884,801. Centreless grinding. SHEFFIELD CORPORATION. Dec. 16, 1959 [Jan. 2, 1959], No. 42841/59. Class 60. [Also in Group XIX] In a centreless grinding machine means are provided for simultaneously supporting a pair of workpieces, each in contact with the regulating and grinding wheels at different fixed positions along the wheel peripheries for simultaneously grinding both workpieces. In the application of the invention to a machine for grinding mushroom-headed valves in pairs, the valves 34 are symmetrically positioned above and below a line between the centres of a grinding wheel 15, Figs. 4 and 5, and the regulating wheel 42, but a plurality of grinding stations may be provided with one on the line between centres or otherwise spaced to provide for the "unequal" grinding of workpieces of different diameters, or by a sequence of stations to effect rough and finish grinding of the same workpiece. Alternatively, the invention may be applied to the grinding of a workpiece comprising a plurality of separate parts, such as inner ball races, mounted together on an arbor, Fig. 12 (not shown). The grinding wheel 15, having axially-spaced portions 30, 31, Fig. 4, is carried by a slide 14, Fig. 1, operated by a cam 20 and roller 22. A workpiece-handling unit 12, Figs. 1 and 5, cooperates with an escapement device 35 which feeds pairs of valves 34 into recesses 37 in the periphery of a feeding wheel 40 concentrically rotatable in relation to the continuously-driven regulating wheel 42. A double acting air-cylinder 70, Fig. 1, is sequentially operated to effect the release of pairs of valves stacked in the device 35 via shoots 45, 46, to the feed wheel 40 which is supported by bearings 90, 92 on a shaft 81, to which the regulating wheel 42 is keyed for driving by a motor and belt-driven pulley 89. Intermittent feeding motion is effected by a motor 100, Fig. 4, a combined clutch and brake unit 101, and an index unit 102 which drives the feed wheel; a cam 110 engages a follower 111 after one complete rotation of the input shaft to engage the brake through an electrical circuit and to release the clutch after the desired rotation of the feed wheel 40, thus moving pairs of workpieces from loading to grinding and unloading positions by increments of 45 degrees. The valves 34, loosely positioned by the wheel 40, are precisely located and supported during grinding by an arm 120, Fig. 5, which is pivotally supported at 121 and is cam-operated at its lower end to swing counterclockwise, from the position shown, to clear the workpieces in readiness for further feeding. Pairs of blocking rolls 125, 127, carried by the arm 120 yieldingly engage the lower and upper workpieces of each pair during grinding and a positioning assembly 170, Fig. 4, is provided at each grinding location, comprising a spring-loaded positioner 172 mounted in a carriage 175 and a follower 180 in engagement with a circular cam-track 184 on the adjacent face of the feed wheel 40 whereby, during indexing, the carriage and positioner 172 are retracted; the valve stem end is located during grinding by an adjustable stop 165. Rollers or other friction-reducing means may be employed between the end of the positioner and the valvehead. The valves are supported within the recesses 37 by a retaining bar 190, Fig. 5, which terminates at a discharge shoot 115, Fig. 17 shows a modification in which the grinding wheel has an extension 271 beyond the plane of the regulating and feed wheels for grinding the valve head, a pair of rolls 274, spring-urged towards each other, serving as supports for the head. These rolls are carried by a structure 280 which is itself pivotally mounted on the base 10, as in the case of the arm 120. Fig. 10 shows diagrammatically the electropneumatic controls for operating, in timed sequence, the stacked valve (or other workpiece) escapement device 35, actuated by the cylinder 70, and an actuator 155 for moving the cam-face controlling the movements of the clamping arm 120. The cycle begins when the cam 20, Fig. 1, feeds the wheel-head slide 14 into grinding position. After completion, the limit switch 27 is closed and, acting through control circuits within a cabinet 220, energises a valve-actuating solenoid 217 to effect withdrawal of the arm 120 from the workpieces. On completion of this movement, a limit switch 160 is closed to effect engagement of the index unit clutch and to release the brake until switch 112, Fig. 4, is actuated to reverse this operation and to operate a second valve-actuating solenoid 218, permitting return of the actuator 155 and the clamping arm 120 towards the workpieces and closing a limit switch 159 which controls the drive of the cam 20 and also effects the operation of a solenoid 204 to open a valve 200 of the actuator 70 which is moved to release a further pair of workpieces from the device 35. A limit-switch 74 serves as an interlock by operating a solenoid 205 which returns the device 35 to its locked position; if workpieces are not released to the feed wheel 40 a new grinding cycle will not begin. In the modification shown in Figs. 14 and 15, a gauging station 240 is located below the feed wheel 40. Each work-holding recess 37 in the wheel periphery has an additional opening 246 to accommodate a pair of gauging calipers 247 and 248 carried on a common support 249 and actuated when the wheel 42 is at rest by a pneumatic cylinder 250. Air leakage orifices 252, 254, Fig. 15, connect with supply pipes 257, 258, each of which may be connected to a conventional indicating device or to switch contacts 260, 262.