Patent GB-325520-A (GB)
Title: Improvements in means for producing worms or cylindrical cams
IPC: B23F23/12
Filed: 1928-11-20
Abstract: 325,520. Kent, Ltd., G., and Douglas, J. G. Nov. 20, 1928. Lathes; rotary chasing cutters.- A lathe is designed for producing worms or helical cams 1, Fig. 13, of variable pitch for co-operating with a conical pin or roller 2 on the rocker arm 3 of a steering gear, the worm being so designed 'that equal angular movements thereof impart equal oscillations to the rocker .arm in any position of engagement. The worm is cut by one or more tools mounted on a holder rotated in a plane parallel to the axis of rotation of the work and the tools are rotatable in the holder and are controlled so as to present their cutting edges at right angles to the helix of the work throughout their engagement. In one form the lathe comprises a headstock 6, Fig. 1, and tailstock 7 between which is mounted the work 5. A transverse slide 10 carries a rotatable shaft 8 passing under the work and driven from the headstock-spindle through change gearing 12, flexible shaft 13 and bevel gearing. A disc 11 secured to the shaft has one or more tools 20 rotatably mounted therein at a radius equal to the radius R, Fig. 13, of the rocker arm 3. When one tool only is used it is maintained at the correct cutting angle relatively to the helix of the worm by means of a link 21 secured thereto and pivoted at its other end to a disc 19 on a radius equal to R, the disc 19 being rotated by gearing 17 from the disc 11 at the same speed and in the same direction. When more than one tool is used the first one cuts the left flank of the helix, the second one the root and the third one the right hand flank, this series being repeated if desired in succeeding apertures of the disc 11, and all the tools are geared by idle pinions to each other and to the tool secured to the link 21. In a modified construction for use when the radius R is too small to permit the shaft 8 to pass under the work, the tools are secured in holders 30, Fig. 5, to which are secured pinions 32 geared by idlers 33 to a central wheel 35 on a shaft 36 passing through a spindle 37 on which the disc 11 and a cover plate 31 are mounted. The spindle is rotatably supported by bearings 29, Fig. 4, on the slide 10 and is rotated by a bevel gear 16 from the lathe spindle while the shaft 36 is maintained stationary by an arm 38. The arm 38 may be given a partial rotation to vary the inclination of the tools by means of a worm 40 engaging a toothed segment thereon. The worm 40 is rotated by means of a hand wheel 41 or by a reversing worm, cams, connecting rod and crank or other automatic means driven from the lathe spindle. The pitch of the tools in the disc 11 must be a multiple of the pitch of the worm or equal thereto and must divide exactly into a circle of radius R. The gear wheels 32 .. 35 may be recessed into the disc 11, the cover plate 31 or into both and the intermediate wheels 33 may be mounted on adjustable centres in order to take up backlash between the teeth. In each construction in the slide 10 moves in a bracket 23, Fig. 1, vertically adjustable on the bed 24 of the lathe by means of slots and bolts 24<1> and is fed radially with respect to the work by a hand wheel 25, and a screw or automatically by a screw 48, Fig. 4, rotated by a worm drive 45 from the lathe spindle. The depth of cut is limited by a rod 50 adjustably secured to the slide 10 and carrying a striker 51 adapted to engage a lever 52 having a detent 53 which, when released from a shoulder 54 on the bracket carrying the worm 45, allows the latter to drop out of engagement with its wheel. Oil may be supplied to the gears 32 &c. through a central passage 44 in the shaft 36. The Provisional Specification states that when one tool only is used the work may be moved to maintain the cutting edge of the tool at right angles to the helix and refers to Specification 223,963, [Class 80 (iii), Linkwork &c.].