573,877. Trueing grinding wheels. PORTER, C. B. A., SEYMOUR, C. P., and PRODUCTION PLANNING & DESIGN, Ltd. Dec. 21, 1943, No. 21423. [Class 60] Apparatus for dressing the working face of a grinding-wheel to a predetermined profile comprises a dressing-tool operated by pantograph mechanism having a member adapted to follow a template the dressing-tool being rockable about an axis including the point of the tool and tangential to the grinding-wheel, and the template follower being rockable about an axis perpendicular to the plane of the template in unison with the rocking of the tool ; the follower is moved bodily by a control member, rotation of which also serves to rock the tool and the follower. In Fig. 1, which shows a diagrammatic form of the apparatus, a base-plate 20 mounted on the magnetic or other chuck 21 of the grinding-machine carries, by means of a bracket 23, a board 25 to which is fixed, with its plane parallel to the axis of the grinding-wheel 38, a template 25 located by a straight edge 26 and stop 27. The pantograph linkage comprises a long link 28 pivoted at 29 to the base, a short link 30 also pivoted at 29, a lever 31 parallel to link 30 and pivoted to the free end of link 28, and a lever 32 parallel to link 28 pivotally connected between the upper end of link 30 and a point on lever 31. The lever 32 carries the dressing tool 34 near the link 30 and the lever 31 carries a pin 33 forming the template follower. The dressing- tool, which has a diamond point, is carried by one arm of an angle bracket 36 pivoted by a pin 37 in the lever 32, so tha,t the tool 34 can be set below the wheel 38 with the centre of its radiused point on the axis 39 of the pin 37 ; the radius of the follower pin 33 is equal to the radius of the diamond multiplied by the mechanical advantage of the pantograph. The pin 33 and the pin 37 are connected to rock in unison under control of a hand wheel 40 on the pin 33, by means of cranks 41, 42, links 43, 44 and a bell-crank lever 45. In operation, the follower pin is moved by the wheel 40 to follow the edge of the template, the follower and diamond being adjusted as necessary by the wheel 40 to enable them to trace all parts of the profile, for example, both flanks of the flange 47 ; a sector 35 attached to pin 33 and having an apex angle slightly greater than that of the diamond prevents the shoulder of the dressing tool from being cut by a part of the grinding-wheel. The apparatus, as used in practice, corresponds to the diagrammatic arrangement, and has conical spigot and socket bearings for the pantograph linkage and preloaded antifriction bearings for the dressing tool holder ; the pantograph also may include two opposite sides of channel-section bars nested together. The lever 32A is of channel section, and link 28A also is of channel section; and the bearings, shown in Fig. 5, include coneheaded pins 54, 55 in the base 20A engaging pins 58, 59 slidably mounted in the sides of the link 28A, the pins 58, 59 engaging a pin 60 secured in the link 30A, the various bearings being tightened by a screw and locked by clamping-screws. The link 30A is connected to the lever 32A by conical-ended pins 62, 63 engaging a pin 64 in link 30A and being loaded by a screw 65 ; the lever 31A is connected to link 28A and lever 32A by bearings similar to that last described. The bearing pin 37A of the dressing tool holder is mounted in the lever by pre-loaded ball bearings 70, 72, Fig. 7, the loading being effected by a nut 77, and the angle bracket 36A, integral with pin 37A, terminates in a block 81 carrying side plates 82 between which is slidable a block 83 with a V-notch 84 adjustable by a screw 87 to grip the shank of the dressing tool 34A against the block 81. The tool is adjusted for height by a screw 88<1>, and a gauge located by the upper face of the block 81, which is parallel to and at a known distance d from the axis 39A of pin 37A; alternatively, a machined face on lever 32A and a dial gauge may be used. The template follower comprises a hollow shaft carrying the pin and a hand wheel, the shaft being mounted by pre-loaded ball bearings in a head at the upper end of lever 31A; the sector is secured to the shaft by a screw. The lever 31A operates between guide rails carried by brackets on the template board and most of the weight of the mechanism is taken by a bell-crank lever 94 pivoted on link 28A and acted on by a spring 96 so as to ride on a block 98 on the base 20A. The bell-crank lever 45A is carried by the end of a bush.641 and movement is transmitted from the hand wheel 40 to the dressing tool by links 43A, 44A. In a modification, as applied to centre grinding- machines, the frame has a portion adapted to be mounted between the machine centres and carrying the template- and the linkages; the operation is similar to that described above. In the formation of grinding-wheels for grinding work profiles for example, as shown in Fig. 12, two templates are used to form two grinding-wheels with different profiles, these being used in succession so as jointly to grind the work to the required shape. In order to ensure that the finishing cut of the dressing- tool is made properly, an electric signalling device may be provided, comprising, Fig. 1, a lamp 107 and a source of current 108 ; when the follower pin 33 contacts the template, the lamp circuit is closed. The dressing-tool holder may carry two spaced tools, for roughing and finishing respectively.