Patent GB-813071-A (GB)
Title: Improvements in electric spark discharge type drilling and boring machines
IPC: B23H7/28
Filed: 1956-12-31
Abstract: 813,071. Cutting by spark erosion. CINCINNATI MILLING MACHINE CO. Dec. 31, 1956 [Jan. 10, 1956], No. 39617/56. Class 83 (4). [Also in Group XXXV] A spark-erosion drilling and boring machine comprises a tool head 9, Fig. 1, having its axis substantially normally to the surface of a work-table 8, a telescoping sleeve assembly 72, Fig. 10, journalled in the head for rotation about its axis and including a plurality of non-concentric sleeves 73, 76, 78 and an axially movable spindle 80, for carrying the cutting electrode 11, mounted in the inner sleeve 78, the sleeves being relatively angularly adjustable for varying the axis of the electrode relatively to the axis of the head to cause the electrode to generate a surface of revolution upon rotation of the assembly. The lower end of the spindle 80 carries a chuck 83, Fig. 22, for the electrode. Relative rotation of the outer and central sleeves 73, 76 by means of a knurled wheel 90, causes tilting of the spindle and electrode, Fig. 21 (not shown); relative rotation of inner and central sleeves 78, 76 by means of a knurled knob 94, causes eccentric movement of the spindle and electrode relative to the axis of the sleeve assembly. The sleeves are locked in their adjusted positions by screw 93, Fig. 10 and screws 100, 101, Fig. 22. The electrode may be solid or hollow and is preferably made of brass; it is normally rotated during cutting and may be used for drilling blind or through holes in a workpiece 12, Figs. 2, 4 (not shown), disposed in a tank 236, Fig. 1, filled with a dielectric liquid 235 from a storage reservoir 234 by a pump 237 which supplies the dielectric through hose 238 to a hollow shaft 140 coupled to the hollow spindle 80 and hence to the electrode. The electrode may be hollow and externally threaded, Fig. 5 (not shown), for forming threaded bores. Eccentric adjustment e, Fig. 7, of the electrode, with simultaneous rotation R and forward feed F of the electrode and rotation of the sleeve assembly causes the threaded electrode to produce a larger internally-threaded bore in the workpiece. A plain electrode, Fig. 6 (not shown), may be used to form a similar plain hole. By additionally tilting the electrode, Fig. 8, a conical hole will be generated; the hole may be threaded by using a threaded electrode. The worktable 8 is slidable on a saddle 7, slidable transversely on a knee 6, slidable on a fixed column 5 whereby the workpiece 12 has three directions of movement. The complete head 9 may be tilted by a screw 231. The electrode spindle 80 may be power driven by an electric motor 124, Fig. 16, through belt 127, shaft 125, clutch 128, gearing 136, shaft 137, gearing 138, Fig. 10, shaft 140 and universal coupling 143, 144, 145; clutch means 197, Fig. 16, are provided for reversing the rotation of the electrode. Alternatively the spindle may be driven manually by a hand wheel 151, Fig. 16, which incorporates an interlock for disengaging the clutch 128. The sleeve assembly 72 may be power driven by an electric motor 102, Fig. 10, through gears 103, 104, worm 105, Fig. 16, clutch 114 and gearing 116, 117, Fig. 11 (not shown), driving toothed gear 118 on the outer sleeve 73; alternatively the sleeve assembly may be driven manually by hand wheel 119, Fig. 16, whose operation automatically disengages the power drive. The feed is normally effected automatically by a servomotor 155, Fig. 16, responsive to the spark gap voltage, through change-speed gearing 157, 158, 159, 160, selected by shifter 162, change-speed gearing 164, 165, 167, 168, selected by shifter 163, gear 171, bevel gears 173, 174, changespeed gear-box 175, Fig. 14 (not shown), gear 178, Fig. 10, clutch 182, shaft 183, gears 185, 186, and screw 141. The latter is axially fixed and moves a non-rotary nut 187, 189 connected through bearings 190 and sleeve 142 with the spindle 80. The feed may alternatively be effected manually by a hand wheel 193, Fig. 1, whose operation automatically disengages the clutch 182 of the servomotor feed. The spindle 80 and electrode may also be rotated automatically from the feed servomotor 155 by engagement of clutch 207, Fig. 16 which automatically releases clutch 128. The sleeve assembly may also be driven automatically from the feed servomotor by the engagement of sliding clutch member 114 with clutch member 113 whixh automatically disengages the sleeve drive motor. Thus rotation of the electrode and/or rotation of the sleeve assembly may be co-ordinated with the feed. The spark gap between electrode 11 and workpiece 12, Fig. 23, is in parallel with spark capacitors C<SP>1</SP> controlled by manual switches SW-2 for selecting the required capacitance and is connected with a D.C. power supply M.400 employing electronic devices which control the pulse width and interval between pulses, and fed from a rectifier RE-1 and transformer T-1. The positive potential on the workpiece 12 acts on one terminal G of the servomotor armature A-1, the other terminal B being fed with a reference voltage from a rectifier RE-2 and transformer T-2. When the operation is started by a switch PB 3, Fig. 24 (not shown), the servomotor is rotated quickly due to the potential difference between terminals B, G to feed the electrode to the work. A microswitch actuated by the electrode then inserts braking resistor R-3 and subsequently resistors R-4, R-5, into the armature circuit and normal sparking proceeds with feed controlled by the armature. When the electrode reaches a predetermined depth it actuates a limit switch 2LS which stops the voltage supply on terminal G and causes the armature A-1 to reverse and rapidly withdraw the electrode. The motors 102, 124 are controlled respectively by pushbuttons PB 8 and PB 7, Fig. 24 (not shown).