Patent GB-655317-A (GB)
Title: Propeller milling machine for simultaneous machining of two or more screw propellers
IPC: B24B19/14
Filed: 1947-12-15
Abstract: 655,317. Propeller-milling machines. TVEITAN, A., and MYRHOLT, L. Dec. 15, 1947, No. 32937. [A Specification was laid open to inspection under Sect. 91 of the Acts, April 12, 1948.] [Class 83 (iii)] A propeller milling machine operating on two or more propellers 3 simultaneously and cuting along meridional sections, t.e. intersections of the propeller surface with planes having the propeller axis as their common intersection line, has one or more pairs of propeller-carrying slides 2 arranged to be traversed to and from each other by screw means and corresponding milling cutters mounted in pairs, each cutter of the pairs being mounted on its own side of one or more slides 8 movable by screw means in a direction perpendicular to the direction of movement of the propeller slides. The machine may be modified to cut cylinder sections, i.e. intersections of the propeller surface with cylinder surfaces centred on the propeller axis, or normal sections, i.e. where the intersecting planes are perpendicular to the propeller axis, or to machine the axially-projected blade outline of the propellers or to operate simultaneously on two or more blades of the same propeller or series of propellers. General arrangement.-A pair of slides 2 each carrying a propeller 3 are traversed in opposite directions on a beam 6 by a lead screw 4 having oppositelythreaded halves and a cutter slide 8 is traversed perpendicularly to the slides 2 by a lead screw 13. On each side of the slide a motor 10 is adjustable vertically and drives a vertical shaft mounted in an arm 11 and carrying an end-milling cutter 12. A drawing of the propeller sections is carried by a table 21 which is fed by a lead screw spindle 23 driven by hand or by a motor 24 and above the table a threaded sleeve carries a transparent disc 19 marked with a representation of the cutter to the scale of the drawing and engages a lead screw spindle 17 rotated by hand or by a motor 20. The disc may be viewed by means of a mirror and an optical viewing device may be kept trained on the mirror by a drive from the disc spindle 17. Each propeller is mounted on a spindle 30 rotatable in the slide by means of a worm wheel 31 engaging a worm spindle 32 having oppositely-threaded halves. Operation.-When cutting meridional sections, the speed of the disc motor is regulated by a hand controller in relation to the speed of the table motor 24 so that the cutter circle on the disc 19 is maintained tangential to the drawing section. The cutter slide spindle 13 is interconnected with the disc spindle 17 by means of gearing 14, a shaft 16 and gearing 15 and the table spindle 23 is interconnected with the propeller slide spindle 4 by gearing 27, a shaft 29 and gearing 28. The spindle 4 is also interconnected with the worm spindle 32 by gears 33, 34, the former fixed on the spindle 4 and the latter secured to the worm spindle 32, on which it is rotatably mounted, by a spring-loaded pin engaging holes in a bevelgear 36 fixed to the worm spindle. The ratio of the gears 33, 34 is such that the worm wheels 31 move along the worm spindle 32 without rotating the propeller spindle, thus giving traverse without rotation. After each cut from hub to tip, the propellers are turned, through the angle required to bring the plane of the next meridian section horizontal, by rotating the worm spindle 32 by a handle on the gear 36. When cutting cylinder sections, the propellers are rotated without traverse from the table spindle 23 through the gears 27, 28, a gear 37 rotatable on the spindle 4 and a gear 38 rotatable on the worm spindle 32 but, in this case, secured to it by a conical fixing pin engaging a disc 40 fixed to the spindle. The spindle 4 is secured against rotation by engaging a fixing pin on the gear 33 with a disc 35 fixed to the frame. After each cut across the width of the blade, the propeller slides are traversed to bring the next cylinder section into cutting position by a handle on the gear 33 on the spindle 4. For cutting these sections, the pattern drawing is modified to take account of the diameter of the cutter. Axially-projected blade outlines and normal sections are cut by rotating and, at the same time, traversing the propellers. For outline cutting, a side-cutting tool with its axis parallel to the propeller axis is used. The disc spindle 17 is connected to the worm spindle 32 by a gear 47, engaged with a disc 51 on the spindle 17 by a conical pin, and gears 48, 49 to the bevel gear 36 fixed on the spindle 32, the propeller slide spindle 4 is rotated by the table