465,008. Gear - cutting. SOC. INGRANAGGI MAMMANO, and MAMMANO, B. Feb. 4,1936, No. 3369. [Class 83 (iii)] A face-mill cutter for cutting curved-tooth bevel gears by continuous generating comprises two finishing teeth or blades arranged at 180‹ the external cutting edge of one tooth being at substantially the same radius as the internal cutting edge of the other tooth, other subsidiary teeth being located between the finishing teeth at different distances from the cutter axis. In considering a crown wheel rotating about its centre O, Fig. 1, in direction of arrow I and a cutter rotating in the direction of arrow II, the crown wheel may be regarded as stationary while the cutter axis moves along the chain line in the direction of arrow III. If A . B and C . D represent the pitch plane intersections of two adjacent gear teeth formed by cutterteeth U2 and U8 disposed at 180‹ on the cutter, Fig. 2, then between the passage of the tools U2, U8 through the work the cutter axis moves from P2 to P8 so that the tooth U2 cuts the concave face with its outer edge and U8 cuts the convex face with its inner edge. An intermediate tooth U6 will have a centre at P6 and its radius must be such that its path either coincides with path C . D or lies within the space cut by the tooth U2. According to the invention the finishing teeth V . W Fig. 5, corresponding to teeth U2 . U8 in Fig. 2, are located at 180‹ on the cutter face and are so arranged that the external cutting point of tooth V has the same radius as the external cutting point of tooth W so that the convex and concave tooth flanks are similar. Subsidiary teeth are arranged as shown over an angle # about 45‹ and not greater than 60‹. These subsidiary teeth may be arranged behind the tooth V and before the tooth W so that every tooth is at a greater radius than the preceding one. For cutting the mating gears the blank is oppositely rotated during the cutting operation and the subsidiary teeth are arranged in advance of tooth V and behind the tooth W so that the radii progressively decrease. If # is the angle subtended between the finishing tooth and one of its subsidiary teeth and the corresponding angle turned through by the blank then gamma = #/2pr where p is the diametral pitch at the small end and r the small pitch cone radius. From this the different radii, Fig. 3, at which the teeth V, S must revolve in order that the paths may coincide at the small end M can be calculated. In this case the pitch plane thickness of the teeth may be equal to the half pitch of the teeth to be cut at the small end. The radius of any subsidiary tooth is obtained from the formula gs<2>=f<2>+r<2>-2fr cos (#Œgamma) where f is the distance of the cutter axis from the work axis and other dimensions are as shown on Fig. 3. A geometric method of finding the radii of the subsidiary teeth is also given and it is shown that if the angle r is small the difference between the radii of the cutters is #/2p so that the spiral of the tool is in this case an archimedean spiral. In this case the cutters must be of less thickness than the small half pitch. If the path A...B, Fig. 9, is the path of the external finishing tooth with centre P then any subsidiary teeth must describe a path A . B2 lying in the tooth space + so that it must have a greater radius than the finishing tooth and by similar reasoning a tooth subsidiary to an internal finishing tooth must have a smaller radius than its associated finishing tooth. The teeth are therefore arranged as shown in Fig. 5. In making the cutter, Fig. 10, the periphery R.S.K.J. of the cutter block follows as a spiral curve determined as described above and the teeth are secured against this curve by key members K1, bolts E1, and nuts Z1. The finishing teeth V1, X1 are at 180‹.