Patent GB-686257-A (GB)
Title: Improvements in or relating to automatic stop mechanism for grinding machines
IPC: B24B49/04
Filed: 1950-04-18
Abstract: 686,257. Grinding. NEW ALL ENGINEERING CO., Ltd., and HOARE, S. W. April 5, 1951 [April 18, 1950], No. 9539/50. Class 60. Automatic stop mechanism for a grinding machine wherein a floating three - point - contact gauge having a movable feeler is connected by a magnifying mechanism to a movable member of a visual size-indicator for the work is characterised in that the movable member of the visual size-indicator carries an electrical stop contact for modifying an electrical stop circuit and so stopping the machine when a piece of work in the machine reaches a predetermined size. A cylindrical grinder is provided with a floating fitment 11 comprising a hollow stem 12 carrying at its lower end a bracket member 13 extending around the work 14 on the opposite side to that which is engaged by the grinding wheel 15. The bracket 13 carries two fixed anvils 16, 17 and the stem 12 contains a sliding anvil 18. The fitment is supported on a spring arm 19 carried on the grinding wheel guard 20, the spring arm urging the anvil 16 upwards; the fitment is pivoted on the arm at 21 so that the anvil 17 is pressed yieldingly against the work. The sliding anvil 18 is carried by a slide 22 pressed downwardly by a spring 23 and engaging a lever 24 which presses on the feeler 25 of a dial indicator 26 having a dial 27 over which moves a pointer 28. The dial indicator 26 is adjustable on an inclined dove-tailed slide 80 on the stem 12 by a screw 82. Around the dial 27 is a bezel 29 rotatable relative to the dial; the bezel carries an insulated contact 31 carrying a spring contact 32 and a second contact 33 is mounted on the pointer 28. The contact 32 is connected by line 34 to the tractive coil 35 of a relay which, when energised, closes double-pole contacts 36, 37 in a circuit of solenoid 38 connected by lines 39, 40 to the supply lines 41, 42 of the electric motor 43 of the workhead. The solenoid 38 has a core 44 which operates, through a lever 45, a valve 46 controlling the hydraulic operation of a piston 49 which surrounds the nut 50 of the feed screw 51 for putting on cut for the grinding wheel 15. The arrangement is such that when the solenoid 38 is energised by the action of the limit contacts on the floating indicator and relay 35 the grinding wheel is withdrawn from the work. To restart the machine, the operator pushes over starting lever 56 which, through rod 55, reverses the valve 46 thereby advancing the grinding head 54 to bring the grinding wheel 15 into contact with the new work. A feed-wheel 63 rotates, through gearing 65, 66, the nut 50 which is rotatable in the piston 49 and works between thrust races 67, 68 thereon. The feed-wheel 63 is operated automatically by a piston 60 the rod 61 of which carries a rack 62 geared to the wheel 63; the piston 60 works in a feed-control cylinder 59 connected by pipes 57, 58 to the two sides of the hydraulic circuit between the valve 46 and piston 49. When the nut 50 is retracted by the piston 49 it is also given a rotation by the feed control piston which causes it to retract the feed screw 51 still further, and when the operator actuates the starting lever 56 to reverse the valve 46 the grinding wheel 15 is not advanced fully but only to the position in which it will commence operations upon the work. Thereafter it has to be further advanced by rotation of the nut 50 and this is effected automatically by fluid admitted by pipe 57 to the bottom end of feed control cylinder 59. This admission of fluid is controlled by a screw down needle valve 69 so that the rate of movement of the piston of the feed control cylinder may either be set to a rate suitable for continuous plunge feeding or limited to one which is suitable for advancing the wheel at such a slow rate as, when traverse grinding is being effected, will put on a small cut per reciprocation of the work table. To permit rapid ex- .haust from the lower end of the feed control cylinder when the grinding wheel is withdrawn from the work the needle valve 69 is by-passed by a non-return valve 71. The starting lever 56 is connected to a switch 72 connected by line 73 to operating coil 74 of a magnetic switch controlling the motor 43 for driving the workhead, so that rotation of the work is initiated automatically when the grinding head is advanced towards it and is interrupted automatically when the solenoid is operated to retract the grinding head. The tractive coil 35 of the relay for operating the solenoid 38 is actuated from the secondary 75 of a step down transformer 76 connected in parallel with the solenoid operating contacts of the relay 35. The transformer 76 and the solenoid operating contacts 36, 37 are connected by lines 39, 40 as a branch to the supply for the motor 43 which drives the workhead. Thus the whole of this circuit is only alive while the grinding cycle is in progress but is automatically reconnected by the operation of the switch 72 and coil 74 when the lever 56 is operated. Specification 440,803 is referred to.