Patent GB-515656-A (GB)
Title: Improvements in or relating to electric feeler controls for machine tools
IPC: B23Q35/12
Filed: 1938-06-24
Abstract: 515,656. Copying milling-machines. MULLER, E. F. June 24, 1938, No. 18839. [Class 40 (iii)] [Also in Groups XXII and XXXVIII] In an electric feeler control for machine tools such as milling-machines, a two position feeler operates the feeler feed alternately in opposite directions and also indirectly controls the longitudinal feed so that the latter is interrupted when the feeler displacement in either direction exceeds a predetermined amount. The machine comprises a column 1 carrying a spindle head 2 and a vertically movable knee 8 carrying a compound slide 9, 10. The cutter spindle 63 is driven from an electric motor 4 through variable speed belt pulleys 6 and is clamped in a vertically adjustable fixed position in the head 2. The electric tracer mechanism 66 &c. is rotably adjustable about a rod 60 and the latter is horizontally adjustable on an arm 61 secured to the head. The upper table 10 carries the work A and a table 11 carrying the pattern is finely adjustable thereon by means of a screw 64. The vertical copying movement of the knee 8 and table 10 is derived from a reversible motor 12 or from a uni-directional notor and reversing gearing, the drive being through pivoted casings 15, 18, Fig. 2, worm gearing and -a shaft 16 to bevel gearing 19, Fig. 1, which rotates the vertical knee screw 20. The longitudinal feed of the table 10 is derived from a motor 26 which drives a horizontal shaft 48 through variable belt gearing 27, a worm drive 29 and a friction clutch 31 which is set to slip at any predetermined overload by neans of a nut and spring 33. The shaft 48 s connected by a flexible shaft 50 to bevel and spur gearing which drives the table screw 54. The tracer consists of a spindle 66 carrying a disc 65, Fig. 11, rounded at the edge to permit t to oscillate, and engaging a flexible diaphragm 69. The latter is clamped by a cover 67 to an insulating casing 70 containing nercury into which dips a screw 72, Figs. 11 and 12, connected by a lead to the current supply. In operation, the table 10 is reciprocated horizontally by the motor 26 vhich is reversed at each end of the stroke by tappets 35 on the table engaging push switches 37 connected to the reversing switch 79, Fig. 12, and during this longitudinal traverse of the ;able the knee 8 is given a cyclic up and down novement. In the condition of the tracer shown in Figs. 11 and 12 the knee is fed upwards by the motor 12 but when the pattern engages the tracer the spindle 66 is raised, displacing the diaphragm 69 and causing the mercury to nake contact with a screw 73, thus energizing a relay 76. This energizes the reversing switch 77 for the motor 12 and lowers the table until contact with the screw 73 is broken, and the up and down cycle with constant longitudinal feed continues so long as the pattern presents a horizontal surface. An arm 40, Figs. 1 and 12, mounted by means of a friction clutch 43 on a shaft 22 connected by bevel gearing 19 to the drive for the screw 20 is adapted to oscillate between contacts 44, 45, without touching them so long as the surface remains horizontal, but if the tracer meets a cavity in the pattern the lever 40 will be swung far enough to engage one of the contacts and thereby energize an electro magnet 25. This rocks a brake lever 38 and causes it to engage the teeth of a disc 34 keyed to the shaft 48 and so stops rotation of the screw 20, the friction clutch 31 then slipping. The upward feed of the knee can then continue alone until the tracer engages the base of the cavity, whereupon contact is made at 73, the motor 12 is reversed, the lever 40 is swung away from its contact 44 or 45, the solenoid 25 is de-energized and a spring 39 removes the brake 38, thereby allowing the previous cycle to continue. If the tracer meets a protuberance on the pattern the combined downward and longitudinal feeds are unable to free the tracer from the pattern and consequently the lever 40 engages the other contact and energizes the solenoid 25 to stop the longitudinal feed until the downward feed has relieved the pressure on the tracer. The combined upward and longitudinal feeds then alternate with the downward feed alone until the protuberance has been surmounted. After each stroke of the longitudinal feed the slide 9 is automatically traversed laterally by means of a screw 95 to cause the next cut to be taken on - a parallel path. In order to protect the motor 12 from excessive heating on reversal, resistances 78 are placed in each phase of the three-phase circuit. Should the motor 12 not be reversed when the mercury in the tracer meets the contact 73 the knee 8 will continue to ascend until the mercury meets a further contact 74 which energizes the solenoid of a main cut-out switch 75 and stops the machine. The switch 75 also includes a bi-metallic device which operates to open the switch when excessive current is used by any part of the machine. A limit switch 58 on the knee 8 is adapted to engage a stop 59 on the cross side 9 to actuate the stop switch 75 when the cross slide has traversed a predetermined distance and thus stop the whole machine. If the motor 12 is not to be reversed, the clutch of a reversing gear for the drive to the screw 20 is operated by a solenoid under control of the tracer contact 73. For producing edge cams &c. from a sheet template the work and pattern are secured to rotary tables 86, 87, Fig. 10, adapted to be rotated in unison by a worm drive from a shaft 93 driven by a flexible shaft and gearing from the motor 26, this rotation replacing the longitudinal feed of the table 10. The tables are supported vertically on an angle bracket on the table 10, which remains stationary, and the' cutter 62 is mounted on a short horizontal shaft driven through bevel gears from the spindle 63. The tracer spindle 66 is also adapted to operate in a horizontal position and the operation of the machine is similar to that described above, except that the up and down movement of the knee controls the rotation of the work and pattern, instead of their longitudinal traverse, through the brake 38. In a modified method of producing edge cams, without rotation of the work and pattern, the latter are mounted stationarily in a vertical position on an angle bracket on the table 10 and the tracer is caused to follow the upper edge of the pattern by vertical and horizontal feeds, with an upward bias of the vertical feed, whilst the lower edge of the pattern is followed with a downward bias, caused by reversing the polarity of the motor 12 with a hand-set reversing switch 94. For taking roughing cuts the contacts 44, 45 may be set relatively far apart but for finishing they are set close together and the rate of longitudinal feed is reduced. An excessive rise of pressure in the tracer due to displacement of mercury is prevented by providing an enlargement 71 therein into which the air may be compressed. The copying mechanism may be an attachment to an existing milling-machine. Interlocking hand and power feeds.-The worm drive 17 for the knee elevating screw 20 may be disconnected from its shaft by a clutch controlled by a handle 24, Fig. 1, to allow hand rotation of the screw by means of a hand wheel 23, and similarly a clutch in the drive to the table feed screw 54 may be disconnected bv a hand lever 55 to allow manual rotation of the screw.