Patent GB-489686-A (GB)
Title: Improvements in or relating to gear cutters
IPC: B23F21/22
Filed: 1937-12-17
Abstract: 489,686. Grinding face - milling cutters. GLEASON WORKS. Dec. 17, 1937, No. 35000. Convention date, Feb. 11. [Class 60] [Also in Group XXII] A blade for a face-mill gear-cutter, such as those used for cutting spiral bevel and hypoid gears, has a relieved side surface which is of involute helicoid form. The invention may be applied to cutters having inserted blades such as 15, Figs. 2 and 5, or to segmental type cutters or to integral cutters. The blade 15 has an acute-angled inside cutting-edge 18. The top surface 19 and non-cutting side surface 21 may be relief-ground in any known way, but for relieving the cutting side 20 the blade is mounted in a slot 26 of a head 25 similar to the actual cutter head and the involute helicoid of which the surface 20 forms part is such as would be generated by a line in a plane 29 rolling around and moving axially along a cylinder 30 concentric with the head axis 28. The surface thus has a straight line generator in any plane 29 tangential to cylinder 30. Also a plane perpendicular to the axis 28 intersects the surface 20 in a line which is part of an involute of the circle intersection of such plane with the cylinder 30. In one form, the blades 37, Fig. 7, are ground by a rotary grinding-wheel 35 whose side surface 36 is bevelled at the required pressure angle and whose axis 38 is parallel to the blade-holding head axis 39. The head is uniformly rotated on its axis and at the same time moved relatively to the wheel along its axis. On account of the helical motion the contact between the wheel and the blade is along a straight line 44 which generates a helical involute surface and lies in a plane 45 tangential to a cylinder 46 concentric with the head axis 39. The surface of an outside cutting blade may be similarly ground by a conical grinding-wheel of the required pressure angle. A plurality of blades may be mounted in the head and the required relieving motion imparted as each blade passes the wheel. In a modification, Figs. 8 and 9, the blades may be ground by a cylindrical grinding-wheel having an inclined axis 66 lying in a plane parallel to a radial plane of the head and tangential to cylinder 69. The head is as before rotated on its axis and moved relatively to the wheel along its axis, the involute helicoid being generated by a line 72. The outside surfaces may be ground by a similar offset grinding - wheel. In another modification, Fig. 11, a wheel similar to that shown in Fig. 7 is arranged on an axis 83, which is offset from a horizontal plane 86 containing the blank axis, the generator of the relieved surface being shown by line 92. In this form the conical cutter may have an angle less than the pressure angle, and have its axis inclined in the plane 85 to give the required pressure angle to the blade. Blades relieved by these methods are of slightly curved profile in radial planes of the cutter head, but if truly straight profiles in radial planes are required, the grinding-wheels may have very slightly curved profiles concave for inside surfaces and convex for outside surfaces. The relieving may also be effected by arranging the blades helically on a rotary head and imparting a continuous axial movement as the blades pass the grinding-wheel.