Patent GB-976647-A (GB)
Title: Centreless grinding machine
IPC: B24B47/04
Filed: 1961-12-08
Abstract: 976,647. Grinding. VAN NORMAN INDUSTRIES Inc. Dec. 8, 1961 [Dec. 8, 1960], No. 44086/61. Heading B3D. A centerless grinding machine has motor means which effect reciprocation of the regulating wheel assembly 32, Figs. 1 and 3, towards and away from the grinding wheel assembly 30 and include a driven shaft 208, Fig. 12, rotatably supported in the assembly 32 and a pitman 204 pivotally connected at one end to an eccentric portion 206 of this shaft and at the other end to an adjustably-located positioning means 196 defining an initial position of the assembly, each rotation of the shaft 208 resulting in reciprocation of the assembly from its initial position towards and away from the grinding wheel assembly. The invention is described in relation to a machine wherein workpieces are fed one at a time from a magazine 300, Fig. 26, to a workrest blade 298 on the regulating wheel assembly 32 which for each grinding action is given the reciprocating movement referred to above, such movement consisting of rapid advance towards the grinding wheel, slow feed for grinding and " sparking out " and rapid return. The machine also includes means under the control of the operator for giving both grinding wheel dressing mechanism enclosed in a casing 48, Fig. 1, and the regulating wheel assembly 32 a compensating advance towards the grinding wheel and setting the dressing mechanism into operation. The grinding wheel assembly 30, Fig. 1, in which the wheel G is rotated by a belt drive, is mounted directly on the bed 34, and the regulating wheel assembly 32 comprises a base 56, Figs. 3 and 4, which is reciprocated on the bed in the manner referred to above and a superstructure mounting the wheel R and a motor 40 for rotating it through a belt drive 116. The superstructure consists of a casting 60, Figs. 4 and 6, which is adjustable transversely to the direction of reciprocation of the base 56 by a hand-operated lead screw 70 and has mounted in a slideway in its side wall 64, for slidable adjustment in the same transverse direction by a further hand-operated screw 90, a plate 82 carrying a mounting plate 86 for the wheel R and motor 40. The screw 90 provides for adjustment of the wheel R to and from the face plate 66 of the casting 60 according to the length of the workpieces being ground, and the screw 78 provides for adjustment of the superstructure as a whole and may be associated with indicating means 94. To permit tilting adjustment of the regulating wheel R the plate 86 is arranged to be clamped to the plate 82 by bolts which allow for limited adjustment of the plate 86 as shown by a scale 158, Fig. 4. Reciprocation of the base 56 to and from the grinding wheel is effected by rotating the shaft 208, Figs. 3 and 12, through a belt drive from a D.C. motor, the pitman 204 embracing the eccentric portion 206 at one end and being pivoted at the other on a pin 196 on a block 192 slidable in the base 56. The initial position of the block and therefore of the base 56 is determined by a feed screw 186, Fig. 11, which is rotatable through gearing 176 ... 184 by a hand-operated shaft 170 and is in screw-threaded engagement with two nuts 198, 200, Fig. 12, in the block; the nut 200 is fixed in the block and so provides adjustment of the latter when the feed screw is rotated and the nut 198 is slidable in the block and spaced from the nut 198 by a compression spring 202 to take up back lash. The shaft 170 is also arranged to be operated automatically so as to give the regulating wheel assembly a compensating advance towards the grinding wheel by the compensating mechanism described below in connection with the grinding wheel dressing mechanism. The D.C. motor tracted position by an aajustaDle arm 304 which is rotatable and axially movable on a shaft 306 and carries at its free end a pintle 308 for engaging within a workpiece. The arm is swung between the magazine and blade by a link 326 connected to a crank arm 324 which is so driven through cam means from a shaft 314 driven in turn by the shaft 208 reciprocating the assembly 32 that, with the pintle 308 engaging the lowermost workpiece in the magazine, the arm is first swung down to position the workpiece on the blade under the guidance of a pivoted blade 302 while the assembly is in retracted position, then urged against a stop 312 while the grinding operation is being carried out, and finally returned to its vertical position by a spring 328. As the arm returns with the finished workpiece, it is caused to withdraw from the face plate 66 by the coaction of a cam 332 with cam means on that part of the arm surrounding the shaft 306 and so release the workpiece for discharge, with or without the aid of an ejector, to a shoot 348. Upon the arm reaching its vertical position, the coacting cam means permit return of the arm towards the face plate for the pintle to engage the next workpiece in the magazine. The cam 332 is arranged to be swung into inoperative position when the arm moves downwardly. If desired, this mechanism may be arranged to withdraw the pintle from the workpiece while the latter is being ground. The grinding wheel dressing assembly 48 is carried by a slide movable to and from the grinding wheel G and comprises three diamond tips on holders 252, Figs. 16 and 19, the central holder being carried on a rockable shaft 238 for dressing the rim of the wheel to arcuate form and the other holders being carried on respective arms 250 on shafts 246, 248 driven by gearing 240, 242, 244 from the shaft 238 for dressing the side edges of the wheel to a concave form. The shaft 238 is rotated from a reversible A.C. motor 220, Fig. 16, through a belt drive 222, gearing 226, 228 and further belt drive 234, a clutch associated with the gearing permitting hand operation when required. Upon 6 energization of the motor 220 for a dressing operation the diamond tip on the shaft 238 is rocked counterclockwise in Fig. 19 through 180 degrees and the tips on the arms 250 through 90 degrees, the automatic reversal of the motor then returning the tips to their initial positions at one side in readiness for the next dressing operation. The slide carrying the dressing aseembly can be advanced towards the grinding wheel by a feed screw 276, Fig. 24, actuated through gearing 270, 274 by a shaft 268 which is operable either by hand or, upon the initiation of a dressing operation, by compensating mechanism adapted to give both the dressing assembly 40 and regulating wheel assembly 32 an increment of advance towards the grinding wheel. The compensating mechanism comprises a reversible A.C. motor which when energized causes the rightward movement of a rack 286, Figs. 11 and 24, and the consequent rotation of the shafts 268, 170 for the advance of the two assemblies, the drive to these shafts being through gears 280, 174 and pawl-and-ratchet devices 278, 172 effecting drive only in the rightward travel of the rack. As the rack so advances, a dog actuates a switch both to reverse the motor so as to return the tack and energize the motor 220 in forward direction to rock the diamond tips through an operative stroke. The rack-driving motor is de-energized by the opening of a second switch by another dog and the motor 220 is reversed at the end of the operative stroke of the diamonds so as to return the latter to their initial positions. The grinding wheel motor, motor for driving the rack 286 and motors for driving the regulating wheel, shaft 208 and diamond tips are arranged for joint operation under the control of a circuit including appropriate start and stop switches, limit switches, relays and thermal overload-preventing devices for the respective motors. The control circuit for the motor driving the shaft 208 also includes a switch which can be set to either stop the motor after it has effected a single reciprocation of the regulating wheel assembly or provide for automatic repetitive reciprocation of the assembly. A dressing operation may be effected at the discretion of the operator by closing a switch which energizes the compensator motor in a direction to cause the rack 286 to advance the assemblies 32, 40 towards the grinding wheel; this motor will, however, only be energized provided the grinding wheel motor and motor reciprocating the regulating wheel assembly are energized since two switches in the control circuit of the former motor are automatically opened whenever these motors are not energized.