778,479. Grinding gears; trueing grinding wheels. GLEASON WORKS. Aug. 19, 1955 [Sept. 7, 1954], No. 23957/55. Class 60 [Also in Group XXXVII] A gear-grinding machine comprises a conical grinding wheel W, Figs. 1 and 3, journalled for rotation in a head 45 which is movable rectilinearly on a support in the direction of a straight line lying in the conical surface of the wheel, a trueing device for the wheel mounted for rectilinear motion on the head in the direction of another straight line in the conical surface of the wheel and means for'effecting the two motions in pre-determined ratio; the trueing device is caused to move in its rectilinear path in response to the rectilinear movement of the wheel head on its support. this movement of the wheel head being that necessary to compensate for wear of the wheel. A cradle 31 mounted for oscillation about a horizontal axis 32 carries two conical grinding wheels W rotating about axes 33 inclined to and offset from the axis 32 for generating the tooth surfaces of a gear G rotatable by a motor 40 about an axis 37; the gear G is carried by a spindle journalled in a work-head 36 which is adjustable angularly about a vertical axis on a sliding base. Each wheel W is secured on a spindle 44, Fig. 3, journalled in a head 45 which has a cylindrical extension 51 slidable in ball bearings in the direction of the axis 32 on a slide 53; a motor 47 on the head drives the wheel through gearing 49. Each slide 53 is vertically adjustable by a screw on a plate 57 arranged to be similarly adiusted horizontally by a screw 63 on a plate 58 which is adjustable on the cradle 31 about the axis 32; a turnbuckle corrects the two plates 58 for simultaneous adjustment about the axis 32, and clamping bolts are, provided for securing all the parts in adjusted position. Feed of each wheel to compensate for wear is effected by a screw 54 which is mounted on the slide 53 in engagement with a nut- 55 on the extension 51 and carries at ratchet wheel 67 operated by a hydraulically-actuated piston 68, Fig. 5, having a pin-and-slot connection 73 with a pawl carrier 72 pivoted about the screw 54. The pawl 71 is actuated to advance the ratchet wheel 67 by the aid of a spring plunger 74 when the piston 68 moves outwardly and is withdrawn by a pin 75 on the return movement of the piston; the advance of the piston may be such as to advance the ratchet wheel for any number of teeth up to six as determined by the setting of a rotatable plate 78 having six differently-spaced stop faces for co-operation with a shoulder 77 on the piston. Rollers 81, Fig, 3, on the extension 51 co-operate with rails 82 on the slide 53 to prevent angular movement of the wheel head. The screw 54 may be held against unintentional rotation by brake shoes engaging a drum on the screw, and a hand wrench may be applied to a tubular shaft 88 for rotating the screw through gearing; a second hand wrench may be applied to a shaft 93 inside the shaft 88 so as to act through gearing and detent mechanism to set the stop plate 78 in desired position. Each wheel is provided with a dresser in the form of a diamond tool D, Figs. 8 and 12. controlled by a slide 105 movable on a frame member 102 on a bracket 80 fixed on the wheel head 45. The frame member 102 is adjustable on the bracket 80 in an arcuate track 80<SP>1</SP> centred about an axis 90 which is perpendicular to the wheel axis and tangential to the wheel periphery.. The slide 105 is secured on a rod 103 slidable axially in the frame 102 and guided by a second parallel rod 104, the two rods being parallel to the line w on the conical wheel surface in their zero position of adjustment. A cam follower 109 on the slide 105 engages a straight slot in a cam 111 on the slide 53 so that the former slide is given a feed movement in response to the wheel feed; this feed movement of the slide 105 is transmitted to the dresser housing 112 which is mounted for axial and pivotal motion on the rod 104 and is connected with the slide 105. The feed of the dresser slide is greater than that of the wheel to an extent which takes account of the fact that the depth of the arc of the concave tooth bottom in a gear ground by the wheel increases as the diameter of the wheel decreases, the ratio of the two feeds being varied for this purpose by adjusting the cam 111 about an axis which coincides with the axis of the roller 109 when the slide 105 is positioned for dressing a new wheel of regulation diameter and is perpendicular to the axis 32 and axes of the rods 103, 104. Further, since as the wheel decreases in diameter it is necessary that the surfaces 34, 100, Fig. 22, should recede to the positions 34<SP>1</SP>, 100<SP>1</SP>, the centre C of the round becoming progressively closer to the axis 32, the dresser slide is fed at the small angle A to the line w in the wheel cone surface as determined by the setting of the frame 102 about the axis 90. The