Patent GB-1487961-A (GB)
Title: Machine tools
IPC: B24B49/18
Filed: 1974-01-15
Abstract: 1487961 Grinding CENTRAX Ltd 13 Jan 1975 [15 Jan 1974] 01830/74 Heading B3D A machine tool comprises means for removing material from a workpiece supported by supporting means and movable along a predetermined path relative to the supporting means, and compensating means arranged to superimpose on the movement a compensating movement of the material-removing means relative to the supporting means at such a predetermined rate and in such a direction that the wear on the material-removing means is at least partly offset. As described, the machine tool is for polishing a turbine blade, which is mounted on a face plate 11 (Fig. 1) and a material-removing means is an abrasive belt 19. The face plate is rotatably mounted in a headstock 2 and driven by an hydraulic motor 7 which also drives a face plate 8 carrying a cam 9 corresponding to the shape of the turbine blade. The headstock is reciprocatable along guideways 3 by a piston- and-cylinder device 4, 5. The spindle carrying the face plate 11 also carries a cam 12 which co-operates with a follower 13 controlling a valve 14 which, in turn, controls the flow of fluid to motor 7 and the instantaneous rate of rotation of the face plates 8, 11. The abrasive belt 19 and a follower 17 for engaging the cam 9 are mounted on an assembly 16 pivoted about an axis 20 on a block 15 on the bed 1 of the machine by a pneumatic piston-and-cylinder device 21. The abrasive belt is guided over a pulley 23, Fig. 3, driven by an electric motor, idler pulleys 25, 27, 29 an idler pulley 26 acted upon by levers 32, 34 and a piston-and-cylinder assembly 35 to tension the belt, and a contact wheel 28. The contact wheel 28 is mounted on an arm 41 which is biased by an adjustable spring 42 about the pivotal axis 20 about which assembly 16 is moved by the device 21, the spring determining the pressure with which the contact wheel is pressed against the workpiece. The upper end of arm 41 engages one end of a lever 46 mounted on a vertical pivot 50, the other end of the lever co-operating with an adjustable stop and a microswitch to stop operation of the machine when the workpiece is to size. The follower 17 is in the form of a wheel which is mounted on an assembly 200 adjustable along slides 202 on the belt drive assembly 16 towards or away from the cam 9 to determine the size of the workpiece and to compensate for wear on the abrasive belt. The assembly 200 is clamped in its adjusted position by movement of a piston 208, Fig. 2, of a pneumatic cylinder 206, the piston having a wedge surface 212 which co-operates with a wedge surface 214 on a clamp bolt 216 passing through an elongated slot in the assembly 200. The assembly is movable along the slide 202, when the clamp is released, by compressed air acting first in the left hand side of a cylinder 224 having a piston 226, Fig. 6, secured to the casting 204 of the belt drive assembly 16, and then to the right hand side of the piston, the action also indexing the compensating means which limits the movement of the assembly 200 on the slide 202. The compensating means consists of a wedge 232 on a carrier 234, Figs. 5 and 6, urged in one direction along slides 236 of the casting 204 by a pneumatic piston-and-cylinder assembly 238, the wedge being engaged by an abutment 248 on the assembly 200 carrying the follower wheel 17. The abutment is adjustable by a knob 252 and has two surfaces for selective engagement with the wedge according to whether coarse or fine polishing is to be effected. The position of the wedge carrier is determined by engagement of one of a number of pins 240 arranged in two rows on the carrier with an abutment surface on the casting. As each reciprocation of the assembly 200, a trigger 244 fastened thereto acts to move the engaged pin into the carrier against the pressure of an associated spring so that the carrier is urged by the pressure in devcie 238 to engage the next pin 240 with the casting 204 whereby the assembly 200, and hence the follower 17, are advanced an micromental distance relative to the belt assembly 16 to compensate for wear of the belt 19. A belt crushing mechanism comprising a wheel 256, Fig. 3, which can be pressed by movement of a lever 258 upon actuation of a piston-and-cylinder device 262 against the idler wheel 25, the wheel having a waisted profile which co-operates with the crowning of the idler wheel 25 to flex and thus soften an initially flat newly-fitted belt 19.