected by a stay 20 to a loose head 23, Fig. 1, on a second bed 22. The loose head mav be tilted as shown in Fig. 3 to position the blanks on the spindle 21. The blanks are moved towards the turret to give a progressive feed during the cutting stroke, and are then withdrawn. This is effected by means of a cam 29, Fig. 3, driven fron the main shaft and coacting with a roller 41 to impart motion to a block, in which is secured by collars the plain end of a screw 43 passing through a nut 44 on the blank carrier. At the end of the cutting-stroke a step on the cam allows a spring to withdraw the blanks from the cutters. Provision is made when cutting internal gears for the reversal of the blank feeding and withdrawal motions. A finely-divided wheel 51 is feathered to the end of the spindle 43 so that fine adjustments of the cut may be made by hand. After each complete rotation of the blank, cutting feed is automatically applied until the required depth of tooth is attained. This is effected by a stud 57 on the dividing worm-wheel, Fig. 1, which through lever-and-pawl mechanism operates a ratchet-wheel on a shaft 62 geared to the feedscrew 43, the pawl being automatically made inoperative at the required point by a dog on the wheel 66. The blanks are divided by means of a toothed segment 75 on the main shaft 8, which at every revolution rotates a pinion 76 geared to the dividing-worm 87 carried in a swivelling bracket 88, a locking-device actuated by a cam 74 ensuring that the pinion 76 is rotated exactly one revolution at each actuation. For rack-cutting, the blanks are mounted on a slide 103, Fig. 3, on a bed 104, and a screw 92 in a block 91 passes through a nut on the vertical slide 2. In this case a cam 96 is adapted to force the sliding block downwards to apply progressive feed during the stroke, the return movement being effected by a spring 93. The slide 103 is operated by a screw 105, Fig. 4, and the spacing-mechanism is driven from the dividing-worm shaft 79, Fig. 1, through skew gears 123, 124 and suitable spur gearing, provision being made for cutting teeth with either circular or diametral pitches. Quick return of the rack table is effected by an adjustable dog 125, which trips a lever 126 to shift a clutch member into engagement with a rotating shaft 129 connected by chain gearing to the feed-nut 106, Fig. 4. At the end of the return movement the lever 126 is restored by another dog to its initial position. During this movement the vertical motion of the slide is automatically suspended by means of lever mechanism operated from the lever 126 to shift the cam-roller 95, Fig. 3, on to a concentric portion 140 of the cam 96. At each reversal of the rack-table, an arm on a vertical shaft 147 operates a ratchet device geared to the spindle 92 to impart cutting feed. Hand adjustment of the feed may be made by a hand-wheel 155. The cutters may be made to span one tooth space, or alternatively multiple tooth cutters may be used. For large gears roughing-cutters cutting alternately on opposite sides of the tooth space and mounted as shown in Fig. 13 may be used. In a modified dividing-mechanism for spur gears, a ratchet-wheel mounted on the blank-spindle may be operated through lever mechanism by the to-and-fro movements of the dividing-head. For generating spur gears, a row of multiple racktooth cutters is employed. In this case, the cam 96 operating the vertical slide is of a shape suitable for the pitch to be cut, and the dividing- mechanism is so arranged that during the cutting-stroke the blank is rotated through one tooth space while the cutters are moved through a corresponding distance tangentially, the radial feed during the stroke being operated as before from the cam 29. On the return stroke, the cutters are restored to their initial position while the blank remains stationary. The vertical cutter movement may be obtained also by moving the horizontal slide over a wedge fixed to the bed. In another arrangement, Fig. 10, the vertical movement is derived from a cam 170, and the cutters are fed during the working stroke by a cam 180 which causes the cutter-carrier to swing on its pivot 173. The blank is rotated by means of a pawl 158b co-operating with a ratchet-wheel 157 on the blank-spindle. Instead of the cutter mounting shown in Fig. 10 the turret tool-holder may be constructed with two diametrically opposed slots holding generating-cutters of different pitches.