Patent GB-387436-A (GB)
Title: Improvements in automatic feed for grinding or abrading machines
IPC: B24B19/06
Filed: 1931-11-06
Abstract: 387,436. Feed control for grinding- machines. VAN NORMAN MACHINE TOOL CO., 160, Wilbraham Avenue, Spring- field, Massachusetts, U.S.A. Nov. 6, 1931, No. 30850. Convention date, Nov. 17, 1930. [Class 60.] Round holes, enlarging and trueing ; gauges.- An automatic feed control for a grinding or abrading machine, particularly an oscillating grinder for making outer races for ball bearings, comprises a work-gauging device which is arranged when the work attains a predetermined size to close electrical contacts to cause actuation of the feed control, this actuation causing a switch in the circuit to be automatically opened so that the contact devices may be subsequently separated without arcing. The machine is provided with an oscillating work-head 31 mounted on a spindle 32 connected by a link 34 to a crank pin 35 mounted on a driven shaft 36. The head carries an adjustable horizontal slide 38 supporting the work-holder 40, the workpiece 43, which is of the double-race type, being mounted on a spindle 41 driven by a belt 44. The main frame also carries a slide 45 adjustable to and from the work by a handle 46, and provided with a lower cross slide 48 operated by a screwed shaft 50 carrying a feed ratchet wheel 52. The cross slide is formed with ways 53 for the rough positioning of the tool head 54, carrying the grinding-wheel 56. The gauging mechanism is carried on the workholder 40 and consists of a bracket 60 carrying a spindle 62 terminating in a member 63 having trunnions which support a carrier 65. A tube clamped to this carrier carries an inner rod 68 which forms a connection between the work contact and the indicating device. The lower end of the rod carries a split clamp which grips a diamond holder 78 while another clamp 80 carries a second diamond holder 81. These diamonds are used alternatively, their holders being of different lengths and being arranged to engage respectively in the inner and outer races of the work-piece 43. The rod 68 is moved through 90‹ to bring one or other diamond into position by means of a loose handle 84 which entrains a rod 85 secured to the rod 68. Besides this angular motion of the rod 68 the entire follower mechanism may be swung on the trunnions 64 and is latched in the operative position. A stop screw locates the operative diamond exactly in the centre of the race. In order to operate the electrical contacts from the diamond points the motion of the diamond and of the rod 68 is amplified by mechanism embodying a visual indicator which comprises a rod 103 operatively connected to the dial mechanism and resting on the upper end of the rod 68. The upper end of the rod 103 rests against a screw carried by a bracket 107 secured to a rod 108 which has rack teeth acting through a multiplying gear train to rotate a pinion 117 on a shaft 118. The shaft 118 carries cams 124, 125, coacting respectively with contact levers 126, 132 which are held by springs against their respective cams. When the lever 126 slips off the high part of its cam it engages an electric contact 129 while the lever 132 similarly coacts with a contact 137, Fig. 6. The contact lever 132 has an eccentric pivot 134 whose adjustment 'is indicated by a scale. The arrangement is such that when the work attains a predetermined size the lever 132 slips off the high part of the cam and changes the coarse feed to a fine feed which continues until the lever 126 also drops and causes the feed to be stopped. Means are provided for lifting the levers 132, 126 and resetting the cams when the diamond is positioned in a fresh work-piece. In order to avoid chattering and consequent disturbance of the gauging mechanism, a dashpot, Fig. 4, is provided to restrain the movement of the rod 68. Upward movement of the rod is only permitted as fluid leaks past the piston 158 in the cylinder 157. Downward movement of the rod is unrestrained, the dashpot piston being lifted by a spring 159 and the ball valve 164 opening automatically to permit fluid to flow from one side of the piston to the other. The cross-feed of the grinding- wheel is effected from a cam 170 on the shaft 36 which acts through a push rod 171 on a pivoted plate, which in turn actuates a tappet 175 whose upper end engages an arm 177 connected to the pawl 183 which operates the feed ratchet wheel. In order to regulate the feed a wedge member 189 may be positioned beneath the tappet 175. This decreases the lost motion between the tappet and pawl arm and gives the coarse feed. The wedge member 189 is carried on an arm 186 pivoted at 185. For stopping the feed a lever 191 pivoted at 192 carries an extension 194 which when the lever end 193 is rocked downwardly, engages a pin 197 to lift the pawl clear of the ratchet wheel. The arms 186, 191 are normally held up by latches controlled by the gauging mechanism. For the lever 193 a hook 212 on the lever engages a latch controlled by a solenoid 206 in the electric circuit, Fig. 6, so that, the tumbler switch 220 being closed, when the lever 126 drops off its cam and closes the contacts 128, 129, the solenoid is energized to trip the latch and allow the lever 193 to descend and stop the feed. Similar latch mechanism acts in conjunction with the lever 187 for changing from the coarse to the fine feed. During its descent, the lever 193 opens the tumbler switch 220 in circuit with the contacts 128, 129 while the lever 187 similarly opens a switch 223 in circuit with the contacts 137, 138. In this way the circuits are broken before the gauging contacts are broken for resetting the gauging mechanism and thus arcing at the contact points is prevented. After the feed has stopped the machine is preferably allowed to continue the grinding operation until sparking has ceased.