Patent GB-691937-A (GB)
Title: Improvements in or relating to the machining of turbine or axial compressor blades
Inventor: LEGG GEORGE CHARLES JAMES
IPC: B24B17/02
Filed: 1950-08-28
Abstract: 691,937. Copy-milling; chucks. NAPIER & SON, Ltd., D. Nov. 20, 1951 [Aug. 28, 1950], No. 21190/50. Class 83 (iii). [Also in Group XXIII] In a method of machining twisted turbine or axial-flow compressor blades the blade 6 is given not only a progressive rotary movement about its axis, and a longitudinal reciprocating movement relative to a rod 8, but also a further rotary oscillating movement about the same axis to produce a helical motion corresponding to the twist of the blade. In the preferred embodiment, a former and the blade are mounted on a common support 3 pivotally mounted on anti-friction bearings 5b on a carriage 2a arranged to reciprocate on the base 1 of the apparatus. The blade 6 is mounted between an adjustable centre 3e and a collet chuck 13 arranged to be actuated by a screw at one end of a clamping- rod 28 so that its jaws co-operate with a tapered bore in a shaft 12 having two conical facings to form a double-thrust bearing. The former 7 is bolted to a flange 12b rigidly connected to the shaft 12 and a flange 11b rigidly connected to a shaft 11 mounted in anti-friction bearings. Oscillating motion about the axis of these shafts is imparted to the blade and former by a sleeve 22 having a helical slot 23 co-operating with a pin or roller 24 rigidly secured to the base of the apparatus. To enable the rotary feed movement in addition to the oscillating motion to be imparted to the blade and former, the sleeve 22 is connected to the shaft 11 through a casing 15 mounted on bearing bushes 16 and supporting a worm 19 in engagement with a worm-wheel 14 clamped to the shaft by nuts 17. The oscillation of the sleeve is thus transmitted to the worm through the casing and hence to the shaft 11 while a progressive rotary movement of the latter relative to the sleeve is obtained, by rotating the worm with a variable-speed D.C. motor 21. The sleeve is clamped against the casing 15 by the rod 28 which has a collar 27 to hold an end cover 26 in position. A follower wheel 9 may be adjusted towards and away from the former by a fine-pitch screw 32, the position of the follower being indicated by a gauge 33 bearing against the screw. The former is held against the follower by a spring- loaded plunger (not shown) interposed between the support 3 and the base 1. When a number of cuts have to be taken, the follower is first adjusted to its correct final position coaxial with the grinding-wheel 8 and the gauge 33 set to zero. The follower is then adjusted to hold the former and blade away from their true positions, the displacement shown by the gauge 33 being used to subdivide the whole grinding operation into as many steps as desired. A milling cutter, belt-driven from an electric motor 36, and mounted in an adjustable support 35, is employed. An idle pulley 37 enables the belt tension to be adjusted. The apparatus may be used for shaping a blade former from a master blade which is mounted in place of the blade 6, the unshaped former replacing the former 7. The follower wheel is mounted on a swivel head 45 carried by an adjustable support 44 and the normal follower is replaced by a milling cutter driven through a flexible shaft and a belt drive from an electric motor.