Patent GB-920436-A (GB)
Title: An improved machine for grinding elongate workpieces
Inventor: PLUMMER HENRY JAMES
IPC: B24B17/00
Filed: 1959-05-01
Abstract: 920,436. Grinding and polishing. BRISTOL SIDDELEY ENGINES Ltd. July 29, 1960 [May 1, 1959], No. 14882/60. Class 60. A machine for grinding or polishing elongate workpieces having curved surfaces, such as compressor or turbine blades, comprises a stationary table having supporting positions for a workpiece and a former, a carriage supporting a rotatably-driven grinding head and a follower, arranged to engage the upper surface of the workpiece and the former respectively, the carriage being mounted on a cross-slide, arranged to be fed in steps transversely of the workpiece and the former, transverse guideways for the cross-slide being mounted on a slide, arranged for reciprocation longitudinally of the workpiece and the former, the carriage also being mounted for pivoting about a substantially horizontal axis, whereby the curved surface of the workpiece can be ground in accordance with the contour of the former. General.-A machine comprises a box base 1 having a top forming a slotted stationary table 2 on which a former and a workpiece can be mounted beneath a follower 3 and a grinding head 4. That part of the table 2 on which the workpiece is located is surrounded by a wall 6 forming a sink in which liquid coolant can be collected. The follower 3 and grinding head 4 are supported on a carriage 7 pivotally mounted, for swinging movement upwardly and downwardly about an axis 16 extending longitudinally of the machine, on a shaft 114 a cross-slide 8 movable, in increments of cross-feed from front to back of the machine, on a longitudinal slide 10 guided, for reciprocation longitudinally of the machine, on guideways 11. Grinding head.-The grinding head 4 comprises a casing 15 attached at the right-hand end of the carriage 7 and mounted on the shaft 114. An endless abrasive band 18 passes round a roller 5, idler rollers 19, 20, 21, 22, 23 and a driving pulley 24 driven by a belt 25 from an electric motor 26 mounted on the carriage 7. The rollers 21, 23 have adjustable mounts so that the tension in the band 18 can be varied, the idler roller 21 being mounted on a pivoted lever 27 loaded by a spring 28. The lever 27 carries a contact 29 which actuates a trip switch 30 to stop the machine if the band 18 breaks. The motor 26 is positioned substantially above the pivoted axis 16. The casing 15 is closed by an end door 31. Louvres are provided to circulate cooling air inside the casing 15 by utilizing turbulence caused by the travelling band. Follower.-The follower is an interchangeable sphere 3 mounted on the end of a shaft 36 rotatable in a downwardly-extending shaft 38 mounted in a housing 39 forming part of a bracket 40 attached at the left-hand end of the carriage 7 and mounted on the shaft 114. The bracket 40 is longitudinally adjustable on the shaft 114 to vary the longitudinal distance between the follower and the grinding head. The shaft 38 is axially adjustable in the housing 39 by a screw 47. The angular position of the shaft 36 is adjustable relatively to the grinding head, so as to vary the depth of cut, by swinging the bracket 40 about the pivot axis 16. To effect this, a strut has a part 42 connected by a trunnion mounting 39a to the housing 39 and a part 41 connected to a bracket 43 carried on the shaft 114, a calibrated head 44 keyed to the part 41 turning a screwed end thereof through a spherical nut 45 carried on the bracket 43. The part 41 carries a stop 46 which can be set so as to locate correctly the centre of the follower sphere 3 with respect to that of the roller 5 of the grinding head. Cross-feed mechanism.-The cross-slide 8 is fed by means of a shaft 50 which drives a shaft 67 through bevel gears 53, 54, shaft 52, universal joint 58, shaft 56, universal joint 59, shaft 57, bevel gears 62, 63, shaft 61 and bevel gears 65, 66. The shaft 50 is mounted in a housing 51 mounted just behind the front face of the base 1; the shaft 52 is mounted in a housing 55 supported by the housing 51; the shaft 57 is mounted in a housing 60 mounted at the rear right-hand end of the machine; the shaft 61 is mounted in a two-part housing 64 attached to the housing 60 and supported by the base 1. The shaft 67 extends longitudinally at the back of the machine and passes through a sleeve 70 supported by a bracket 71 extending rearwardly from the longitudinal slide 10, the sleeve 70 having an inwardly extending key 73 engaging a longitudinal key-way 68 in the shaft 67. The sleeve 70 is connected through bevel gears 75, 76 to the cross-feed lead screw 77. The shaft 50 can be rotated manually by a hand wheel 80 mounted on a sleeve 81 keyed to a shaft 82 having a spade end 83 engageable with a diametrical slot 84 in the front end of the shaft 50. To effect engagement and disengagement, the shaft 82 is axially movable by a knob 85, spring-loaded