GB400581A - Toothed wheel and method and machine for the production thereof - Google Patents

Abstract

400,581. Toothed wheels. FORSTER, A., 61, B÷ndlerstrasse, Kilchberg, Lindenberg, Switzerland. March 15, 1932, No. 7681. Convention date, March 17, 1931. [Class 80 (i).] In a toothed wheel A particularly suited to high speed mechanisms, the arc of contact e, g, is considerably less than the pitch, and continuity of contact between a pair of gears is maintained by curving the teeth longitudinally as shown in Fig. 2, wherein the height K of the curve of the developed tooth directrix is at least equal to the difference between the pitch t and the length of the arc of contact, and the zone of contact moves axially along the gear. In some cases the path of contact is reduced almost to nil, the height K being then at least as great as the pitch. The tooth profile p, Fig. 3, is of involute form generated from a base circle Kg. p being the pitch point, c d the active profile and alpha the pressure angle. Conjugate gears a, a<1>, Fig. 6, have toothed directrices s s<1>. In one modification, Fig. 7, only the dedendum c p of the profile follows an involute curve p<1> which is conjugate to an involute p<2> of an imaginary mating gear, while the addendum pd lies within the involute. In this case contact between pairs of gears is limited in theory to the pitch point p and there is no slip between the engaging tooth flanks. The tooth directrices s are of cycloidal or modified cycloidal form and are generated by straight sided rotary cutters mounted in a cutter head which is driven in timed relation with the work spindle to produce the cycloidal tooth form. The usual rolling-generating movements of the cutter and work are superposed on the cycloid producing movements. According to the invention, a pair of cutters F1, F2 are used for cutting one face of a tooth and another pair of cutters for the opposite face thereof, the cutters being mounted on milling heads connected with the work spindle. The cutter F2 having the normal pressure angle alpha generates mainly the middle part of the tooth flank while the cutter F1 inclined at the smaller pressure angle generates mainly the end parts of the flank, Fig. 15. The errors between the profile thus produced and the theoretical profile may be minimized by reducing the pressure angle alpha The invention is also applicable to the cutting of bevel wheels, the axis of rotation of the cutter spindles being inclined at the required angle to the bevel gear axis and the angular velocities of the cutting edges being periodically varied to obtain the desired pitch variations between the small end and the large end of the bevel gear teeth.