diamond D is carried on an arm 116, Fig. 12, rotatable about the axis of a shaft 117 mounted in a bracket 113, Fig. 11 which has a tubular part 114 slidable along an. axis 115 in a bore in the dresser housing 112; the axis 115 is parallel to the common plane of the shafts 103, 104. but inclined to them at an angle equal to that between the plane side face 34, Fig. 22, and conical side face of the wheel W. The diamond trues the face 34 by movement of the bracket 113 along the axis 115, the round between the face 34 and tip 100 by swinging the arm 116 about the axis of the shaft 117, and the tip 100 by pivoting the housing 112 about the shaft 104. These movements are effected hydraulically by a hydraulic cylinder 121 reciprocating over a piston 118 secured to the housing 112 by admitting pressure fluid alternately to its opposite ends. A roller 124, Figs. 11 and 14, carried by the cylinder co-operates with an inclined cam surface 125 and adjoining cam surface 126 on the slide 105, the surface 125 being settable at different inclinations: a hydraulic plunger 129 acts between the slide 105 and housing 112 to urge the roller 124 into engagement with the cam surfaces. During the initial leftward movement of the cylinder 121 in Fig. 11 the inclined cam surface 125 acts on the roller 124 to pivot the housing 112 about the shaft 104 and so carry the diamond across the tip surface 100. A rack 135 slidable along the axis 115 in the tubular part 114 of the bracket 113 is then urged leftwards in Fig. 11 by the engagement of a button 134 on the end of the rack 135 by a member 122 on the moving cylinder 121 and, through pinion-and-rack gearing 136, 137, 138, Fig. 12. rotates the dresser arm 116 around the axis of the shaft 117; at this stage, the roller 124 engages a plane part of the cam surface 125 and so holds the housing 112 against pivotal movement. Pressure fluid acts upon a piston 147 fixed at one end of the tubular part 114 of the bracket 113 so as to urge the latter constantly to the right in Fig. 11 and is also applied to the rack in the gearing 136, 137, 138 for preventing back lash in the drive to the dresser arm 116. When in the continued movement of the cylinder 121, the abutment 134 passes within a nipple 144 at the end of the tubular part 114, the bracket 113 and rack 135 are moved axially as a unit and the diamond passes radially across the face 34 of the wheel; this face may be trued to a slightly dished or plane form depending upon whether or not the cam surface 126 is then set to cause the housing 112 to tilt about the shaft 104. The control circuit for the machine includes a solenoid valve which can be set to deliver pressure fluid to either end of the cylinder 121. Starting with the cylinder 121 in its left-hand position in Fig. 11 after a trueing operation. a new cycle is started by actuating a switch which serves through a limit switch closed by the cylinder 121 in its left-hand position to energize the solenoid valve to withdraw the cylinder 121 and re-set the ports to their initial position the pressure fluid connections are such that this stroke is carried out at rapid speed. Towards the end of this return stroke, a button 158, Fig. 11, on the cylinder actuates a piston valve 155 and so operates the piston 68, Fig. 5, to feed the grinding wheel through a distance determined by the stop plate 78. At the end of its stroke the cylinder actuates a second limit switch which acts to reverse the solenoid valve and so set the cylinder 121 into operation for a dressing stroke; the piston 68 is re-set to its inactive position by the piston valve 155 as soon as the button 158 withdraws with the cylinder. The rate of travel of the tool is equalized over its whole path, the operative stroke of the cylinder being comparatively slow (as determined by a throttle valve in the pressure fluid exhaust line from the non- driving end of the cylinder), while the tool is trueing the tip 100 and adjacent round and rendered even slower when the face 34 is being trued because the piston 118 then covers a bleed opening 131 in the cylinder. The solenoid valves of the trueing devices of the two wheels are controlled by a single switch. If desired, the control circuit may be modified to provide for the operative dressing stroke to be in the opposite direction from that described above. To provide a constant peripheral speed of the wheels as their diameters decrease, the motors 47 are controlled by a rheostat arranged in series with the field coils of an eddy-current clutch connected between an AC motor and frequency changer operating the motors 47; the feed movement of one of the heads 45 is used to act through rack-and-pinion gearing to adjust the resistance of the rheostat. The gearing acting upon the rheostat is arranged to close a switch and actuate a signal when the wheel diameter reaches a pre-determined minimum. Specifications 689,037 and 689,086 are referred to.