Patent GB-677321-A (GB)
Title: Process for gear-cutting
IPC: B23F9/10
Filed: 1947-01-02
Abstract: 677,321. Gear-cutting. PICANOL, J. Jan. 2, 1947 [Jan. 31, 1942], No. 13467/46. Class 83 (iii). In a process for generating bevel, hyperboloidal, crown, and face gears, a rotary cutter is mounted on an axis offset relatively to the blank axis and each tooth of the cutter has only one cutting face with relieved cutting edges, each face representing a different transverse section of each of the successive teeth of a gear mating with the one being cut, all the cutting teeth being extended along a spiroidal curve and the cutter and blank being rotated around their respective axes at speeds inversely proportional to the member of the teeth of the blank and its mating gear while progressively giving a feed motion to the cutter in the direction of the tooth depth of the blank only. The process of generating is shown by considering a gear-wheel x, Fig. 1, meshing with a pinion g and arranged with offset axes. A profile h, k, n obtained by the intersection of a surface a with the flanks and top of a tooth b on the wheel will trace out a zone on the pinion as the wheels intermesh, if the tooth b consisted of a number of profiles such as h, k, n parallel to one another and extending along the whole length of the tooth, a complete tooth space of the pinion would be covered during rotation. Thus, if the pinion g be replaced by a blank and wheel x is given a series of cutting faces as above and is fed progressively into the blank, with the cutter and blank rotating in the correct ratio, teeth will be cut on the blank. Such a cutter x, Fig. 13, is mounted in a machine on an offset axis relative to a blank g and the cutter and blank rotated in the correct speed ratio, the cutter being gradually fed into the blank in the direction of the arrow. Milling-cutters.-One form of cutter x, Figs. 15 and 16, is shown in plan and elevation respectively, and comprises cutting faces 2, 2<SP>1</SP>, 2<SP>11</SP>, extending along a spiroidal curve 3, the pitch of which is made nearly equal to the length of the pinion tooth to be cut. The cutter teeth 1, 1<SP>1</SP>, 1<SP>11</SP> are obtained from portions of the basic gear teeth, (shown in broken lines), which would mesh correctly without clearance on offset axes with the pinion to be cut. The ratio between the teeth of cutter and pinion required is chosen so that a cutting tooth does not pass again in the cut which it has made on a given flank &c., until all the other cutter teeth have operated. The cutting teeth may alternatively be directed towards the interior of the cutter and may be of varying width. The cutter x, Fig. 16, completes the cutting in one operation, but, more than one cutter may be used with varying widths of teeth and with various reliefs to give different degrees of bearing for the pinion being cut and finer degrees of finish. The arrangement of the cutting teeth may be so adapted that the cutters may still be used to generate the same pinion after a number of re-sharpenings. Builtup cutters may be employed; one example of such a cutter, Figs. 24 and 23, in plan and sectional elevation respectively, comprises cutting teeth 1 with a base section 9 of trapezoidal form held in a circular recess 11 formed by an outer ring 12, an inner ring 13, and a circular base 10. Thrust pieces 14 tightened by screws 15 and arranged in guides which give the correct inclination to the teeth, maintain the latter in position. The Specification as open to inspection under Sect. 91, describes cutters for superfinishing which take only a small cut and may be built up from a number of laminations, or may be of integral construction with a large number of grooves formed in the tooth flanks. This subject-matter does not appear in the Specification as accepted.