GB514530A - Improvements in or relating to gear cutting tools - Google Patents

Abstract

514,530. Milling cutters, NATIONAL BROACH & MACHINE CO. May 9, 1938, No. 13793. Convention date, May 10, 1937. [Class 83 (iii)] A gear finishing tool 10 of the rotary intermeshing type in which the teeth 11 have grooves or serrations 12 forming cutting edges for removing shavings from the work, the grooves or. serrations are wholly or partly converged inwardly to the base of the groove. In Fig. 3, which shows a section of the tooth. the end land 14 is preferably wider than the intermediate lands 15. The grooves have inwardly tapering side walls 16, 17, the cutting angle adjacent the land 14 being a right angle and the edge at the top of wall 16 being equal to a right angle plus the helical angle of the tooth. An acuteangled cutting-edge which is normally effective in one direction of cutting is thus avoided. The land thickness may be À026in. and the groove width - 053in. at the top and 029in. at the bottom, and the groove depth 050in. The helical angle and inclination of side wall 17 are each 27 degrees in this cutter. The width of land is increased and the width of groove decreased by grinding to sharpen the cutter. In a modification the acute angle is avoided by a chamfer 18 which may form either a right-angled or an obtuseangled cutting-edge. The chamfer is of sufficient width to provide for a number of regrinds of the tool. In another modification the side walls are inwardly inclined near the bottom of the groove to strengthen the land portions. In another modification the strengthening is effected by rounding off corners at the bottoms of the side walls. In a further modification, Fig. 7, this rounding off at 20 is combined with an inwardly tapered side wall 17. The roots of the teeth may be axially undercut as described in Specification 474,227, the oil stream when the cutter is in use serving to wash away cuttings through the undercut grooves. In manufacture the tool is first finished to shape, then the grooves are cut, the cutter heat-treated, and the lands finally finished by grinding. The Specification as open to inspection under Sect. 91 describes also a modification, Fig. 10 (Cancelled), in which the undercut is as shown at 13<1>. Other shapes of undercut may also be used. This subject-matter does not appear in the Specification as accepted.