Patent GB-1117657-A (GB)
Title: Improvements in and relating to machine tools
IPC: B24B47/20
Filed: 1965-11-05
Abstract: 1,117,657.  Grinding. LANDIS TOOL CO. 5 Nov., 1965 [6 Nov., 1964], No. 46912/65. Heading B3D. A machine tool, such as a grinding machine, comprises a bed 10 having a workpiece support 20 and a support 15 upon which a cutting tool 16 is mounted and which is movable towards a workpiece W by a feed mechanism, a piston 91 and cylinder 92 movable relative to each other by movement of the cutting tool support, valve means operable before the end of a machining operation for directing fluid under pressure to the cylinder to arrest the advance of the tool support and place the feed mechanism under strain, and means 140 to reduce the pressure in the cylinder to relieve the strain gradually to permit continued movement of the cutting tool support in a controlled manner. The workpiece support 20 rotates the workpiece and a gauge 25 indicates the size of the workpiece. As described, the tool is a grinding wheel and is mounted on the support 15 which is movable relative to the bed 10 by a feed screw 30 having a piston 31 slidable in a cylinder 32 in the bed. A worm-wheel 40 is keyed to the feed screw and is rotatable by a worm 45 driven by a ratchet wheel 50 in one direction or the other by hydraulically operated pawls 51, 52. The grinding wheel is advanced during the grinding operation by a shaft 70 rotated by hand wheel 71 and formed with a worm 75 connected by wheels 76, 78 to the feed screw 30. A pinion 80 on shaft 70 is engaged by a rack driven by a piston 82. The wheel support has an abutment which engages the piston 91. An indicator 110 is provided to indicate the movement of the wheel support during finish grinding and has a feeler 115 engaging an arm 120 which is supported by a spring hinge 121 and connected by a flat spring 122 to a second arm 125 mounted on a spring hinge 126, the lower end of the arm co-operating with a stop adjustable on the bed 10. At the end of the rough grinding operation, a limit switch 7LS is actuated by cam 72 on hand wheel 71 and a solenoid-operated valve 150 is moved to connect cylinder 92 to pressure from pump P, the pressure being sufficient to prevent further movement of the wheel support. In this position, arm 125 engages stop 135 and the indicator 110 is adjusted to show the amount still to be removed from the workpiece. An infeed lever 143 is moved to depress a precision feed pilot valve having a notch 142 which permits a gradual change to a lower pressure in cylinder 92 to advance the wheel support at a rate proportional to the pressure, the operator observing the indicator 110 and gauge 25. If the feed mechanism does not have sufficient strain to advance the wheel support to the finish size, the lever 143 is moved to actuate a limit switch which actuates a solenoid-operated valve 151 to connect pressure to cylinder 92 to again hold the wheel support against movement which valve 160 is operated to move piston 65 and advance pawl 52 to rotate the lead screw 30 an increment and re-introduce strain into the feed mechanism, the wheel supports then being advanced again under the gradual reduction in pressure in cylinder 92 as lever 143 depresses the valve 140.