Patent GB-921600-A (GB)
Title: Method and apparatus for removing material from oppositely disposed surfaces
IPC: F16D3/224
Filed: 1961-12-29
Abstract: 921,600. Grinding-machines. MICHIGAN TOOL CO. Dec. 29, 1961 [Jan. 24, 1961], No. 46773/61. Class 60. A method of grinding oppositely disposed surfaces comprises the rotation of a tool between the surfaces, which are engaged by it successively, the tool passing along each surface alternately, and decreasing the distance from the tool axis to the surfaces at each pass, the amount of decrease being the same for each surface. As applied to grinding the concave arcuate grooves 16, Fig. 4, of a portion 13 of a universal joint, the grinding wheel 22 is rotated about an axis at right angles to the grooves, the axis itself describing circles of increasing diameter about a central point 23, Fig. 5, which is coincident with the axis XX of the shaft of the workpiece 11 and with the common centre of curvature of the grooves 16. A movement of the wheel axis from the centre 23 to the left along the line 21 takes place each time the wheel axis reaches the relieved portion 18, Fig. 4, on a line 28 so that as the wheel periphery approaches the upper surface an increment of feed is applied, the wheel axis continuing its orbit at this radius through the lower face until, at line 23, a further increment of feed is applied, the cycle being repeated until the required depth of groove has been ground or the tool is to be changed for a finishing cut, when the wheel axis is centralized between the upper and lower faces of the work and withdrawn therefrom along the line 21. After the completion of one pair of opposed grooves the work, which is held in a chuck, is indexed to bring it into position for grinding the next pair. The grinding wheel housing 53 is mounted on a slide 44 carried by a bed 45 which, at its opposite end 61, is supported by rollers 62 on the machine base 39; an arm 64 extends from the side of the slide 44 and is pivotally attached at its forward end 65 to a member 89, Fig. 8, forming the crank-pin of an adjustable-throw " crank " 82; the axis 68 of the crank-pin is coaxial with that of the grinding wheel spindle 41, when the wheel is in its forward or working position, so that the wheel axis follows the same orbital path as the crank-pin and thus the depth of cut may be adjusted by altering the throw of the " crank 82. This is effected by the mechanism shown in Fig. 8 in which the Z- shaped end 93 of an axially adjustable bar 92 engages rollers 85, 86 carried by the " crank " 82, whereby the throw may be varied by sliding it radially in dovetailed guides 83 across the face of the flanged end 81 of a hollow shaft 71 driven through worm gearing 74 by an hydraulic motor 75. The grinding wheel 'spindle 14 is also driven by an hydraulic motor 49 through belts 51, Figs. 6 and 14, the motor being adjustably mounted on the slide 44. The driving and grinding head assembly is retractable with the slide by a piston 48 to a position in which the periphery of the wheel may be dressed by a tool carried by a swinging arm on a bracket 56 and having provision for vertical adjustment by a cylinder 58. The axial adjustment of the feed-controlling bar 92 is effected by the mechanism shown in Figs. 11 and 12. A nut 99 is rotatable by ratchet means 101 in a housing 97 to shift a screwed shaft 109 coaxial with the bar and attached thereto by a coupling member 111. The housing 97 is also slidable in the same sense, on a portion 98 of the machine bed, by means of a vertically slidable member 115 having an inclined projecting rib 118 which is contacted by rollers 116, 117 carried by the housing; movements of the member 115 are effected by an hydraulic cylinder 121. The shaft 109 is also adjustable by a hand wheel 122 to reduce the orbiting radius when changing grinding wheels. Normal feed movements are effected by the slide 115 controlled by the cylinder 121, each increment being determined by a metering cylinder 144, Fig. 18, having a floating piston 145 and an adjustable stop 146 for controlling the stroke. A switch-operating cam 138, Fig. 4, rotatable with the shaft 71, and therefore with the orbiting movement of the grinding wheel, actuates switches LS1 and LS2 to control the operation of a feed relay which, through a solenoid 139, shifts a valve 141, Fig. 18, to regulate the flow to and from the cylinder 144 as the grinding wheel axis crosses the line 28, Fig. 4. Switches LS3, LS4 similarly actuate a valve 142 which controls the movements of the slide 115 in its limiting positions; thus the valve 141 controls feed increments and the valve 142 the re-setting of the piston-rod 119, thereby retracting the bar 92. A mechanical stop is provided to limit the increase in orbital radius so that several orbits at maximum radius may be made for finishing the grooves. The dressing means 55 is co-ordinated with other operations by limit switches (not shown) for reversing the oscillatory movements of the dressing head 57 at the end of each stroke and for simultaneous compensating movement of the ratchet 101 by a cylinder 106, Fig. 12, to increase the orbital radius, the wheel axis during the dressing operation being on the line 21, Fig. 5; a counter may be provided whereby the dressing head 57 is retracted by the cylinder 58 after a predetermined number of oscillations. A safety switch may be provided for controlling the advance of the slide 44 towards the workpiece after the dressing assembly is fully retracted.