spindle 23 and the cutter slide spindle 13 is disengaged from its drive. By regulating the motors 20 and 24, the disc 19 is made to follow the curve on the drawing and the propellers are rotated on their axes and traversed in correspondence. For moving from one normal section to the next, the cutter slide may be displaced by turning its spindle by a wheel 61, Fig. 6, and secured by engaging a fixing pin on a disc 62 on the beam 7. Alternatively, for cutting normal sections, the propeller axes may be arranged vertically and the gearing arranged as for meridional sections, the cutters being adjusted vertically to cut each new section. For simultaneously machining two blades of one propeller 52, a propeller spindle 57 is journalled and axially displaceable in a block 59 joining the beams 6 and 7 and is also journalled in arms 60 by which it is connected to the cutter slide 8. The propeller spindle is connected by gearing 56, 55 and 53 to the worm spindle 32 and the cutters 58 are mounted on the propeller slides 2. The arms 60 are rotatable on circular portions of the beam 7 and slide 8 so that they may be swung out of the way when not required. For simultaneously machining all the blades of a fourblade propeller, two additional cutter-carrying slides may be mounted to slide on guideways perpendicular to the slides 2, or, similarly, for a three-bladed propeller, three slides movable at 120 degrees to each other may be used. For cutting helical lines on the propeller without the use of a drawing, the cutter slide feed nuts may be disengaged from their lead screw and the slide fed by a pitch regulating bar 63 slidable through a trunnion 64 on the slide and connected at its ends to, respectively, a bar 91 adjustable to set the pitch angle and a bar 65 which is fed by a nut 66 engaging screw threads on the shaft 16. The worm spindle 32, in this case is rotated by the disc spindle 17. To prevent operation of the motors 20, 24 when the gear fixing pins are fitted in an undesired combination, electrical contacts 43 controlling relays in the motor circuits are fitted in the covers 42, Fig. 5, for the gear wheels. The fixing pins have a bent arm 44 which fits in a deep hole for the locking position and in a shallow hole for the unlocked position ; in the latter position, the pin presses by means of a small wheel 45 against a disc 41 and closes the contact 43. The gears 28, 37 on the propeller slide spindle 4 must not be locked to each other at the same time as the pin on the engaging gear 38 locks it to the worm spindle 32 and the contacts for each of the gears 37, 38 are connected in parallel so that the circuit is closed with only one pin in position. The gear 33 on the propeller slide spindle should not be secured to the fixed disc 35 when either the gears 28, 37 at the other end of the spindle are locked to each other or when the worm spindle 32 is being driven from the spindle 4 through either of the gears 34, 38, and similar contacts on the gears 33, 34 are connected in series in diagonally-opposite fashion with the first contacts. To prevent operation of the machine with the gear wheels uncovered, the covers also have a contact which is opened when the cover is opened. Preventing backlash.-To take up backlash in the feed-nuts, they comprise two sleeves 5, Fig. 4, which can be screwed towards each other on the spindle and then each secured against rotation by a bolt 90 passed through one of a set of holes in the sleeve flange into a coinciding hole in a set of holes in the slide, the latter set being one more or less in number than those in the flange. Backlash of the gears on the spindles 4, 13 and 32 may be prevented by auxiliary electric motors which tend to turn the spindles in the opposite direction to the main drive but are over-run by the main drive and backlash of the worm wheels on the propeller spindles may be prevented by drums, wires and weights. Varying scale of reproduction.-To vary the scale of reproduction, pairs of different-sized gears, one fixed to the spindle and the other rotatable on it but capable of being locked together or two gears rotatable on the spindle at one end and capable of being locked separately to an intermediate disc secured to the spindle, may be fitted in place of the single gear pairs 14-15, 27-28. Also the gear pairs 33-34 and 37-38 may have different ratios or the drive to the spindle 4 may be taken the roundabout way through the worm spindle 32. Also, by driving the propeller slide spindle 4 or the worm spindle 32 from the table spindle 23 and the cutter slide spindle 13 from the disc spindle 17 through the regulating bar 63, the latter may be adjusted so as to vary the scale of reproduction from a drawing.