balls 86 engaging in alternative grooves 87, 88 in the sleeve 81. The shaft 50 can also be rotated automatically by an hydraulically operated piston 92 in a cylinder 90. The piston-rod 91 is connected to a rack 93 engaging a pinion 94 surrounding a sleeve 95 positioned around the shaft 50 and connected thereto by teeth 96. Between the pinion 94 and the sleeve 95 is a freewheel comprising balls 97 each positioned in a circumferentially-tapering slot 98 in the interior surface of the pinion 94. Movement of the piston 92 to the right rotates the shaft 50, but movement to the left does not. The amount of the automatic feeding increment of the cross-slide is controlled by a cam 100, adjustable by a handle 101, which limits movement of the piston-rod 91 to the right. The cross-feed cylinder 90 is actuated by a solenoid-operated switch (not shown) when the longitudinal slide 10 passes through its mid-stroke so that an increment of cross-feed is automatically applied. Longitudinal slide and cross-slide assembly.- The longitudinal slide 10 comprises a central part 105 having longitudinally extending front and rear guides 106, 107 supported on guideways 11 on the base 1, the guideways being protected by covers 108, 109 attached to the base 1. The central part 105 has a depending bracket 120 connected to the piston-rod of an hydraulic cylinder (not shown) for reciprocating the slide. The central part 105 supports two transverse V-rails 110 engaged by two V-rails 112 on the main body 111 of the cross-slide 8. The body 111 has bearings 113 for the shaft 114 which provides the pivot axis 16 for the follower bracket 40, the grinding head 4 and the carriage 7 which is connected between them and covers the body 111. An hydraulic cylinder 122 mounted on the cross-slide 8 contains a piston with a rod 122a connected to the top of the carriage 7 to swing the carriage 7 about the pivot axis 16 at the end of a machining operation. An upward extension 116 at the back of the body 111 supports a screwed sleeve 117 through which passes the cross-slide feed serew77. Taper attachment.-The limits of the longitudinal reciprocating movement are controlled by a taper attachment positioned in a shallow box 124 in the front of the base 1 and comprising a shaft 125 movable longitudinally of the machine. A rack formed on an intermediate part of the shaft 125 is engaged by a pinion 126 connected by a shaft 127 to a wheel 128 rotated by two steel tapes 129 connected to the bracket 120 underneath the longitudinal slide 110; the tapes pass round idler rollers 130. Thus, reciprocation of the slide 10 reciprocates the shaft 125; the diameter of the wheel 128 is twice the pitch circle diameter of the pinion 126, so that movement of the shaft 125 is half that of the slide. The shaft 125 carries longitudinally adjustable blocks 132 on which are mounted angularly adjustable end stops 133. At a central position in the front of the box 124 is a stationary tubular column 134 containing a screwed spindle 135 driven, through skew gears 136, 137 of equal diameter, by the shaft 52. The pitch of the screw of the spindle 135 is half that of the cross-feed lead screw 77. The spindle 135 engages a nut 138 vertically movable inside the column 134 and carrying a carriage 140. At the ends of the carriage 140 are limit switches 141 connected in the circuit controlling the hydraulic cylinder which reciprocates the longitudinal slide 10 and co-operating with the end stops 133 to effect reversal of the slide 10. As each increment of cross-feed is applied the spindle 135 is rotated so lowering the carriage 140 so that, according to the angles to which the end stops 133 have been set, the distance between the points on the end stops engaged by the limit switches is changed. A collar 143 is vertically movable on the column 134 by a knob 144 which turns a pinion 145 in the collar engaging a rack 146 on the outside of the column, the collar 143 carrying a trip switch 147 engageable by a stop 148 on the carriage 140 so as to stop the machine after a desired cross-feed has been applied. For machining blades which are tapered in the longitudinal direction, a sine-bar 150 is mounted on the blocks 132, its inclination to the shaft 125 being varied by altering the relative positions of the blocks 132. The carriage 140 carries a limit switch 151 arranged to engage the sine-bar 150 to reverse the longitudinal slide before the left-hand stop 133 is engaged by the limit switch 141. In a modification, an attachment is provided on the table 2 to support the workpiece and former in longitudinal alignment for angular movement about their longitudinal axes, an angular increment being applied to the workpiece and former each time a cross-feed increment is applied, to enable the follower to act successfully on steep surfaces such as encountered at the leading edge of a compressed or turbine blade. Specifications 793,366, 838,887 and 881,059 are referred to.