Patent GB-630668-A (GB)
Title: Improvements in or relating to a universal screw propeller generator, to apparatus for and a process of generating a desired shape employing said apparatus
IPC: B23D3/04
Filed: 1945-01-22
Abstract: 630,668. Generating screw-propellers &c. ZIMMERMANN, M. K. VON. Jan. 22, 1945, No. 1710. Convention date, Jan. 29, 1944. [Classes 83 (ii) and 83 (iii)] [Also in Groups XXIV, XXIX and XXXVII] A machine for reproducing a desired shape is described with reference to machining screw-propellers. The propeller is mounted on a rotary table that oscillates a blade beneath a pair of opposed tools cutting alternately and carried by a ram from a slide system controlled automatically to raise and lower the tool in synchronism with the movement of the blade to reproduce the contour required as determined by a series of cams, one for each cut across the blade, indexed into position prior to each cut, the ram receiving an intermittent motion to displace the cutter lengthwise of the blade in preparation for a new cut. The machine has means for moving the tool-head to maintain the proper cutting-angle as the cutting-direction varies. Movement correcting mechanism automatically provides compensation and controls as a function of the movements of various elements of the machine and cutting-speed control means maintain constant lineal cutting-speed. The machine also cuts its own cams according to mathematical data supplied by the designer. The table is indexed from blade to blade and the propeller is reversed on the table for cutting the backs of the blades. The propeller S, Fig. 1, is placed with the aft or operative face upwards and bolted through its boss on to the rotary table B supported on a saddle C on guides 6a . . . 6d on the frame to permit the centre of rotation to be adjusted forwards or back according to whether a right or left hand propeller is being machined. Supports 3a for the tips of the blades are bolted to the table. The adjustment is effected by a hand crank 7 geared to screws 8a, 8b. The toolhead K is carried by a ram I adjustable step-bystep between cuts in a guideway H pivotally mounted on a slide 102a and supported by an arcuate trackway 113 on the slide 102b, graduations 113d co-operating with an index mark facilitating the initial setting which is effected manually by a hand wheel 115 on a screw 114 engaging a nut 110c, Fig. 11, pivotally mounted in a die block 110b slidable in a slot 110a in the ram housing. In the case of a blade having constant rake no further adjustment is needed, but for blades having variable rake this may be changed automatically between cuts from the mean position thus set by hand. The housing is locked after adjustment by three T-headed bolts 141 provided with pinion nuts engaged by a rack 144 operated by an air cylinder 145. After unclamping, a further cylinder 139 closes a friction clutch 135, Fig. 12, and then a cylinder 138 by a rack, and toothed segment 137 rotates the screw 114 sufficiently to move the nut 110c down out of engagement with a stop-pin 124a. At the same time the clutch drum 134 raises a weight 147 by a rope 146. A cylinder 132 then operates through a pawl 131a to rotate by a ratchet wheel 130 a drum carrying the series of stop-pins 124a, one for each cut to be made, to bring the next pin into position, after which the clutch opens and the weight 147 returns the screw 114 to bring the nut into contact with this pin and finally the pinion nuts relock the housing. The movement of the ram 111, in its housing 110, Figs. 7 and 16, is imparted by a screw 150 rigidly and non-rotatably supported in the ram at its ends, and engaging a nut 151 rotatably mounted in the housing. Teeth 151a on the nut are geared to teeth 153a on a sleeve carrying also pinion teeth 153b and a ratchet-wheel. Three pawls engage this wheel and are controlled by a hand-operated cam so that they may be raised clear of the ratchet wheel when required. For the step-by-step movement between successive cuts the pawls are operative and a cylinder 161 operates a rack 164, through the means shown, rotating a . pinion 165 driving, through bevel-gearing, the shaft on which the ratchet-wheel sleeve is keyed. Rapid feed for adjustment or quick return is obtained from a motor 160 geared to the pinion 153b, the pawls being then in inoperative position. The ram 111 carries a double cutter-head K, Fig. 29, tools 194, 195 cutting alternately on successive cuts as the work-table oscillates. The Figure shows a toolhead for machining a left-hand propeller, a special head being provided for one of righthand, the difference being in the range of movement and in the final direction of drive. The tools are carried by slides 196, 198 operated by cylinders 200, 201, and locked by bars 204 operated by cylinders 202, 203. The cutting- angle is controlled by rocking the head K in arcuate guides by a double arcuate rack 190 driven simultaneously on its convex and concave sides by pinions 191, 192, both driven from a shaft 180 driven through worm and spur gearing from a shaft coaxial with the