Patent GB-687686-A (GB)
Title: Improvements in or relating to a machine tool
IPC: B23Q5/40
Filed: 1951-01-11
Abstract: 687,686. Milling-machines. KEARNEY & TRECKER CORPORATION. Jan. 11, 1951 [Jan. 19, 1950], No. 798/51. Class 83 (iii). [Also in Groups XXIV and XXXVII] A milling or other machine-tool comprises a cutter spindle 16 driven through variable-speed apparatus from a motor 18, a work feeding table 15 driven by a separate motor, overload control mechanism operative. to de-energize the feed motor in accordance with a predetermined degree of overload on the motor 18, and adjustment means operative on the overload mechanism to vary the degree of overload effective to de-energize the feed motor in pre-determined relation to the selected output speed of the variable speed apparatus. The de-energization of the motor 25 is effected whenever the load condition on the motor 18 exceeds the safe torque transmitting capacity of the variablespeed gearing at the selected speed. As shown in Fig. 1, the invention is applied to a milling-machine comprising a column 12 carrying a vertically slideable knee 13 on which a saddle 14 and the table 15 are superimposed for slideable movement in two transverse planes. The movements of the knee, saddle and table are effected at either slow working feed or rapid traverse by a feed motor mounted on the knee. The column 12 also carries the cutter spindle 16 and an over-arm 17 for supporting a cutter arbor. The variable-speed apparatus between the motor 18 and tool spindle 16 comprises a number of gears which are slidable on parallel shafts so as to be brought selectively into mesh and provide any of twenty-four different output speeds under the control of a hand crank 21 and lever 20. Each rotation of the hand crank 20 corresponds to a different speed, and a speed-indicating dial 24 driven by gearing from the crank requires one revolution to cover the complete speed range. The energization of the spindle motor 18 is effected by depressing a start button 181, Fig. 9, and, when this motor has reached full operating speed, a second depression of the button energizes a control circuit for the feed-motor 25 comprising the contact plates 194, 197 of two overload relays 195, 198 in the circuit of the motor 18, the contact plates 204, 207 of two overload relays 205, 208 in the circuit of the motor 25, a solenoid 210 controlling the starting relay 211 of the motor 25, and the contact-plates 221, 224 of two overload relays 192, 191 in the circuit of the motor 18. The relays 195, 198, 205, 208 are actuated to open-position to stop the motor 25 whenever there is a gradually increasing sustained overload on either motor; the relay 191 is actuated to open position to stop the motor 25 on the occurrence of a load on the motor 18 which is equal to the rated capacity of the motor, and the relay 192 is similarly actuated when the load is half the rated capacity of the motor 18. During the first five revolutions of the hand crank 21, i.e. for the five lowest speeds, the lower rated relay 192 is effective since a switch 236 controlling a shunting circuit for this relay is then maintained in open position by a cam 231 on the dial 24; for all higher speeds, only the higher-rated relay 191 is effective since the cam 231 is no longer in a position to open the switch. The solenoid 210 and motor 25 are de-energized whenever these relays are actuated because of an overload condition, and the spindle motor 18 then rotates freely. The knee 13, which is retained in slidable engagement with guides 411, 412, Fig. 13, on the column 12 by fixed gibs 413, 414 and an adjustable gib 417, is movable vertically by the rotation of two elongated nuts 265, 266, Figs. 11 and 13, journalled in the knee for engagement by two vertical screws 260, 261 which are secured at their feet to cups 268 anchored in holes in the machine bed 262. The screws 260, 261 are protected by telescopic tubes 264 anchored between the bed and knee. Gears 295, 296 keyed on the nuts mesh with a third gear 297 to ensure synchronism. Power drive of the knee from the motor 25 is provided through gearing 346, 347, Figs. 13 and 14, safety clutch 349 and a splined shaft 348 having a gear 350 meshing with a gear 303 on the nut 266. Manual operation of the knee is effected from a crank 382, Fig. 13, through shafting 384, 387 and gearing meshing with a gear 302 on the nut 265. In the modification shown in Fig. 10, the nut 430 is non-rotatably screwed to the bed 262 and the screw 435 is screwed at its upper end to a sleeve 437 which is journalled in the knee for drive from the gear 350. The saddle 14 is traversed on the knee by rotating a shaft 330, Fig. 13, having screwthreaded engagement with a nut 343 secured to a bracket 344 depending from the saddle into a well 391 in the knee. Power drive of the shaft 330 from the motor 25 is controlled by a clutch 339 co-operating with two oppositely-driven gears 329, 337 rotatable on the shaft. Manual drive is effected by a hand-wheel 381 on the shaft 330. Dove-tailed guides 393, 394, Fig. 11, at the upper edges of the well 391 co-operate with a depending guide on the saddle, adjustable gibs being provided, and the side edges of the saddle have flanges 407, 408 provided with gibs 409, 410 engaging the knee. The table 15 is traversed on the saddle by a screw-threaded shaft 370 which is journalled beneath the table for engagement by a nut 368 on the saddle. A sleeve 367 keyed on the shaft carries two rotatable gears 365, 366 which are controlled by a clutch 373 and mesh with a gear on a stub shaft 357 rotated from a shaft 352 driven from the gear 329 on the shaft 330. Manual traverse of the table is effected by a hand-wheel 380, Fig. 1, on the shaft 370. The drive from the motor 25 has one branch including variable-speed gearing 320, Fig. 14, providing slow-working feed and a second branch in the form of a shaft 335 controlled by a clutch 317 to provide rapid traverse. Both branches drive the gears 329, 337 on the shaft 330 and, in relatively opposite directions, a gear 338 keyed on the shaft 335 and a gear 334 journalled on this shaft. The knee is moved in desired direction by clutching the gear 346 to one of the gears 334, 338, the saddle by operating the clutch 339 to key one of the driven gears 329, 337 to the shaft 330, and the table 15 by operating the clutch 373 to key one of the gears 365, 366 to the sleeve 367. With the clutch 317 inoperative, the members are moved at a feed rate determined by the gearing 320, but with this clutch engaged an over-running clutch 323 renders the low-speed drive ineffective. The power and manual controls for the knee, saddle and table are so interlocked that, when one of these controls is effective, the other cannot be operated. Fly-wheels, applications.-A uniform rate of spindle rotation is provided by a fly-wheel, Fig. 2 (not shown), secured on the rear end of the spindle, or a fly-wheel may be fitted at the forward end of the spindle, being formed integrally with one of the driving gears on the spindle. Lubricating passages.-For lubricating the screws 260, 261 and the associated nuts and gears, oil may be pumped from a sump in the knee through a tube so as to be led through holes bored in the parts, Fig. 12 (not shown), back to the sump, the telescopic tubes 264 providing a leak-proof enclosure. Specification 499,137 is referred to.