Patent GB-489308-A (GB)
Title: Improvements in and relating to gauging apparatus for machine tools
IPC: B24B49/04
Filed: 1937-01-25
Abstract: 489,308. Grinding - machines. NORTON CO. Jan, 25, 1937, No. 2199. Convention date, Jan. 23, 1936. [Class 60] In a cylindrical grinding-machine or other machine tool, a gauging device is provided comprising an electrode urged towards the work and electrically actuated means for controlling the feeding of the tool relatively to the work, the gauge being arranged so that when a predetermined size of work has been reached one gauge element is operative to stop the feed, and when the finished size of work has been reached, a second gauge element withdraws the tool from the work. The invention is described as applied to a cylindrical grinding-machine operating by the "plunge cut " method, the work 32 being carried by centres on a work table 24 on a carriage 23 movable on way 21, 22 on a base 20, and grinding being performed by a grinding-wheel 35 mounted on a wheel head 37 and driven by an electric motor 41. The slide 37 is movable on transverse ways either manually by rotation of a screw 46 and half nut 45 or automatically by axial movement of the screw by a piston 52 movable in a cylinder 53 ; the manual movement is produced, through gearing 59 ... 67 by a hand wheel 70. The carriage 23 may be moved by power, or by a hand wheel 75 through gearing. The gauging mechanism comprises two Y-gauge devices, one comprising upper angle plates 100 and lower plates 101 and the other comprising similar plates 100a and 101a. The respective pairs of plates are slidably mounted on slideways 105, 105a on opposite sides of support members 106, 106a, and the plates are moved together or apart by right and left handed screwed shafts 112, 112a, the parts being locked in adjusted position by wedge clamps 125, 125a, &c. The plates 101 &c. are made with detachable wearing surfaces of hard tool steel, tungsten carbide, tantalum carbide or boron carbide. The electrodes 102, 102a comprise a rod 102 mounted in a bore 130 in the part 106 bv means of insulating sleeves 131, 132, the rod being moved axially by means of a screwed part 135 thereon and a nut 134. An electric contact 140 is pressed bv a spring 143 against the rod 102, and in order to prevent short circuiting of the rod 102 to the work by cooling fluid, a rubber sleeve 144 is fitted on the end of the electrode rod, so as to act as a cup to exclude water, whilst a slot 146 is provided to drain away any moisture which gets into the cup. Pivoted on the member 106a is a lever 149, one end of which carries a splash plate 150 covering both rods 102, 102a and carrying a wiper 151 of rubber &c., the lever being rocked, when the member 106a, moves forward, by an inclined member 153 on the head 154 of a cylinder 164, so that the wiper engages the work 32. The cylinder 164 is carried by a support 157a adjustable, by a screw 161, on a slideway 156 on a bracket 155 secured to the base 20. In the base of the machine is a reservoir 168 from which oil is supplied by a pump 169 to a pressure line 170, and supported in the base is a valve casing 172 in which is movable, by a hand lever 176, a valve rod 175 carrying pistons 175a ... 175d ; the rod 175 is extended and has notches 177-179 therein for engagement with a spring-pressed detent 180, and the rod also is connected to a lever 183 pivoted at 184. A valve also is provided comprising a casing 186 containing a piston 189 having therein grooves 190, 191 and urged upwards by a spring 192. Fluid passes from the pump 169 to a pipe 200 leading to a port 201 in the valve casing 172, in which also is an exit port 202 leading by piping 203 to the front of cylinder 53, a shunt pipe 204 leading to cylinder 164 in which is a piston 205 connected to a cross head 207 in which the members 106, 106a are slidably supported. The cross head 207 carries forwardly extending portions 210, 211 carrying respectively a cylinder block 212 with cylinders 213, 214 and a block 215 with a cylinder 216. These cylinders have therein pistons 217, 218 and 221 respectively, cylinders 214, 215 being connected by piping 225 through a restricted orifice valve 224 to the line 200, and cylinder 213 being connected by a pipe 230 to the valve casing 186. The arrangement is such that the supports 106, 106a are at all times urged towards the work, and can follow this as it is reduced in size, but with the piston 205 in the position shown in Fig. 4, the gauges do not contact with the work ; also the right. hand gauge may be withdrawn prior to the left-hand gauge. The gauges are moved up to the work by moving the valve 175 so that the notch 178 is engaged by the detent 180 ; both sides of the piston 52 are then connected to exhaust, but the piston 205 is moved rearwardly, that is, towards the work, carrying with it the gauges. Grinding is started by moving the lever 176 so that notch 179 is engaged by the detent 180, fluid being then admitted under full pressure by pipe 240 to the cylinder 53 so that the wheel 35 is moved rapidly until it is just about to contact with the work, when a cam 263 on the piston rod 51 depresses a knob 265 on a screw in piston 189, thereby closing the poppet valve portion 270 almost on to its seating so that fluid passes only through a narrow slot 272, slowing down the feed of the wheel. When the work has reached a predetermined size, the electrode - 102 contacts with the work, thus allowing a small current to flow ; this is amplified and energizes a solenoid 275 to lower and close the valve 189 and also to allow fluid to flow to cylinder 213 to remove the gauge support 106 and its gauge from the work. Grinding then proceeds due to the spring of the machine parts, until the second electrode 102a contacts with the work, when a current flows causing a solenoid 282 to be energized, moving the lever 183 to carry the valve 175 to the left, thus causing removal of the wheel 35 and the gauge from the work ; a check valve 242 is provided so that during grinding the fluid flows through the restricted passage 260, but during movement of the wheel from the work fluid has an unimpeded flow through the valve. A valve 252 is provided for adjusting the rate of approach of the gauges to the work, so that the wheel 35 may be allowed to contact with the work before the gauges, for example, during rough grinding. The electric circuits controlled by the electrodes 102, 102a, which are identical. each comprises a thermionic valve 314, or 314a, having its filament fed by the secondary 310 of a transformer 307, the midpoint of the secondary being earthed. The grid 316 of the valve is connected by a condenser 318, shunted by a variable non-inductive resistance 319 and an inductance 321 to the electrode 102, and in the plate circuit of the valve is a tuned circuit 327, 328, a choke 331 and a relay 333 connected to the main 305 ; main 306 is earthed. When the electrode 102 contacts with the work, the grid 316 is earthed and the valve oscillates. thereby energizing the relay 333 ; the relay energizes a power relay 340 which closes the circuit of the solenoid 275 bv means of a switch 343 and similarly the relay 333a controlled by the electrode 102a causes the circuit of the solenoid 282 to be closed by means of a switch 343a. As the grinding-wheel approaches the work, and also recedes therefrom, a trip block 294 on piston rod 51 closes momentarily a switch 296, thereby energizing solenoids 353, 353a to open the switches 343, 343a. The bracket 157a may be made of steel or malleable iron to allow it to be bent slightly so as to bring the central plan of the gauging heads to a position wherein they will adjust themselves readily to the work. The plates 100, 101, 100a act as steady rests for the work since they are urged against the work by the fluid pressure ; the work may be traversed axially past the grinding-wheel. In a modification, the electrode is replaced by a spring-pressed rod carrying an insulating tip, for example, of boron carbide, and the casing holding the rod contains an insulated plug connected to the valve grid as described. When the rod is moved to contact with the plug, the grid is earthed and operation of the machine follows as described above.