Patent GB-641593-A (GB)
Title: Improvements relating to a method of and apparatus for determining cam forms
IPC: G01B5/20
Filed: 1945-09-14
Abstract: 641,593. Copying lathes; making cams. POWER JETS (RESEARCH & DEVELOPMENT), Ltd., and KESTELL, T. A. Sept. 14, 1945, No. 23828. [Classes 83 (ii) and 83 (iii)] [Also in Group XXIII] The invention relates to obtaining the form of a three-dimensional cam for use in a profiling machine in which the work, such as a gas turbine blade, is rotatably mounted about a work axis and reciprocatory relative motion is effected between the work axis and a tool involving rocking of the work relative to the tool about a further axis, the extent of said rocking being varied by the movement of a cam follower over. the cam in accordance with a traversing movement of the work relative to the tool; apparatus for obtaining the form of the cam comprises the machine itself, and in the place of said cam and said cam follower, a link of adjustable length, of which one end is movable and is located at a position corresponding to the axis of said cam follower, while the other end is fixed at a position corresponding to the axis of said cam, a master pattern mounted on the work axis, means for mounting a dummy tool so as to be adjustable horizontally but rigid vertically, means for urging said dummy tool into contact with said pattern, means registering with said dummy tool for indicating the position in a direction perpendicular to the work-shaft, and means for measuring the movement of the movable end of the link. In a modification, instead of the machine itself, a mechanically equivalent linked framework is employed. The invention is described as applied to a profiling machine such as that described in Specification 641,591 comprising a rotating work-shaft 9 mounted eccentrically in a sleeve 10 rotatably mounted in a bore 2 in a profiling head 3, an arm 15 rigid with said sleeve 10 normally carrying a cam follower co-operating with a profiling cam normally mounted on a rotary shaft 17. In the present case, the arm 15 and shaft 17 are connected by a manually adjustable micrometer link 38 comprising a sleeve 22 with an eye 22A to embrace the shaft 17; the sleeve 22 has a threaded bore engaged by a threaded rod which is rotatable, by a handle 26, in a bush 49 secured, at a position corresponding to the axis of the cam follower, to a forked bracket 28 rigid with the arm 15. A linear scale is provided on the sleeve 22, and a circular scale in conjunction with the handle 26. The chuck or mandrel on the shaft 9 is replaced by a carrier 35 in which is mounted a master pattern 31 comprising a series of laminµ 33, each corresponding to a particular section along the blade and conforming to appropriate design curves, held in slots 39 in a holder 32, the space between the laminµ being filled in with a suitable material 34 to form a continuous profiled surface. The holder 32 is mounted in the carrier 35 by ballbearings 36 disposed out of axial alignment relative to the work-shaft 9 and an adjustably fixed abutment is provided for the base of the holder 32 so that the latter can be set up at any desired angle in relation to the work-shaft 9. A dummy grinding-wheel sector 12, Fig. 3, is supported by pivoted links 40 and a flexible metal strip 41 on a carriage 14; the strip 41 contacts the rod 42 of an indicator 13. The carriage 14 is mounted, by ball-bearings 58, on a slide 59 movable on a table 18. The carriage 14 is urged to the left by a spring 46; gauge blocks 37 are interposed between a datum stop 20 on the carriage 14 and the edge 43 of the slide 59. A projection 44 on the carriage 14 forms an abutment for a projection 45 on the sector 12 to prevent undue movement of the latter. A hand wheel 50 is mounted on the shaft 17 which also carries a wheel 51 having notches, at 5 degree intervals, engaged by a spring-pressed plunger carried by an arm 53 depending from the sleeve 22. In use, the dummy sector 12 is adjusted by movement of the slide 59 to contact a particular lamina 33 of the master pattern 31 which is then rotated through 5 degrees at a time, the micrometer link 38 being adjusted each time to maintain the indicator at its initial reading; the scales are read and noted. The operation is repeated for all the laminµ in turn. According to the Provisional Specification, a spherical milling cutter may be used in place of the cam follower so that the effective parts of the cam are milled direct, the run-outs being milled subsequently.