Patent GB-806629-A (GB)
Title: Process and apparatus for dressing grindstones
IPC: B24B53/08
Filed: 1957-06-21
Abstract: 806,629. Dressing grinding wheels. FORTUNA-WERKE SPEZIALMASCHINENFABRIK A.G. June 21, 1957 [Nov. 17, 1956], No. 19583/57. Class 60. A method of dressing a profiled grinding wheel consists in traversing a dressing tool 37 carried by a spindle 7 in one direction over the grinding wheel under the control of a tracer 12 engaging a template 18, retracting the spindle to a rest position, rotating the spindle through 180 degrees so as to incline the tool at a different angle, moving the spindle from the rest position to bring a second tracer 13 into engagement with a second template 19, and then traversing the tool in the opposite direction. The dressing tool 37, such as a diamond, is carried by a spindle 7 which is vertically-reciprocable by a piston- and-cylinder device 9 in a guide 4 mounted on a slide 3 horizontally-reciprocable by a piston- and-cylinder device 25, 56 on guideways on a carrier 1. The tracers which are inclined to each other at an angle of 60 degrees, are hydraulically operated in their guides 10, 11 on a carrier 8 attached to the spindle 7 so that when one is projected from its guide to its operative position, the other is retracted, and, on successive lowering movements of the spindle 7, the two traces are alternately operative upon their respective templates 18, 19 carried on the carrier 1. The piston-and-cylinder devices 9, 56 are included in a hydraulic circuit which, as shown in Fig. 3, also comprises a reversing valve 20b controlling the devices 9, 56 for raising and lowering the dressing tool and tracer carrier and the reciprocation of the slide, a control valve 20d which causes rotation of the spindle through 180 degrees at each end of the horizontal movement of the slide 3, and a control valve 20a, the piston of which carries a roller 23 engaging a control rail 22 on the slide. When the dressing process is initiated, the piston 49 common to the valves 20b, 20d is moved to cause fluid pressure from a pump 30 to urge the tracers 12, 13 to operative and inoperative positions, respectively, actuate a rotary piston 5 to rotate the spindle 7 through 180 degrees, and, by means of the device 56, move the slide 3 to the left. During this movement of the slide, the roller 23 moves from a rest position 45 in the rail 22 to an operative level 46 whereupon the disconnection of fluid pressure from the device 9 results in the tracer carrier 8 and spindle 7 being lowered until the tracer 12 engages the template 18 and the diamond is in its operative lower position. The speed of the slide is controlled by a throttle 21 in a valve 20c until, when the tracer reaches a descending part of the template, such as when radiusing the edge of the grinding wheel, an adjustable cam 75 on the slide 3 moves the piston 42 of a throttle valve 28 to increase the pressure at the putput end of the cylinder 56 and slow the movement of the slide. When this part of the dressing is completed, the speed is again increased until the movement of the slide causes the roller 23 to rise towards the level 47 on the rail 22. When the roller reaches a height corresponding to the level 45, the valve 20a serves to reconnect the device 9 to the fluid pressure and the tracer carrier and spindle are raised. At the level 47, the roller causes the valve 20a to move the piston 49 of the valves 20b, 20d to reverse the pressure on the rotary piston 5 to rotate the spindle 7 through 180 degrees, interchange the tracers and connect fluid pressure to the opposite end of the cylinder 56 and also to the device 9. Dressing then proceeds in the reverse direction under the control of the tracer 13 engaging the template 19, the speed of the slide 3 being controlled by a second cam 76 as before. When dressing in this direction is completed, the roller 23 moves to the level 45 of the rail and the spindle and tracer carrier are raised to the rest position, the piston 25 moving to the end of the cylinder 56 or to an adjustable stop. When a plurality of wheels, which may be of different diameter, are to be dressed, a rapid motion may be given to the slide 3 in the intermediate positions between the wheels by different levels on the control rail 22 moving the roller 23 to connect the output end of the cylinder 56 directly to the sump 68 and so bypassing the throttle 21 ; additional cams are provided to slow the speed of the slide when the tracers engage the descending parts of the templates, which are formed with gradual inclines after these parts to bring the diamond back to the required height. To avoid errors in profiling due to temperature changes, the steepest parts of the templates are not less than 15 degrees from the perpendicular to the axis of the grinding wheel which, when the edges of the grinding wheel are radiused, causes a small portion of the profile to deviate from the circular path. During grinding, this portion is subjected to heavy loading and quickly wears to agree substantially with the correct profile. The tracers are spring-urged towards their operative positions to prevent damage due to possible failure of the fluid pressure.