pivot of the ram housing. The drive is derived from the speed-changing screw 304m, Fig. 7, of the variable-speed gearing connecting the table rotation and tool traverse by a system of geared shafts 170, 171, and 172, the shaft 172 being splined in gearing 173 driving a shaft 175 that drives the coaxial shaft. The drive is thus not interfered with by the various adjustments and movements of the slides. The depth of cut and proper initial position of the tool-head is controlled by a hand wheel 186 through a screw 185. A motor 300, Figs. 1, 6 and 34, supplies the main drive to the machine, a smaller motor 301 being used during setting up and during cutting cams. The motor 300 transmits through change gears 308a to a shaft 302 also geared by change gears 308 f and a chain to the motor 301 some of the gears being removed to cut out the motor idle for the time being. Gears 310a transmit to the input shaft 304a of a variable-speed belt-gear 304h the cones of which are operated by levers 304k from the screw 304m. The output shaft 304f drives the sun-wheel of a differential gear 305, the planet carrier of which drives the shaft 305c, the planet-wheels engaging also internal teeth on a drum 305a geared through a train 311c to the shaft 302. Further change gearing 312a, 314b, Fig. 38, connects the shaft 302 with a shaft 313 and through a clutch 317b with the shaft 319, couplings 320a, 320b, bevel-gears 321 and shaft 109. The shaft 109 is geared through shafts 108a, b, to vertical shafts 107a, b, Fig. 7, to rotate worms 104b and traverse the slides 102a, b, on the columns 100a, b, cross-braced at 102, Fig. 2. The shaft 109 is also connected to the shaft 305c through shaft 322 and couplings 323a, b. The tool-slides are driven through the shaft 319 for constant pitch machining and through the shaft 322 for variable pitch and for machining the backs of the blades. In the former case the gear 310c is removed and in the latter the clutch 317b is opened. The table is driven in geared relation to the tool slides by bevel-gearing 326, Fig. 6, from the main shaft 302, reversing-gears 327 and bevel-gears and shafts 328, 330 and 332, the last driving an internal gear carried by the table. When cutting the aft face of a variable-pitch propeller the change-gearing 312a, 314b is adjusted to the mean-pitch as closely as possible and the departure from this is imparted by cam-mechanism operating the speed-changing screw 304m. The cams are carried in a frame traversed under a follower to apply the correcting motion, the cams being to a reduced scale, such as one-half, so that the cam frame is traversed at half the speed and for half the distance as the projection of the cut on the table. The drive for this motion is taken from the internal gear-ring on the table by a pinion on the shaft 335, Fig. 6, and is transmitted by shafts 337, 338 to a transformer which transforms the rotary table speed into the correct lineal cutting speed for the particular mean pitch selected at each successive position of the tool as the ram indexes outwards from the hub. The reversing-gear 327 is of the threewheel tumbler type and is hand set according to the hand of the blade. There is also a neutral position used during setting up if it be desired to traverse the tool-slides without rotation of the table. The means for maintaining constant lineal cutting speed comprises a controller drum R, Fig. 45, having a number of sets of annularlyarranged contact buttons 341a insulated from the drum and connected to the ends of a bank of resistances forming the field rheostat of the motor 300. The correct contact button for the particular stage of the cutting is selected by a contact on an arm 343 carried by a splined shaft 344 sliding in a worm 345 on a shaft 347, Fig. 6, geared to the variable-speed control screw 304m. A coupling in the shaft 347 enables initial adjustment of the position of the arm 343 to be made. From time to time as the tool is moved radially outwards for fresh cuts the shaft 344 is moved axially to position the arm to traverse the next row of contact buttons; the movement being effected by a cylinder 349 actuating a pawl 351 meshing with a rack connected to the shaft. The cylinder valve is operated electrically by a switch actuated by spaced tappets on a part 570, Fig. 80, of the motion correcting transformer. A tappet switch associated with the cams closes at the end of each cut to energize a solenoid 370, Fig. 48, operating a rack 368 against a spring to rotate a combined pinion and ratchet wheel 366 engaging pawls 365a on an insulating disc 363 carrying a pair of contacts 361b wiping over a series of eight contact studs 360c in a fixed insulating disc 362. At the end of a forward cut the contacts move to the next pair of studs which are wired to cause dynamic braking to stop the motor quickly. After a pause sufficient to permit the various intermittent movements to take place the solenoid is again actuated through a delayed action relay to move the contacts to the next pair of studs causing rotation of the motor in the reverse direction