623,395. Trueing and forming grinding wheels. PICKERSGILL, L., and WORLD MOULDED METAL CO., Ltd. June 3, 1946, No. 16740. [Class 60] In apparatus for trueing or forming a grinding wheel of the kind in which the motion of a diamond or other cutting tool is controlled by a tracing member through the medium of a pantograph mechanism, means is provided for securing a template or guide for the tracing member in opposed and reversed positions to enable positive and negative profiles which are complementary or have a uniform separation distance when suitably positioned to be formed using the same template or guide. In one form, Figs. 1, 2 and 2a, the apparatus is mounted on a baseplate 1 suitable for positioning on the magnetic table of a surface grinding machine, and the cutting tool 3 is adjustably mounted on an arm 5 secured to a spindle 6 mounted by ball bearings in a box member 11 pivoted to a second box member 30 forming a pantograph linkage. The member 11, which carries a curved transparent screen 15, is rotatably mounted by a ball race 19 on a plate 20 slidable by means of two rows of ball bearings 22 on a second plate 21 slidable at right angles by means of two rows of ball bearings 24 on a plate 23 secured to the base plate. A spindle 26 rotatable in the plate 23 carries an eccentric 27 engaging a ball race 28 in the member 11. The pivotal connection of the members 11, 30 comprises a double conical member 31 secured to the underside of the member 30 and carrying a crank 41 coupled by a bar 43 to the spindle 26. A spindle 37 journalled in the member 31 carries at its lower end a sprocket 38 connected by a chain 39 to a sprocket 14 on the spindle 6, and at its upper end a sprocket 44 connected by a chain 50 to a sprocket 49 on a tracing head spindle 45 mounted in ball bearings at the end of the member 30. This spindle carries a handle 52 fitted with an indicator plate 53 of V form and is formed with longitudinal diametrically-opposed slots in which slide locking members 55, 56 urged upwardly by a spring 57 and having outwardly directed lugs engaging slots in the bearing housing 54 carrying a housing 59 of inverted channel shape for a slide bar 60 adjustable by a clamp 61. The locking members are normally held down by a handle 58 which may be turned to allow them to rise and free the spindle from the housing 54. The lower face of the bar 60 is formed with a series of apertures for receiving a sleeve 67 housing the tracing pin 68 and having a head with an inclined face engaged by one of a number of inclined faces 63 formed on a locking bar 62 adjustable in the bar 60 by means of a clamp 64. The setting of the bar 60 is effected by gauge or distance pieces inserted between a block 65 on the end of the bar and the end of the housing 59. The pin 68 carries a ball 69 running on a table 70 to which a template 72 may be secured by screws 71 in reversed positions on either side. Tracing is effected by a removable collar 78 formed with a groove engaged by guide plates 80 of V form, see Fig. 4 (not shown), secured to the slide bar structure. For direct tracing from a template, the housing 67 is adjusted by sliding the bar 60 until the periphery of the collar 78 is aligned with the axis of the spindle 45. The amount of offset of the axis of the tracing pin is arranged to be a multiple of the radius of the edge of the cutting tool corresponding to the reduction ratio of the pantograph. As the handle 52 is operated to guide the collar over the template, it is maintained as far as possible normal to the curve of the template, and care is taken that the edges of the plates 53, 80 do not overlap the template 50 so that the tool does not foul the formed profile. Pure rotation of the spindle 45 is transmitted by the chain and sprocket connection, and displacement of the spindle effects relative angular movement of the members 11, 30 to operate the eccentric 27 and effect displacement of the spindle 6. Grinding wheel profiles which are spaced a uniform perpendicular distance from a profile corresponding to that of the template may be formed by offsetting the tracing pin by means of the bar 60. To form complementary profiles on two grinding wheels, or positive and negative profiles which will be spaced a uniform perpendicular distance when suitably positioned, a template is used having a profile spaced a uniform perpendicular distance from a profile corresponding to that to be formed, the amount of spacing being preferably a multiple of the radius of the cutting tip. The axis of the tracing pin 68 is aligned with that of the spindle 45, and the necessary offsetting of the pin is obtained by the use of collars of different sizes, see Figs. 7 and 8 (not shown). For tracing circular arcs without the use of a template, a plate 83, Fig. 6, carrying a rotatable spindle 86, is bolted to the plate 70, and the inclined head of the spindle is clamped in the bar 60 in place of the tracing pin. In a modification, Fig. 11 (not shown), two control handles are provided on the tracing head to effect displacement and rotation of the tracing head spindle respectively.