GB238935A - Improvements in or relating to gear cutting machines - Google Patents

Abstract

238,935. Saito, M. May 26, 1924. Gear-cutting; milling-cutters.- Bevel gears with curved teeth are cut by means of a taper or cylindrical hob of variable pitch, the curve of the hob teeth being such that the development on a plane surface may be expressed by the equation :-y = Ax<2> + Bx + C in the case of a cylindrical hob, or @ = A<1># + B' log p + C' in the case of a taper hob. Fig. 1 shows the relative positions of a hob 2 blank 3 and the imaginary crown wheel 1 which the hob represents. From the speed relations which must exist between the rotation of the blank and hob it is shown that the angular velocity v of the hob is given by v = - (V<1> - v<1>/sin@) where n = no. of threads on hob, N<1> = no. of teeth on blank, V<1 >= Angular velocity of blank on its axis, v' = Angular velocity of blank relative to hob about the axis 0, @ = cone angle. of the blank. In Fig. 3 the X axis is the trace of the plane containing the hob axis and perpendicular to the crown wheel plane, the line FG denoting a tooth on the crown wheel and 4 the developed tooth of a hob. FH being the common tangent. From the condition that this tangential relation must exist at all points along the hob it is shown that the equation of the line 4 is y = 1/2R x<2>- @N/Rnx, where R = length of line O E, r = radius of hob pitch cylinder. The Specification also describes the cutting of gears by means of a cutter having a conical pitch surface, and it is shown that in this case the developed curve of the hob teeth may be expressed by the equation @ = A<1> @ + B<1> log p + C<1>. A machine for cutting gears according to this method is shown in Figs. 5 and 0. The hob spindle is mounted in a member 8 and can be secured in the desired angular position on a slide 9 which is rotated about the axis O O<1> to give the angular movement v<1> to the hob by means of a pinion 11 engaging a toothed sector and driven from the pulley 12 through shaft 18, reversing change gears 20, shaft 22, and worm gearing 21. The hob spindle is also driven from the pulley 12 through shafts 13, 14, differential gearing 25. shaft 15, reversing bevel gearing 27, and shaft 17. The planet member of the differential gear is driven from a shaft 23 which is connected by change gears to the shaft 22 to compensate for the rotarv movement of the tool head. The shaft 31 of the hob-driving train is connected by change-gears to a shaft 32 driving through the gearing shown in Fig. 5, a worm-wheel 39 on the spindle carrying the blank 3. The blank holder 37 is angularly adjustable about the axis O 0<1> so that the blank may be adjusted to a position corresponding with the central line O C<111> in Fig. 1. the teeth being completely formed by movement between the positions O C' and O C". Specifications 208.177, 220,027, 230,884 and 230,885 are referred to.