Patent GB-572605-A (GB)
Title: Improvements in or relating to apparatus for generating involutes
IPC: B23F5/02
Filed: 1943-07-20
Abstract: 572,605. Non-circular compasses. KAPELLA, Ltd., and COOKE, E. A. July 20, 1943, No. 11811. [Class 97 (iii)] [Also in Groups XXII and XXIII] In apparatus for generating involutes, a radius arm is pivotally movable about a main axis concentric with the base circle from which the involute is to be generated and carries a tangent arm which is tangential to the base circle, a follower being slidable along the tangent arm, when the two arms are moved about the'main axis, through a distance equal to the are subtended on the base circle by the angular movement so that the follower describes the required involute. Adjustment of the radius arm relatively to the main axis causes the tangent arm to be tangential to base circles of different size and so enables different involutes to be generated. A machine embodying the apparatus may be used for finish grinding or milling gear-wheels, making cutting tools or gauges of involute form, trueing grinding discs of involute section by means of a diamond tool or for testing or marking out involute curves on work-pieces. The essential features of the mechanism are shown in Fig. 3, wherein a disc or drum A is held stationary and defines the main axis A<1>. A flexible band B is secured to the drum A and has its free ends attached to slides B<3> movable in guides B<4> in a link D<2> mounted to pivot about the axis A<1>. As the link D<2> is moved round the axis A<1>, the slides B<3> move in opposite directions relatively thereto and act through rollers B<5> thereon on a lever E<3> pivoted to the link D<2> at D<1> to oscillate the lever about its pivot. An arm E<4> is attached to the lever to oscillate therewith and has a slot engaging a three-point roller unit E<5> on a slide F<1> movable in guides F<2> forming the tangent arm which is integrally attached to the radius arm F adjustable on a guide A<2> on the link D<2> radially with respect to the axis A<1>. A follower B<2> on the slide F<1> thus traces out the required involute when the link D<2> is moved round the axis A<1>. The mechanism may form an attachment to a copying machine of the kind described in Specifications 481,591, 499,751 and 538,726, [all in Group XXII], or in Specification 570,189, in which a base A, Fig. 5, carries rollers A<2> for guiding a longitudinal carriage B on which a transverse table C is adjustable by similar roller guides A<2>. Adjustment is effected by hand wheels B<5>, C<6> respectively and feed screws and is indicated by scales B<1>, C<1> on transparent windows on the slides co-operating with stationary indexes and illuminated from below. The table C has bearings for three vertical rotary spindles arranged at the apexes of an equilateral triangle and interconnected by a gear-wheel I, Fig. 6, one spindle carrying a work table E, another a pattern table H<8> and the third carrying a drum Q<2>, Fig. 21, corresponding to the drum A of Fig. 3. A grinding or milling cutter K is normally stationary and is adjustably mounted at K<4> on the machine frame A and a bracket L <1> fixed on the frame carries a microscope L for viewing the operative edge of the cutter and the part of the work being operated upon. Another fixed bracket L<3> carries a projection objective L<2> for throwing an image of a pattern &c. on the table H<8> on to a vertical screen L<4>, measuring scales as described in Specifications 572,144 and 570,189 being provided beneath the table for projection on the screen so as to be superimposed on the images of the pattern, the measuring grid, a profile of the tool &c. Flexible bands Q<7> are attached to the drum and also to slides Q<6> movable in guides on a link Q<4> which is rotatable in a bearing inside the drum. Rollers R<2> on the slides Q<6> engage opposite ends of a lever R pivoted at d<1> on the link Q<4>. A guide Q‹ on the link supports an L-shaped jockey Q<10>, Q<11> adjustable on the guide by a screw and handle Q<12> and a follower plate R<4> is slidable along the arm Q" of the jockey and carries a bogie R<6> having rollers R' making a threepoint contact with a guide R<8> on the lever R. To generate an involute on a work-piece mounted on the table E, e.g. a gear-wheel W, Fig. 36, the machine is set in zero position in which the axis of the table E is directly on the axis of the microscope L, the axis of the pattern table H<8> and projector L<2> are also coincident, the radius arm Q<10> of the jockey is perpendicular to the line joining the axis of table E and drum Q<2> and the axis b<2> of a socket R<5> on the follower R<4> is coaxial with the drum. The drum Q<2> is locked to the table C and the table locked against movement, a spigot S on a linkage S<9> pivoted to the machine is attached to the socket