Patent GB-233747-A (GB)
Title: Improvements in the electrical operation and control of metal-cutting and like machine tools
IPC: B23Q35/122
Filed: 1924-01-15
Abstract: 233,747. Shaw, J. C. Jan. 15, 1924. Milling-machines; cutter-slide feeds; reversing-mechanism.-In metal-cutting machine-tools in which screw feeds in three dimensions are provided for relative movement of the cutter and work, each screw is operated by an electric motor through electromagnetic clutches and electric relays and circuits under the control of a tracer. Alternatively the circuits and clutches may be controlled by hand. In a milling, engraving or die-sinking machine the cutter-spindle 113, Fig. 1, is mounted in a head 112 traversable along a transverse horizontal slide 109 vertically movable on a column 106 which is traversable along a horizontal slide 104. The column is traversed by a screw 163 driven through a twospeed reversing-clutch comprising electromagnets 130, 131, Fig. 6, continuously rotated in opposite directions by a motor-driven bevel pinion 127. A central shaft 137 carrying an armature 138 which may be connected to either magnet drives the screw 163, Fig. 7, by an electrically-operated sliding clutch 160 and bevel gears 150 (for a quick return), ,or a worm gear 147 and change-wheels 157 (for slow cutting feed). The magnetic clutch and gears are enclosed in a casing 154, Fig. 1, and similar driving and reversing mechanism for the vertical feed-screw enclosed in the column is provided at 218. A spindle 210 allows adjustment of the vertical screw by hand. The transverse horizontal screw 228 is driven from a motor 229 through a single-speed magnetic reversing clutch 230, but the brushes for supplying the rotating magnets are adapted to be swung to an inoperative position instead of being rigidly fixed as at 139 in Fig. 6. The traverse of the column in either direction is limited by adjustable dogs 200, Fig. 1, which oscillate a lever 197 and cause it to actuate a main reversing switch, a second set of contacts on the lever serving to break the circuit of the clutch in operation. A dog 225 on the cutter-head actuates a similar lever 222 through a rod 223 to reverse vertical motion by means of the same switch. Adjustable stop rods 311 carried by the cutter-head operate limit switches 307, 308 for the, transverse motion of the head. The arrangement is such that when the tracer is not in contact with the work, the clutch 130, 131 for traversing the column is inoperative, but a pair of interlocking switches is provided which permit the column to be traversed when the " in " limit switch has been operated and cause the column to be returned rapidly when the " out " limit switch is actuated. When taking heavy cuts with the cutter rotating against the feed, the cutter head has a quick-return traverse. Thus if the clutch 160 is at the left in Fig. 7 for slow horizontal traverse, on reversal by one of the dogs 200 the clutch is thrown to the right by a magnet energized by the reversing lever and simultaneously an interlocking switch is thrown to cut out the return traverse, while another switch is closed to withdraw the cutter-head from the work. This outward motion is stopped by the limit switch 307 and simultaneously the appropriate clutch is energized to produce the quick-return traverse of the column. At the next reversal the clutch 160 is returned to the left for slow traverse by a spring, the interlocking switch is again thrown and the cutter is fed to the work for another cut. All the movements of the machine are controllable from a push-button switch-board 266 within easy reach of the operator. The circuits and relays are operated at pressure of 12 to 15 volts to prevent burning of the contacts, but the magnetic clutches are operated on a direct lighting current of 110 to 125 volts. A pinion 159 on the low-speed feed train, Fig. 7, rotates a series of cam discs in a casing 179 through a two-speed change gear, the discs having different numbers of cam surfaces and each making, in each revolution, a number of electrical contacts with spring arms. The circuit of any one disc may be selected by a rotatable pointer 183 so as to cause the screw 163 to be rotated intermittently and provide a feed of the column at. each end of a vertical traverse of the cutter. A similar selector is provided at 220, Fig. 1, for intermittent vertical feed. Balancing parts.-The cutter head 112 and transverse slide 109 are balanced by a weight 118 on the column. Brakes, applications of.