Patent GB-1075931-A (GB)
Title: Improvements relating to machine tools
Inventor: FIRTH DONALD
IPC: B24B47/06
Filed: 1964-04-22
Abstract: 1,075,931. Grinding; gauging devices. NATIONAL RESEARCH DEVELOPMENT CORPORATION. May 14, 1965 [April 22, 1964], No. 16582/64. Headings B3B and B3D. A system for controlling a machine tool, such as a grinding machine, having a fluid pressure motor for causing relative cutting movement between the cutting tool, which may be of the rotary or reciprocatory type, comprises means responsive to a rise in the pressure difference between the fluid inlet and output of the motor whereby to provide a zero point or reference from which the total depth of cut may be observed, or may be preset by adjustment of means limiting the feed movement. As described, the machine tool has a grinding wheel 10 which is driven by a ballpiston motor 11, such as described in Specification 906,553, connected to a high-pressure supply line 15 and a low-pressure line 16. The motor 11 is carried by an hydraulic fine-feed device 14 which is mounted on a carriage 12 movable to move the grinding wheel 10 towards and away from a workpiece 13, the fine-feed device, which may be as described in Specification 1,018,436, having a pressure vessel which has at least one dimension controllable by the pressure of the fluid therein to vary the strain below the elastic limit of the vessel, the fluid being supplied from a high-pressure line 17. The maximum pressure supplied to the fine-feed device 14 is determined by a feed magnitude controller 18 and the rate of cut is controlled by a rate controller 19. The magnitude controller 18 has a bore 21 which is connected to the supply line 17 and has a piston 22 engaged by a spring 26 which can be adjusted by a handle 29 to control the flow from the bore to outlets 30 connected to exhaust. The rate controller has a bore 34 containing a valve spool 35 which, at one end, is subjected to the pressure in a line 36 connected to the supply line 15 and the motor 11, and at the other end is subjected to the pressure of a spring 38 adjustable by a handle 40 and to the pressure in a line 37 connected to the low-pressure line 16 of the motor, the valve spool being responsive to the pressure differential in lines 25 and 16 to control the flow from the line 17 to a line 43 connected to the fine-feed device 14. The spool also controls the flow from a low-pressure line 47 to a line 48 connected through a flow indicator 50 to an exhaust line 49, the indicator being in a pressure gauge 32 connected by a line 31 to the high-pressure line 17. The dimensions of the spool 35 are such that fluid cannot flow from both lines 17 and 47 to lines 43 and 48 simultaneously. In operation, the motor 11 is driven by the supply from line 15, the carriage 12 is moved, for example by a linear hydraulic drive as described in Specifications 924,906 and 961,339, to move the grinding wheel to within say 0.0005 inch of the workpiece, and the controller 18 set at some low value insufficient to expand the chamber of the fine-feed device 14. The handle 40 of the feed rate controller 19 is then rotated until an edge 51 on the spool just stops flow from line 47 to the flow indicator 50. The position of the handle represents a zero rate of feed and can be moved from this position to a position indicated by a graduated scale for a predetermined rate of feed. The handle 29 is then rotated to compress the spring 26 so as to increase the pressure supplied to the fine-feed device which expands to engage the grinding wheel with the workpiece, such engagement altering the pressure difference between lines 15 and 16 across the spool which is thereby moved, the rotation of the handle then being stopped in a position representing a zero depth of cut; the reading on the pressure gauge 32 then represents also a zero depth of cut. The handle 40 is then rotated to give the desired rate of cut and the handle 29 rotated until the pressure gauge indicates the required depth of cut, cutting continuing automatically at the desired rate until the required depth has been reached. In another embodiment, the pressure gauge is replaced by a marker co-operating with a graduated scale.