Patent GB-275479-A (GB)
Title: Improvements in or relating to the electrical operation and control of metal cuttingand like machine tools
IPC: B23Q35/32
Filed: 1927-01-07
Abstract: 275,479. Shaw, J. C., and Shaw, R. D. Jan. 7, 1927. Milling-machines.- A tracer which is adapted to follow the outline of a model or pattern and control electromagnetic clutches which operate two rectilinear feed-screws for reproducing the model by means of a milling-cutter comprises two fixed electrical contacts and two movable contacts which are controlled by means of a tracer-spindle which is mounted for universal lateral movement. The tracer comprises a head 1, Fig. 3, in which is secured a tubular body 2 having a ball joint 4 for supporting the spindle 3 which has an interchangeable end 8 for engaging the pattern and a button 11 for operating the electrical contacts. The fixed contacts consist of adjustable screws 60, 61, Figs. 1 and 5, having contact points 57 normally engaged by contact points 48 on levers 40, 41 which carry the movable contacts 45, 46 and are drawn together about their pivots 39 by a spring 66 so as to close the contacts 57, 48. The levers and contacts are mounted on an insulating block 18 through which the spindle 3 extends, the levers being insulated from each other by a link 66<a> on the spring 66. The contacts 48 are mounted in insulating bushes on the levers and are connected by wires 5, 56 to two segments C, B, Fig. 5, embedded in the insulating block 18. Two other segments A, D, carry the pivots 39 of the levers 40. 41 and are thus in direct electrical continuity with the contacts 45, 46, respectively. The block 18 is rotatable so as to bring each segment into engagement with one of four carbon brushes 68, Figs. 1 and 5, spring pressed at 69 and slidably mounted in insulating bushes 68a carried by the fixed head 1 of the tracer. The four brushes 68 are connected as shown in Fig. 5 with electromagnets 72, 77, 87, 88 and with a low-tension generator 75, the magnets constituting relays which operate switch arms 78, 91 for controlling the high-tension electromagnetic clutches 80, 86, 94, 95. The tracer-spindle is earthed through the frame of the machine and is normally maintained by a spring 65 in engagement with the contacts 63, 64, so that when its end 8 is not in engagement with the pattern two of the clutches such as N, W or S, E &c. will be energized to traverse the cutter and tracer in a N.W. or S.E. &c. direction, the particular direction being selected by rotating the segments into contact with different brushes. This rotation is performed by bevel gearing 22, 31 and a handle 35 having a pointer 34 co-operating index studs 33, the handle and pointer making an angle of 45‹ with each other. The arrangement is such that the contacts 63, 64 each control a recilinear feed in one direction while the contacts 45, 46, control the feeds in the reverse directions. To copy a pattern such as a, Fig. 4, the pointer 34 is set about 40‹ from the NW stud 33 in a clockwise direction, so that the normal traverse will be in a NW direction but as the tracer moves from 1 to 2 the spindle will be oscillated and the circuit through 63 will be broken while that through 64 will be maintained. The W feed will consequently be stopped but the N feed will continue until the spindle has been rocked far enough to close the contact 46 and thereby actuate the E feed and traverse the tracer from 2 to 3. As the pressure on the tracer is relieved the contact at 46 will be broken and the N feed alone will operate, the E and N feeds continuing intermittently in very small steps until a point 6 is reached when the N feed will tend to carry the tracer off the pattern, thus permitting the contacts 63, 64 to close and introducing the NW feed again. On engaging the pattern again at 8 the contact at 63 will be broken and the N feed alone will operate, the traverse then continuing alternately N and NW until the NW traverse becomes tangential to the pattern at A, when the pointer 34 must be rotated so as to provide a SW feed when the contacts 63. 64 are both closed. Should the movement of the button 11 from either of the contacts 63, 64 fail, from electrical or mechanical reasons, to break the circuits to the respective clutches, continued movement of the tracer will rock the spindle so as to oscillate one or both of the levers 40, 41 and definitely break the circuit at 48, 57, thus providing a mechanical interlock. The operation of the tracer in following completely round a closed pattern, either internally or externally, is also described in the Specification. Balancing parts.-The spindle 3 of the tracer is balanced by a plunger 13, Fig. 3, supported at the bottom of the body 2 by a spring 14 adjustable at 15. Specification 233,747 is referred to.