Patent GB-633666-A (GB)
Title: Improved method of and apparatus for blocking lenses
IPC: B24B13/005
Filed: 1947-08-06
Abstract: 633,666. Mounting lenses for grinding. AMERICAN OPTICAL CO. Aug. 6, 1947, No. 21404. Convention date, March 27, 1939. [Class 60] A lens blocking device comprises the combination of a base having an adjustable portion for supporting a lens blank to be blocked, and a head mounted on said base having holding means supported thereby for relative movement toward and away from said adjustable lens blank supporting portion; said adjustable portion being adapted to shift the position of the lens blank supported thereby to given selected locations, and said holding means having depending spring fingers for adjustably and resiliently gripping said blank at spaced portions on the edge thereof, and central pin members adapted to resiliently contact a face of the blank so as to be urged by said blank in a direction longitudinally of said holding means in accordance with the position of the blank, said holding means being adapted to grip a blank of either concave or convex curvature and at any angled position within the limits of its gripping fingers so as to retain the position to which the blank is shifted by said adjustable portion, whereby the said blank may be lifted from said adjustable portion and be retained in said located position. A method of blocking a lens blank comprises resting said blank on supporting means, adjusting said supporting means to given positions to locate the said blank in said respective positions, resiliently gripping and holding said blank at substantially equallyspaced peripheral points in said adjusted position, depositing a given amount of adhesive on a lens block, moving said lens blank, while supported, into alignment with said block and urging said lens blank into engagement with the adhesive while retained in said located position. so that when the said adhesive hardens the said blank will be maintained in the desired located position on said lens block. Apparatus comprises spaced uprights 2, 3 on base 1. The upper end of the upright 2 has a curved seat 6 supporting a member 7 which can thus be adjusted about the centre of curvature of the seat 6, this centre lying substantially on the axis of the upright 2. A member 9 secured to the member 7 extends through a slot in the seat 6 and has a contact face 10 engaged by the end of an adjustable screw 12; a stop 13 is provided. The lower end of the member 9 carries a pointer 14 extending through a slot in the upright and co-operating with a scale 16 on the base. A spring 18 urges the member 9 in a direction to maintain the contact face in engagement with the end of the screw 12; a spring 21 maintains the member 7 in contact with the seat 6. A plate 28 secured to the member 7 has a shouldered recess 30 in its upper face in which is mounted a rotatable member 31 having openings 33 to receive balls 34 ; the disc 31 has a central opening fitted with a translucent member 32 ; a line on the disc 31 cooperates with a degree scale. A semi-finished lens block 37 is placed on the balls 34; the desired amount of prism is then introduced by adjusting the screw 12 until the desired reading of the pointer 14 on the scale 16 is obtained, e.g. graduation " 3 " of the scale 16 indicates " 3 prism diopters."-If the finished lens is to have a cylinder axis and a prism axis not coincident with each other, the disc 31 is turned until the desired reading of the line with the scale is obtained, e.g. if the prism axis is to be 30 degrees away from the cylinder axis, the cylinder axis is lined up with the 90 degrees- 90 degrees line of the scale, and the disc 31 is then rotated to bring the location line into alignment with the 30 degree line of the scale. A sleeve 45 is vertically movable in housing 40 on a bracket 41 and clamped in desired position by a screw 76. An assemblage comprising members 38 for contacting the upper face of the lens block and members 58 for gripping the periphery of the lens is carried by the sleeve 45 which is downwardly urged by a spring 39. The members 38 are individually loaded by springs 42. The members 58 are mounted on spring fingers 54 so as normally to be urged inwards; they are moved outwardly by a cam 59 which can be rotated by a handle 61. The lens blank having been correctly positioned by the adjustments described in the previous paragraph, the screw 76 is loosened and the sleeve 45 is lowered so as to bring the members 38, 58 into engagement with the lens blank; clamp nuts 53 are then tightened so that the lens blank is gripped. Sighting means are provided, comprising a lamp in the upright, the light shining through the translucent member 32, the lens blank, a transparent member 74 having cross-hairs thereon, a restricted opening 69 in a washer 68 and a restricted opening 70 in a cap 67. The other upright 3 has a tapered support 80 on which is fitted an adapter 81 having a recessed end receiving the shank 83 of the lens block 82 ; the shank 83 has a circumferential taper 84 engaged by set-screws 85. The bracket 41 has an extension to which is secured pitch kettle 87 having electrical heating coils in the wall portion, and having spaced shelves 114, 115 on which the lens block 82 and blanks 87 may be placed for preheating. The kettle has an outlet valve 90 which can be opened by a hand wheel 100 to deposit pitch on the lens block 82 ; a ring 119, Fig. VI, is placed on the block 82 to retain molten pitch on the effective attaching surface of the block 82. In use, the lens blank is located and gripped, as described above; the screw 76 is then loosened, and the sleeve 45 raised and again clamped by the screw 76 whereby the gripped lens blank is lifted clear of the upright 2. The hand wheel 100 is then turned to operate the valve to deliver the desired amount of molten pitch on to the lens block, as described above. A hand wheel 106 is then turned to move a latch member out of a locking slot; the bracket 41 is then swung to bring the lens blank 37 into alignment with the lens block 82 ; the latch member engaging a second locking slot. The screw 76 is loosened, and the lens blank lowered into contact with the molten pitch. When the pitch has cooled, the blank gripping means are rendered inoperative. In a modification, the bracket cannot be swung until the lens has been lifted clear of the locating means on the first upright.