Patent GB-640641-A (GB)
Title: Improved process and machine for manufacturing bevel gears with curved teeth
IPC: B23F9/10
Filed: 1946-09-17
Abstract: 640,641. Gear-cutting. FRANCIS, E. L. M. (Verwaltungsges. der Werkzeugmaschinenfabrik Oerlikon). Sept. 17, 1946, No. 27902. [Class 83 (iii)] In a process for milling curved teeth in a bevel gear, two cutter discs C<SP>1</SP>, D<SP>1</SP> are set at a predetermined angle to each other which is independent of the pitch of the teeth of the gear B<SP>1</SP> and the pitch is determined without changing this angle by adjusting the speed ratio between the cutter discs and the work with due regard to the number of teeth of the cutter discs and the number of teeth of the gear. A main variable-speed motor 1 drives a shaft 4 connected through bevel and worm gearing to two cutter shafts H and H<SP>1</SP> which are journalled in slides 11, 12 carried by a drum 13, the axis of the drum being coincident with the shaft 4 and passing through .the imaginary cone apex P of the bevel gear. The shaft 4 also drives a shaft 14, through a gear Z if it is required to reverse the spiral of the gears, and a gear 16 on this shaft meshes with a double gear 17, 18 mounted on a spindle 15a carried eccentrically by a worm-wheel 15. From the double gear, other gearing, including a shaft 23 arranged vertically beneath the cone apex P, and pitch-change gears T, takes the drive to a work spindle 30 mounted on a headstock 31 adjustable axially of the spindle on a table 32 angularly adjustable round the shaft 23 so as to set the work-piece B<SP>1</SP> at the required cone angle of the gear. A feed and pitch motor 34 rotates the drum 13 through worm gearing 35, 36 and also, through pitch-change gears W, rotates the worm-wheel 15 and its eccentric spindle 15a. Operation.-The cutters are first adjusted by means of the slides 11, 12 so that their axes are at a distance V from the cone apex. The axes of the cutters are parallel to each other in one plane, i.e. the separating angle between them is 180 degrees. If only the main motor 1 were running, the cutters and the work-piece would be rotated so that each blade of the cutter then in operation would enter successive teeth of the work-piece, each blade forming the curve of the tooth as a result of the movement of the blade across the work-piece while it is rotating. With the motor 34 also rotating, the drum 13 is slowly rotated to give a rolling motion to the cutter disc and one cutter D<SP>1</SP> generates all the convex flanks of the teeth. This motion is equivalent to the rotation of an imaginary crown-wheel A<SP>1</SP>, Fig. 12, meshing with the work-piece and, in order that the cutter blades may still engage in successive teeth of the work-piece, the harmonizing motion is applied to the work-piece through the gears W and the worm-wheel 15. During the first part of the roll of the drum 13, only the cutter D<SP>1</SP> operates and, during the latter part of the roll, the cutter C<SP>1</SP> comes into operation and forms the concave flanks. The two cutters may also be arranged with the spacing V zero, so that the blades of one cutter engage in the spaces between the blades of the other and so that the operative blade of one cutter follows the operative blade of the other into the same tooth notch of the work-piece. By circumferentially adjusting the two cutters relatively to each other so that the edges of the blades working in the same notch are closer together or wider apart than half the distance between two successive blade cutting edges, it is possible to vary the thickness of the teeth. If the two blades are wider apart, the blade working on the second flank starts cutting after half the pitch is completed so that the notch is made wider and the tooth thinner. In order to make this adjustment, a pair of adjustable toothed clutch discs are fitted in the drive for one of the cutter shafts. Rounding and barrelling.-By arranging the blades of the cutter D<SP>1</SP> for the convex flanks so that the cutting edges are at an angle of 90 degrees - α, Fig. 11, to the cutter axis, more material is removed at the ends of the gear teeth and the teeth are rounded.