GB625771A - Improvements in or relating to grinding, milling or the machines - Google Patents

Abstract

625,771. Grinding and polishing. BRISTOL AEROPLANE CO., Ltd., WHITEHEAD, F. W., and BEDFORD, W. H. March 19, 1947, No. 7628. [Class 60] [Also in Group XXII] In a machine for milling or grinding the concave surface of gas turbine or compressor blades, the tool 29 is reciprocated along its axis of rotation to perform a cutting operation and the work-holder 37 is rotatable about twc axes at right angles to each other, movement of the work-holder about one axis causing a former 53 to pivot the work-holder about the other axis by an amount determined by the first movement. The blades Figs. 1 and 2, are tapered in thickness and are twisted round the longitudinal axis b; the lines d inclined to the axis b in Fig. 2 are " co-incident " lines representing the lines of contact of the tool with the blade. The tool head, Fig. 3, comprises a grinding wheel or milling cutter 29 having a length equal to or slightly greater than that of the vane surface of the blade being manufactured and driven through a gearbox 27 from a motor 28. The cutter shaft 31 extends through the cutter and is supported by an arm 32 on a rod 33. Slides 25, 80 provide for axial and lateral feed of the cutter under the control of handwheels 24, 81 respectively. The blade 67, Fig. 6, of which the convex surface has been formed in another machine, is supported by a tapered block 69 attached to a channel-section member 68 fitted in the work-holder 37. The bottom of the channel-section is cut away to accommodate an anvil 74, which is adjustable by a fork 75 and screw 76 and a block 72 for a clamp 77 holding the root of the blade on the anvil. The work-holder is pivoted by a vertical pin 48, Fig. 7, in a platform 36 which is journalled in a bracket 35 for rotation about a horizontal axis by a handwheel 39, Fig. 3. The bracket 35 has bearing pads engaged by the platform 36 and work-holder 37 and also adjustable stops to limit rotation about a horizontal axis. The work-holder 37 has a radial arm 51 carrying a roller 52 which engages the former 53 constituted by a cam surface removably mounted on a pedestal 54, the roller and cam surface being held in contact by a weight 58 and rope 55 attached to the arm 51. In operation, the cutter is first advanced along its axis to cut a concave groove in the blade, the holder being locked by pin 61 engaging a slot 62. The cutter is inclined to the axis b of the blade, Fig. 7, so that it cuts along one of the co-incident lines d, Fig. 1. The pin 61 is then withdrawn by a lever 63 and the handwheel 39 is rotated so that the platform 36 is rotated about the horizontal axis e and, influenced by the cam and roller, the work-holder is rotated about the axis f. Owing to the inclination of the cutter, the root-end of the vane is not disposed normally to the axis b and may be furthered machined to rectify this. The cutter is of conical shape, the larger end conforming to the form of the root end of the vane the cutting face of the cutter may be straight, curved, or part curved and part straight, the co-incident lines produced on the blade being correspondingly straight or curved. The Provisional Specification describes also a similar machine but having a fixed work-holder and a cutter tapering towards the end engaging the root of the blade.