Patent GB-607702-A (GB)
Title: Improvements in precision measuring and positioning devices for tools or work tables of metal cutting machine tools
IPC: B23Q17/22
Filed: 1945-09-24
Abstract: 607,702. Gauging-devices; drilling. NILES.BEMENT-POND CO. Sept. 24, 1945, No. 24738. Convention date, Sept. 8, 1944. [Class S3 (iii)] [Also in Groups XXXVI and XXXVIII] In a spacing mechanism for a machine tool work table comprising a magnetic head with spaced poles, a circuit to magnetize the head, a magnetic member movable with respect to the head and means for indicating the relative positions of the head and the magnetic member, the head and magnetic member are mounted on relatively movable parts of the machine tool. A vertical drilling machine has a pillar 14, Fig. 1, carrying the adjustable tool spindle head 15 and a compound slide consisting of a work table 12 adjustable by a hand wheel 19, and a saddle 10 adjustable on a base 11 by a hand wheel 18. The invention is applied to both slides, but is described in reference to adjustment of the table on the saddle. A non- magnetic bar 20 slidably mounted in the lower surface of the table carries spaced inserts 28 of high magnetic permeability and may be adjusted relatively to the table by a nut 22, Fig. 3, engaging a screw 21 rotated by a hand wheel 26 through gearing 23, 24. A bar 32 slidably mounted in the upper surface of the saddle carries a magnetic head 30 and may be adjusted relatively to the saddle by a micrometer device comprising scales 38 and 56, a knob 58 and a spindle 52 which engages a nut 50 connected to the bar 32 with limited flexibility by an intermediate bar 34. The bar 34 may be clamped in position by a rod actuated by a handle 27. To prevent damage when the micrometer spindle is at its extreme positions, the knob 58 rotates the spindle 52 through a spring detent 60 engaging notches on the inner face of the knob. The magnetic head 30 comprises a central pole 42, Fig. 7, and two spaced poles 40, the latter energized by coils 45, 46 supplied with alternating current from a transformer 60a. The coils are part of a Wheatstone bridge circuit including a rectifier 62 and indicator 48, and the circuit is balanced, as indicated by zero deflection on the indicator, only when the head 30 is centred directly under an insert 28 or is midway between two inserts. To cut out this latter zero reading, a switch 63 is operated by an arm 64, Fig. 6, carrying a roller 66 which engages spaced recesses on the bar 20 so that the switch is closed to shunt the coil 45 and unbalance the circuit except when the head 30 is approaching a central position under an insert 28. In use, the work table is first positioned for drilling the first hole, the micrometer set to the zero position and the bar 20 adjusted by the hand wheel 26 so that an insert 28 is directly over the magnetic head ; the bar may be clamped in this position by a binding screw and handle. The table 12 can then be adjusted step-by-step in accordance with the spacing of the inserts. To obtain spacings of a fraction of the distance between inserts, the magnetic head is adjusted by the micrometer to the required fractional distance from an insert and the table adjusted by the same distance to bring the insert over the head.