716,915. Rounding the edges of blades. BRISTOL AEROPLANE CO., Ltd. April 27, 1953 [May 5, 1952], No. 11334/52. Class 60 A method of abrading the long edges of a blade-like element to round them comprises inserting the element lengthwise between a pair of taut unsupported lengths of flexible abrading band, belt or the 'like arranged with their abrading surfaces facing one another substantially parallel and spaced apart by less than the minimum width of the element, and then rotating or oscillating the element substantially about its long axis. The blade-like elements may be flat or transversely curved, e.g. turbine and compressor blades, the leading and trailing edges of which are to be polished. To facilitate insertion of the blade, the band lengths are preferably spaced apart by more than the overall thickness of the blade. The band lengths may be portions of a single endless .band or of a pair of endless bands, the band or bands being driven to move the lengths across the long edges of the blade while it is rotated. The blade may be rotated successively in opposite directions. The width of the band or bands may be less than the length of the blade, and the latter reciprocated substantially lengthwise while it is rotated; the blade is rotated in opposite directions during successive strokes of its reciprocating movement. An endless flexible felt belt 42, impregnated with abrasive material passes around pulleys 13, 26, 31, 16, 31, 26. The pulley 13 is on one end of the shaft 14 of an electric motor 11 mounted'within the base 10. Mounted on top of the base 10 is bearing housing 15 for the shaft 17 of the pulley 16, the shaft 17 being eccentrically adjustable in the housing 15 to facilitate the fitting and removal of the belt. Upwardly inclined arms 20, 21 are swingably mounted on the bearing housing.15 each by means of a single bolt 30 ; the arms have longitudinal slots 23 and are bridged at their free ends by horizontal strap 24 having longitudinal slots 25 towards its ends. A pulley 26 is carried at the free end of each arm 20, 21, its shaft 27 passing through the slots 23, 25 thereby fixing the strap 24 to the arms 20, 21, the slots allowing adjustment as desired. A belt tensioning jockey unit 29 having a jockey pulley 31 is mounted in the slot 23 of each arm 20, 21 so that the pulleys 31 lie between the arms. Each pulley 31 is carried on a spindle 32 having a ball end 33 mounted in a spherical housing 34 formed in a two part block 35 one part of which is carried at. the end of an arm 36 hinged at its other end by a bolt 37 to a plate 38 having a T-slot 39. The two parts of the block are clamped together by a screw 115 to grip the ball end, and the screw may be slackened to loosen the ball end 33 so that the . spindle may be adjusted. The arm 36 carries a lever 40 and a coiled tension spring 41 is connectedbetween the free end of the lever 40 and a coiled tension spring 41 is connected between the free end of the lever 40 and the plate 38 to urge the pulley 31 away from the arm on which it is carried. The units 29 are attached to their respective arm 20 or 21 by a bolt passing through the T-slot 39 in the unit and the slot 23 in the arm, whereby the position of each'pulley 31 is adjustable. The run of the belt 42 follows a generally double V-shaped path, and the runs forming the inner V-shape pass over the jockey pulleys 31 which are positioned one above the other so that a pair of unsupported lengths 43 of the belt run substantially parallel with their abrading surfaces facing each other ; the pulleys 31 being spring urged away from their respective arms tauten the belt and the pulleys 31 and arms 20, 21 may be adjusted to vary the space between the lengths 43. If the blade is tapered, the spindles 32 are mutually inclined, after slacking off the screws 115 to loosen the ball end 33 of each spindle in its housing 34, so that the lengths 43 of the bell converge transversely to correspond with the blade taper. A work-head is adjustably mounted in elongated slots 82 at the end of a double arm 75 hinged at its lower end to an arm 76 projecting from the base 10. The arm 75 is oscillated by a rod 71 having a crank pin 70 adjustable in a slot of a thrower 58 on a shaft 57 which is driven from the motor 11 by pulley 12 belt 52, pulley 51, shaft 54, worm 55 and worm wheel 56. The shaft 54 rotates, through a flexible shaft 81, a work-holder 80 in the workhead. The rod 71 is releasably and adjustably connected to the arm 75 in order that. the position of the work-head in relation to the belt 42 may be varied as required and also in order that the arm 75 may be swung back for insertion and removal of the work-piece from the holder. The connection comprises a split sleeve 106 locked to the rod 71 by a screw 107 ; a block 10 attached to one limb of the arm 75 by a pivot 109 is recessed so as to be a sliding fit over a reduced portion 110 of the sleeve 106. A spring-loaded plunger 111 mounted on the block 10 engages a slot 112 in the sleeve 106 ; the arm 75 can thus be swung back by lifting the plunger 111 to free the block 108 from the sleeve 106. For adjustment, the screw 107 is loosened and the sleeve 106 moved to the desired position. The work-holder 80 is automatically reversed, being driven, by the flexible shaft 81, through a bevel reversing gear operated by a lever 95 pivoted to the work-head casing, the outer end of the lever 95 carrying a rod 98 slidable in a block 99 carried on the centre of the strap 24. The block 99 has a pair of screws 100 adjustable to vary the sliding friction of the rod 98 in the block 99. A stop member is pivoted to the top of the work-head and can be swung to an operative position in which the lever 95 is held in a neutral position. The shaft 58 of the thrower 57 carries at its opposite end a finger 59 arranged to engage a number of spaced pins 60 on a freely rotatable timing disc 61 so as to turn the disc. The disc carries a cam 62 on its peripheral edge adapted to engage a roller 63 on an arm 64 associated with a micro switch 66 which acts through a relay to stop the machine. The timing of the operation depends on the length of the finger 59 and the number of pins 60.. Metal guards 113 are provided over the belt 42 and timing gear unit.