GB402768A - Improvements in or relating to machines for milling and/or grinding propeller blades - Google Patents

Abstract

402,768. Grinding screw-propellers. CHURCHILL & CO., Ltd., C., 27, Walnut Street, Kennington, London, and CLEMENSON, F. C., Pioneer Works, Parkinson Lane, Halifax, Yorkshire. June 1, 1932, No. 15491. [Class 60.] Helical surfaces, grinding and treating.-In a machine for grinding screw propeller blades the propeller 3 is carried on a shaft 2 which has a combined axial and twisting movement so as to carry a blade 31 in a helical path past a pivotally mounted milling-cutter or grinding- wheel 9. The helical motion is derived from the combined action of a reciprocating rack 4 engaging a quadrant 41 on the propeller shaft and an angularlyarranged slotted pitchbar 5 moved in a direction perpendicular to the propeller axis and co-acting with a block 6 pivoted to a boss 7 loosely mounted on the propeller shaft. An indexing-plunger 8 allows any of the propeller blades to be brought into operative position. The grinding-wheel 9 is mounted on the spindle of a motor 11 carried by a tubular arm 10 which is mounted on trunnions 12 in a drum 13 rotatable in bearings 14 on a slide 15 movable by a feed-screw 16. The feed-screw is actuated through gears 17, shaft 18, ratchet mechanism not shown, and gear 19 reciprocated with a slide 45. As the slide 15 is traversed the drum is rotated in its bearings by means of an adjustably fixed slide bar 26 engaging an arm 28 secured to the drum. This causes the tool to be moved in a circular path for the purpose of compensating for the interference of the cutter circle. In order to shape the backs of these blades a thickness templet 42 is employed. The underside of arm 10 has gear teeth 31 engaging a rack connected through a circular rack 32, gearing 34, rack 37, gears 38 and splined shaft 39 to the boss of an arm 40 carrying a roller 41 engaging the templet which m ay either be of hardwood or built up of a series of sheet metal templets on edge. The templet is carried on a slide 21 which is operated by a screw driven from a shaft 21<1> in unison with the feed screw 16. The slide 45 carrying the pitch member 5 and a slide 43 carrying slide 21 are reciprocated from crank discs 47, 46 respectively, the crank discs being driven from an electric motor 49 through reduction gearing 48. The back shaping mechanism controlled by the templet 42 is disconnected while the front of the blades is cut. For cutting blades which have a variable pitch from tip to root, the shaft 211 is connected through gears 23 to a screw 24 operating a block 25 which varies the inclination of the pitch bar during the feed of the tool along the length of the blade. For cutting raked propellers the pivot of the pitch bar 5 is carried on a supplementary slide which is moved step by step in the direction of the movement of slide 45. If a blade having a curved centre line is to be cut the supplementary slide is moved in gradually increasing steps by cam or similar mechanism. For shaping propellers having a variable pitch across the blade face the screw 24 which modifies the inclination of the pitch bar may be moved axially by means of a cam which engages the end of the screw as the slide 45 reciprocates.