GB801289A - Method of shaving conical involute gears - Google Patents

Abstract

801,289. Gear-finishing; milling-cutters. NATIONAL BROACH & MACHINE CO. Dec. 6, 1956 [Jan. 30, 1955], No. 37317/56. Class 83 (3). A method of shaving a conical involute gear G consists in meshing it with a conical involute cutter C, the wide ends of the cutter teeth being adjacent the narrow ends of the gear teeth and the axes being parallel to a reference plane and crossed at 3 to 30 degrees, and effecting a relative traverse in a direction parallel to the plane, and perpendicular to the gear axis. The gear may be cut initially by a hob traversed in an inclined path, or by a relative radial in-feed during traverse. The blank may be cylindrical and the finished gear have teeth of decreasing depth, or may be conical and have teeth of constant depth. In each case, pairs of such gears will mesh correctly when engaged either way round; if big ends mesh, there will be point contact only between the teeth, but, if each big end meshes with a small end, line contact ensues. If a conical involute gear is shaved by a cylindrical cutter, a hollow lead modification is produced. By shaving a gear G with a helicallytoothed conical involute cutter C, correct teeth are produced. The cutter may be hobbed on the same fixture as the gear and have the same cone angle-say 7¢ degrees. The cutter teeth have serrations perpendicular to the cutter axis and extending helically round the cutter, and the root clearance grooves 33 are conical. A pressure angle of 22¢ degrees is used. The gear or cutter is rotated to give a surface speed of 250 ft./mm. and traversed from a position of loose mesh, through the position of minimum centre distance, to a second position of loose mesh, in a direction at right angles to the gear axis; the gear may then be fed to put on cut before the directions of traverse and rotation are reversed, and the gear and cutter returned to their initial position. Initially, the gear may be fed into tight mesh with the cutter and then traversed to its initial cutting position, and the gear then elevated to put on cut prior to the relative rotation and traverse. The teeth of the gear may be modified by providing an opposite modification on the cutter teeth. A further modification results if the angle of traverse is slightly offset from the perpendicular, because the gear is then moved into tighter mesh with the cutter due to the taper of the teeth, thus resulting in the teeth of the gear being more heavily machined at the ends which are in engagement at the end of the traverse. By decreasing the cone angle of the cutter, an increasing amount of hollow lead may be produced, the cutter and gear then being meshed with their axes slightly inclined at an angle equal to the difference in the cone angles. Regrinding of the cutter reduces the operating pressure angle and increases the operating cone angle. Specifications 635,020 and 672,022 are referred to.