Patent GB-869304-A (GB)
Title: Improvements relating to machines for grinding toothed parts
IPC: B23F23/00
Filed: 1958-08-28
Abstract: 869,304. Grinding. GLEASON WORKS. Aug. 28, 1958 [Sept. 6, 1957], No. 27689/58. Class 60. A tooth grinding machine comprises grinding wheel and a work spindle, means including a rotary feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a tooth surface of a workpiece, on the spindle and for returning for a subsequent infeed, and means for angularly indexing the work spindle between successive infeed motions, the infeed portion of said cam comprising a plurality of discrete infeed sections separated by retraction sections, so that while the infeed is occurring the wheel and the tooth surface being ground are periodically separated. The workpiece C, e.g. a face toothed clutch, is secured by chuck means to a work spindle 27 journalled, for rotation about a horizontal axis, in a work head 25 angularly adjustable, about a vertical axis, on a crossslide 23 adjustable horizontally on a slide 21 moveable along horizontal ways on the machine frame 20. The grinding wheel W is secured to a spindle 31 driven through pulley 34 and journalled in a quill 32 axially slidable in a carrier 33. The latter is pivoted by a pin 35 to a cradle 36, a worm 41 journalled in the cradle 36 meshing with a worm-wheel segment 42 on the carrier 33 for adjusting the carrier relative to the cradle. The cradle 36 is angularly adjustable through 360 degrees, about a horizontal axis, relative to a housing 38 rigid with the frame 20. The workindexing mechanism comprises a motor 43 driving, through worm gearing, a shaft 45 connected by an electromagnetic clutch 46 to a shaft 47 controlled by an electromagnetic brake 48. The motor runs continuously ; the clutch and brake may be energized alternately so that shaft 47 turns intermittently. On shaft 47 is a drive member 53 carrying roller 54 cooperating with slots 55<SP>1</SP>, 55<SP>11</SP> in a driven member 55 splined to a shaft 56. A gear segment 57 on shaft 56 is adapted to mesh intermittently with a pinion 58 on shaft 47. The driven member 55 is moved axially, through lever 59, by a cam 52 on a shaft 51 driven, through reduction gears 49, by the shaft 47. The driven member 55 drives the work spindle 27 through gears 62, 63, change gears 65 and worm gearing 67, 68. The change gears 65 are selected to give the desired angle of indexing. During the intervals between indexing the work spindle is held against rotation by a spring-backed lock dog engaging a notch in a plate 69 on shaft 64 ; the dog is disengaged from the notch prior to indexing by a cam 71 co-rotatable with cam 52. Alternate relative infeed and retraction of the grinding wheel and work spindle in time with the indexing are effected by a feed cam 72 driven, through worm gearing 76, by a variable-speed reversible motor 75. The cam acts against a follower roller 77 carried by a cylinder 78 slidable in a guide 79 of the frame ; the cylinder contains a piston 81 whose rod 82 acts, through a pin 83 slidable in a bushing 84 in the cradle 36, on a lever 85 pivoted at 86 to the cradle. The end of the lever is pivotally connected to a spool 88 slidable on pivot pin 35 and acted upon by a spring 89. The spool is connected to a cylinder 91 slidable in the carrier 33 ; a piston 94 in the cylinder has a rod 93 screw-threaded to a non-rotatable nut 95 carried by the quill 32. Normally hydraulic pressure acts on the left of piston 94 so that rod 93 abuts a stop button 96 when the high point of feed cam 72 engages follower roller 77. When the grinding wheel is to be dressed, piston 94 is moved to the left to retract the wheel, and the wheel is advanced slightly by rotation of rod 93. This rotation is effected, through gears 104, 103, 102 and bevel gear 99 by a ratchet operated by a piston 97 and cylinder 98. The piston 81 and cylinder 78 constitute a collapsible strut ; the opposite ends of the cylinder 78 are connected by conduits 106, 107 to the opposite ends of a cylinder 105 containing a piston 108 reciprocated by a cam 109 on shaft 51, the cam having an endless path so shaped that prior to indexing piston 108 is moved to the left to collapse the strut and at the conclusion of indexing to the right to extend the strut. For controlling the position of the slide 21 on the frame 20, the slide 21 is connected to piston rod 121 of a piston 119 in a cylinder forming part of a slide 118. The slide 118 is adjustable on the frame 20 by a screw 112 rotatable by bevel gearing 114 and a shaft 115 adapted to be turned by a socket wrench and carrying a calibrated dial 116. The slide 118 is secured in adjusted position by clamp screws. A shaft 123 rotatable in the slide 118 carries a position-indicating dial 124, a ratchet wheel 125 and a variable stop drum 126, the right face of the latter having circularly arranged relatively stepped stop surfaces 127, each step representing the amount of infeed of the work relative to the wheel between