R <5>, the link Q<4> is locked against rotation by a stop R<9>, and the jockey Q<10> is adjusted laterally by the handle 12 until the socket axis b<2> is displaced from the main axis a<1> by a distance R equal to the radius of the base circle from which the involute is to be generated. This adjustment may be effected by the use of a gauge pack V'‹ and an electromagnetic gauge V as described in Specification 570,493, [Group XIX]. The joints of the linkage S<9> are then locked so that the axis of the socket R<5> becomes a fixed point relatively to the frame of the machine. The table C is adjusted longitudinally through a distance r equal to the radius of. the circular edge of the cutter K, using the measuring scales and screen L<4> as described in Specification 572,144, thus moving the follower R<4> along the tangent arm Q<11> by this amount. The linkage S<9> is ,then released and the table C moved laterally through a distance (R-r) so as to bring the centre of curvature of the cutter on to the base circle of the gear-wheel W, and the linkage S<9> re-clamped, the parts then being in the positions shown in Fig. 36. The gear is adjusted about the axis of table E so that the flank of a tooth overlaps the axis of the microscope L by the amount to be ground off the flank, the carriage B and table C are released for free movement, the stop R‹ is removed and the link Q<4> is oscillated about the axis a', thus causing the work to describe an involute path relatively to the stationary cutter K. Involutes from different base circles are obtained by adjusting the jockey Q<10> laterally on the link Q<4>. For generating a concave involute on a cutter W<1>, Fig. 39, the adjustments are as described above except that the table C is adjusted laterally through a distance (R+r) and the link Q4 is then oscillated about the axis a<1> in the opposite direction to the previous one. In grinding gear teeth by a cutter having a bevelled or chisel edge instead of a circular edge, the adjustments are the same as above except that the table C is moved through a distance R and the follower R<2> is not adjusted along the arm Q<11>, the operative edge of the cutter then being located on the base circle of the involute to be generated. To generate an involute tooth by means of a grinding disc having a rack tooth section, the jockey Q<10> is adjusted relatively to the axis a<1> through a distance equal to the pitch circle radius, the spigot S is inserted in the socket R <5> and the linkage S<9> locked, the table C is adjusted laterally through this distance r, Fig. 36, thus positioning the cutter with its operative edge on the base circle. The clamp R<9> is then released to allow rotation of the link Q<4> and the drum Q<2> is rotated by a worm and hand wheel J<8> causing the table C to be traversed past the cutter and the work to be rolled along its theoretical pitch line. 'For producing a concave involute surface on a grinding wheel, the jockey is displaced from the axis a<1> by the radius r, Fig. 44, of the pitch circle, the spigot S inserted and the linkage S' locked, the table C is moved longitudinally through a distance y equal to half the grinding wheel thickness and transversely through the distance r, 'and the link Q<4> is oscillated to swing the wheel K past a diamond K<15> whose point is located on the axis a<1>. For grinding a convex involute on the wheel K, the jockey is set a distance r on the other side of the axis a<1>. In a modified machine for checking involute curves, a base A<16>, Fig. 45, carries the drum Q<2> connected by the tape and lever mechanism to the follower R4, and a work table H<16> is rigidly attached to the base. A bracket Q<17> is mounted on the follower R<4> and carries a projection objective L<16> coaxial with the socket axis of the follower R<4> and a screen L<17> on which an image of the work to be tested is projected, pivotal movement of the link Q<4> about its main axis causing a datum on the screen to move in the required involute path which may be compared with the work image on the screen. Alternatively, the follower R4 may actuate a feeler or lever mounted on a spring ligament support and operatively connected to a mechanical or electrically controlled indicating or recording instrument, or a stylus or other marking device may be substituted for the cutter so as to mark involutes on work-pieces mounted on the work table. The machine shown in Figs. 5 and 6 may be used for generating arcs of circles in the same manner as is described in Specification 570,494, [Group XXII], the jockey Q<10>, Q<11> replacing the block H described in that Specification, and the involute generating mechanism may be attached to the shafts of the work table E or the pattern table H<8>. The Provisional Specification states that mechanical gearing may replace the tapes Q<7>.