Patent GB-736657-A (GB)
Title: Improvements in and relating to means for generating involute gears
Inventor: CLEFF PETER HERBERT
IPC: B23F23/00
Filed: 1953-09-08
Abstract: 736,657. Gear-grinding. MAXWELL, Sir D. C., and PARSONS & MARINE ENGINEERING TURBINE RESEARCH & DEVELOPMENT ASSOCIATION. Sept. 8, 1953, No. 24786/53. Class 83 (3). [Also in Group XXIII] A gear grinding machine-head comprises a grinding wheel 11, Fig. 1, which has a flat or coneshaped operative surface and is mounted in a member 8 movable about a main pivot 6 which is axially normal to and co-planar with the generatrix gg of the face of the wheel and parallel to the gear axis M, the pivot 6 being mounted on a slide 5 in a rectilinear guide 4<SP>1</SP>-4<SP>2</SP> perpendicular to the gear axis and at a distance Ro + a from it, and means for correlating the angular and rectilinear movements so that an angular movement # of the member results in a rectilinear movement a#-Ro sec # (# - sin #), or a high-order approximation thereto of the slide, whereby the said generatrix is also a generatrix of a true or nearly true involute Oi generated from the gear base circle of radius Ro. The head 1, Fig. 10, is mounted on a slide which can be traversed by a screw 67 to carry the grinding wheel across the width of the gear. The member 8 is adjustable about the axis gg for grinding helical gears. The slide 5 is reciprocated by a hydraulic device with a stationary piston fixed to the head 1. Computing the equation. The term a tan # is computed by a link 12, Fig. 2, attached to the member 8, a link 14, a bell-crank 16, 25 pivoted at 17 on an extension 5<SP>1</SP> of the slide 5, and a sleeve 64 which slidably receives the arm 25 and is pivoted at 41 on a bracket 114, the distance 41-17, in the datum position, being equal to a. The mechanism may be replaced by two circular arc segments pivoted on the slide 5 and linked by tapes, the segments being connected respectively to a rod such as 25 and to the member 8; or it may be replaced by two identical slidercrank mechanisms including a common slideblock guided on the extension 5<SP>1</SP>. The term Ro sec # (# - sin #) is computed by moving the pivot 41 either laterally by that amount or, which is equivalent, vertically by an amount Ro cosec # (# - sin #), or by mounting the pivot on a slide 108, Fig. 9, and rotating a turntable 106 to maintain the correct perpendicular distance Ro (# - sin #) of the pivot from its datum position. The two computing mechanisms are combined in an approximating arrangement in Fig. 10, where the sleeve 64 carries a link 57 anchored to an adjustable block 65, the distance between pivots 41, 61 in the datum position being Ro/n. The movement of the pivot is thus Ro/n (1 - cos #) giving an error in the movement of the slide 5 namely It is shown in the Specification that n = 2.8 is a preferred value and gives at some points a negative, and at some a positive, departure from the true involute. For an accurate profile, the link formed by the sleeve 64 is made as a separate link 54 and is mounted on a pivot 42, Fig. 16, on the slide 40. It is then rotated through an angle # defined in by connecting it to a lever 48 to which is pivoted a frame 84 having, at one end, rollers 80, 83 contacting a cam arm and, at the other, a fork 86 engaging a pin 85, the cam arm and the pin being carried on a lever 43 pivoted at 41. The links 54, 57 may be adjustable in length. In a modification, the levers 43, 48 are connected by a pivoted link whose length and pivoting points can be chosen to give a very close approximation to the cam and frame mechanism in the latter embodiment. Modifying tooth profile.-In a further modification, the levers 43, 48, Fig. 19, are connected by the linkage shown, the pivot 73 being eccentric to the pivot 72 and integral with a lever 77 carrying a roller 79 held in contact with a cam 68<SP>1</SP> attached to the slide 40. The cam 681 is shaped to give appropriate profile modifications to the gear teeth. In a further form of mechanism, Fig. 20, a cam 52 on the slide 40 and a follower 51 on an arm 49 modify the movement of the pivot 41 through a double eccentric cam 44, 45. The cam may be designed not only to achieve greater accuracy in generating an involute but also to compensate for any manufacturing inaccuracies in the grinding-head. Other linkages including slider-crank and rolling- tape mechanisms are described for connecting the levers 43, 48. Tooth profile modifications may also be applied by a cam bar on the head 1 coacting with a follower on a lever which rotates an eccentric pivot at 17 carrying the levers 16, 25; furthermore, by moving the cam bar by a further cam bar, the tooth profile modification may vary along the length of the tooth. In a further modification, the movement of a sleeve 90, Fig. 29, in which slides a link 89, is controlled by a straight-edge 91 attached to it and by a cam 94 of radius Ro equal to that of the gear to be ground. The link 89 and member 8 are interconnected by two slider-crank mechanisms with a common slide 102. Generating cams. A mechanism is described for generating the cam arm 43 of Fig. 16, the mathematical basis being A close approximation of the right-hand side of the equation is n (sec #/2. sec #/4. sec #/6.93 - 1). Three levers 204, 207, 208, Figs. 26 and 27, the former of length n, are pivoted at 201, 202, 203 and are connected to each other and a sliding rod 235 by rods and forked ends 209, 218, 227 at right angles to them, the forks engaging sliding blocks. The rod 235 carries an extension 239 on which slides a block 237 pivoted to a lever 240. The resulting relationships are expressed on Fig. 26. The levers 204, 207, 208 are rotated by the correct amounts by tapes and segments 248, 255, 259. The segments are connected to a lever 246a which is linked to the lever 240. As the lever 246a is rotated through an angle #, so the lever 240 is rotated through an angle # and a cam 260 mounted on an arm 244 connected to the lever 240 is ground to the required profile by a grinding wheel 254 on an arm 250 connected to the lever 246a. To generate a double cam profile, the mechanisms of Figs. 16 and 27 are combined, the rollers 80, 83 of Fig. 16 being replaced by grinding wheels.