-The, clutch spindle 137, Fig. 6. carries an armature 141 which rotates near an electromagnet 142 secured to the clutch case. The magnet is energized when either of the clutch magnets 130, 131 is de-energized and vice versa, to stop rotation of the screw 163 when the clutch is thrown out. Driving machine-spindle ; cutter-spindle feeds. -The cutter 114, Fig. 2, is mounted on a spindle 113 driven through reduction and change gears 256 from an electric motor 117. the spindle being carried bv conical bearings 249 in a sleeve 246 having rack teeth 247 thereon for axial adjustment of the spindle. Copying-mechanism. - The cutter-head 112 carries a bracket 115, Figs. 1 and 2, on which is adjustably mounted a tracer 116 adapted to follow the vertical surface of a pattern supported above the work and control the electric circuits of the magnetic clutches and relay switches. Two tracers are provided, (a) for engraving i.e. copying a relict pattern by means of a series of parallel horizontal or vertical cuts, and (b) for profiling by causing the tracer to follow contour lines on a two or three dimensional pattern. A drumtype. switch having three sets of contacts adjusts the electric circuits for, (1) engraving by horizontal traverse with intermittent vertical feeds, (2) engraving by vertical traverse with horizontal feeds, and (3) for profiling. (a) The engraving tracer 268, Fig. 16, is capable of universal oscillatory and longitudinal movement bv means of a ball-joint 269 and terminates in a hemispherical hardened point 271 which bears in a conical seat 272 on a lever 274 pivoted at 275 and carrying two contact points 277. 278 co-operating with adjustable contacts 279, 280 mounted on the tracer-head and on a lever 282 pivoted at 282a, respectively. A compression spring 285 and a tension spring 284 keep contacts 277, 279 normally closed and a spring 295 normally presses a second contact 293 on the lever 282 against a fixed contact 294. In operation, if the cutter is making horizontal traverses it will be fed into the work until the tracer meets the pattern and is depressed. The lever 274 will then rock and break contacts 277, 279. thus actuating a relay to de-energize the " in " magnetic clutch 230. Horizontal traverse will continue till the tracer meets a projecting perpendicular surface when it will be rocked and will further oscillate the lever 274 to make contacts 278, 280 and energize the reverse clutch 230 to withdraw the cutter. Further side pressure on the tracer will rock the lever 282 to break contacts 293, 294 and stop the horizontal traverse. If the projecting surface is not exactly perpendicular, withdrawal of the cutter and longitudinal movement of the column will alternate. When the projection has been surmounted, the spring 295 returns the lever 282 and horizontal traverse is resumed. (b) The profiling tracer-head 326, Fig. 25, has the tracer 339 mounted therein for oscillating movement only by a ball-joint and the rear end is adapted to rock two levers 328, each lever having two contacts 329, 330, the former being normally closed by springs 337 while the latter are slightly open. The levers and contacts are mounted on a head 327 rotatable by a lever 342 and bevel gearing, the four sets of contacts being connected by brushes 333 to relay magnets controlling the. magnetic clutches for vertical and horizontal motion. Since the two contacts 320 are normally closed, a compound motion such as NE or NW is generated when the lever 342 is set at one of the four positions shown, the contacts 330 controlling the reverse motions. In operation, if it is desired to approach the pattern in a north-westerly direction, the lever 342 is set slightly north of the NW mark so that when the tracer moves from 1 to 2, Fig. 28. and meets the pattern represented by a semi-circular projection x, it will be rocked and open one of the contacts 329 only. thus stopping the west feed. As the north feed continues the west lever 328 will be rocked further to close the reverse or east contact 330. and simultaneously energize a relay magnet 344. Fig. 25, which rocks a lever 346 and cuts out the north feed, thus feeding the tracer from 2 to 3. As the pressure on the tracer is relieved, contact 330 is broken, the relay 344 is de-energized and the north feed again operates. These operations are repeated with small steps until the point 6 is reached, and the north feed alone operates. At a point. such as 7, lateral pressure is removed from the tracer and alternate north-west and north feeds continue till the north-west feed becomes tangential to the pattern, when the head 327 must be rotated to give south-west feed.