successive grinding passes during finish grinding. To limit advance movement, i.e. to the left, of the slide 21 effected by the piston 119 one of the stop surfaces 127 is abutted by one end of a bar 128 slidably supported by slide 118 and arranged to abut at its other end one of a series of circularly arranged, relatively stepped stop surfaces 129 on a disc 131. The disc 131 is secured on a shaft 132 rotatable, in a bracket 122 attached to slide 21, by a knob 133 held in adjusted position by spring-backed detent 134. When the slide 21 is withdrawn the bar 128 is moved clear of the stop surface 127 by a spring 136 acting on a pin 137 on the bar, movement being limited by abutment of the pin 137 against a step 138. The mechanism for automatically turning the ratchet wheel 125 and stop drum 126 comprises a piston 139 engaging a pin 141 carried by a rocker 142 angularly movable on the shaft 123 and a pawl 143 carried by the rocker and engaging the ratchet wheel. Upon each stroke of piston 139 to the right, the ratchet wheel is advanced by one tooth and the stop drum by one step. During the return stroke of the piston the stop drum assembly is held against retrogression by a friction brake 144. Upon completion of the finish grinding cycle the pawl 143 is released by motion to the' left of a piston 145 and the stop drum assembly is returned to its initial position by motion to the right of a piston 146 having rack teeth engaging gear teeth 147 on shaft 123. The initial position of the stop drum assembly is adjustable by means of a screw 148 limiting the stroke of piston 146. Thus any desired number of the steps provided on stop drum 126 may be utilized in finish grinding. The wheel W is periodically dressed by automatic dressers whose operation is controlled by a motor-operated control unit 149. The reversible variable speed motor 75 for feed cam 72 is controlled by four independently adjustable electromagnetic controllers for roughing feed, roughing return, finishing feed and finishing return. These controllers are governed by means including normally open limit switches 156, 157, 158. Switch 156 is closed by a cam 159 on shaft 73 only when the " O" (high or zero) position of cam 72 contacts follower 77. Switch 157 is closed by a stop 161 adjustable on the cam, being set at various angular distances from the "O" position depending upon the amount of roughing feed motion desired, the maximum setting being that in which stop 161 closes switch 157 when "R" position of the cam contacts follower 77. Switch 158 is closed by a stop 164 fixed to the cam this occuring when "F" position of the cam contacts the follower 77. The roughing feed path of the cam, from roughing start point "R" to high point "O" comprises discrete infeed sections 165 constituting spirals of gradually increasing radius separated by depressions 166 constituting retraction sections allowing a slight motion of the follower 77 and wheel W to the left under the urge of spring 89 sufficient to allow the entry of coolant between the wheel and the surfaces being ground. The finishing path "F" to "O" of the cam is a spiral of continuously increasing radius so that the wheel is fed quickly into full finishing depth without interruption. The control system includes two electrically operated counters which are actuated upon each closing of a switch 184. This switch is momentarily closed by a cam 185 on shaft 51, once upon each revolution of the latter. One counter is adjustable for a number of rough grinding cycles to precede each dressing operation. The other counter is adjustable for the total number of teeth in the workpiece. During rough grinding and also during the subsequent finish grinding, there is alternately an indexing of the work and an infeed of the grinding wheel by cam 72, the indexing occuring during return motion of the cam. While indexing is taking place the strut 78, 91 is in collapsed condition so that the grinding wheel is withdrawn clear of the work. Upon the return motion of the feed cam being completed before indexing is completed, the drive for the cam waits until the indexing has terminated before starting the next infeed. Similarly an indexing operation cannot commence until the preceding cam-effected infeed has been completed. Throughout rough grinding the slide 21 remains in the. same advanced position except for its periodic withdrawal for redressing of the grinding wheel. After the rough grinding has been concluded the variable stop 126 becomes active. That is, during the finish grinding phase, upon each withdrawal of the slide 21 occurring after the workpiece has been indexed completely around, i.e. through 360 degrees, the variable stop turns to allow the slide 21 to advance one step further, so that the subsequent grinding will be at greater depth. Thus during the rough grinding phase each tooth space is ground to full roughing depth by a continuous infeed of the grinding wheel before the work is indexed, and all of the teeth are roug