Patent GB-476851-A (GB)
Title: Gear finishing tool
IPC: B23F21/28
Filed: 1937-04-16
Abstract: 476,851. Gear - cutting. FELLOWS GEAR SHAPER CO. April 16, 1937, No. 10930. Convention date, April 16, 1936. Addition to 466,330. [Class 83 (iii)] The gear-finishing tool described in the parent Specification is modified by constructing the tool of a number of units assembled in axial alignment in spaced relation, the units being separated for sharpening purposes. In one form a hub 21, Fig. 5, is provided with teeth 23 constituting one tool unit while the complementary teeth are provided on an annulus 24 which is clamped against the part 23 by a ring nut 28. A space 32 of about À006" width is left between the tool units for the egress of chips. The cutters are sharpened by grinding after the units have been separated. The abutting shoulders 30 on the two units may if necessary be ground as the cutters wear to maintain constant space 32. Alignment between the two units may be secured either by a key way or by a setting member engaging a pair of tooth spaces before tightening the nut 28. The teeth may have top rake at their cutting edges as shown at R, Fig. 5. In some cases the cutting edges 231, 251 of spur gear tools may be obliquely arranged, Fig. 9. In a modification, Fig. 7, the tool comprises three units 33, 34, 35 clamped against a shoulder 37 on a sleeve member and aligned by a pin 44 passing through bushings in all the units. The central unit 34 has cutting edges at both ends. Top rake may be provided for each cutting edge. The profiles of the teeth on the tools are conjugate in profile to those of the gear to be finished, the tool and work being mounted on non-intersecting axes whose mutual inclination corresponds to the difference in helical angles of the tool and work gears. Thus, spur gears may be finished by means of helical tools while helical gears may be finished by either spur of helical tools. In all cases the cutting is effected by the relative longitudinal slip between the tool gear and the work. In order to increase the extent of the contact between teeth of a tool gear A and a helical gear B, Fig. 12, the teeth of the tool are of concave bowed form, being broader at the ends than at a central section, as shown in Fig. 10. The curves 23e, 25e are parts of a concave helicoid similar to the opposite face curves 23f, 25f. In the case of a tool for finishing internal gears, the extended contact is obtained by making the side tooth surfaces of convexly bowed formation. Simitar tools for finishing helical gears may have the median lines of the teeth parallel to the tool axis as in Fig. 9. The three unit tools, Fig. 7, also have teeth lying along similar concave or convex curves. In some cases the top surfaces of the tool teeth may either by of longitudinally bowed convex or cancave form to obtain uniform depth of mesh between the tool gears and the work. In another modification, the curvature of the tooth sides may be greater than that required for uniform bearing so that a more concentrated pressure in the region of the cutting edges of the tool is obtained without unduly increasing the total pressure between tool and work. In another modification, the tools may be provided with internal teeth having teeth of longitudinally bowed form. The side surfaces of the tools adjacent the cutting edges give a burnishing action and the cutter or work may be axially moved during operation to perform uniform cutting and burnishing throughout the length of the work gears. The tools and work preferably have incommensurable numbers of teeth so that each tooth of the tool engages all the teeth of the work.