Patent GB-190428823-A (GB)
Title: Improvements in Bi-focal Lenses and their Manufacture, and in Apparatus to be employed in the said Manufacture.
Inventor: BENTZON MALCOLM
Filed: 1904-12-29
Granted: 1906-01-29
Abstract: 28,823. Bentzon, M., and Emerson, A. H. Dec. 29. Lenses.-Relates to solid bi-focal lenses, particularly for spectacles and eyeglasses, and to apparatus for making them from single pieces of glass &c. The lenses may be constructed in such a way, as shown in Fig. 2, that there is no ridge or step between the parts of different curvature. Fig. 1 shows a lens with such a ridge. The two curvatures may be formed at one operation by a machine carrying two or more tools as shown in Fig. 8, or glass on which one of the curvatures has already been produced may be operated on by a machine carrying a single tool as shown in Fig. 3. Two single-tool machines may be used togecher. The glass-carriers are supported on a table 3* carried by a rotating spindle 3, Fig. 3, mounted in bearings on an adjustable slide 2, while the toolcarrying spindle 4 is rotatable in bearings on a carrier head 5 adjustably clamped to an arm 6 pivoted to a lever 7 which carries a block 7* adjusted by a screw 8 and a spring 23, to enable the position and inclination of the tool spindle to be adjusted. The pressure of the tool on the work is adjusted by weights 6* on the arm 6. A support 8* is provided for the arm 6 when turned back. The tool @ is shown attached to the spindle 4 by a ball 11 engaging a spring 14, and a tongue 12 engaging slots in the tool and in a collar 13. The tools may rotate in the reverse direction to or in the same direction as the lens-holder, or the lens-holder may be stationary and the tools made to revolve as well as rotate. Approximately the desired curvature is produced by steel &c. roughgrinding tools, after which smooth-grinding tools of softer metals, such as brass, and then polishing- tools are used. The polishing-tools may be covered with felt which has been boiled in pitch. To enable the curvature produced to be independent of the curve of the grinding-surface of the tool, tools with hollowed or recessed underside are used, so that their grinding-surface is greatest at the parts which tend to grind away quickest. The curvature produced depends on the relative surface velocities of the lenses and tools, and the relation between the two is adjusted according to the curvature required. When two lenses are operated on together, as shown in Fig. 3, their adjacent edges may be cut flat to bring them close together, and filling-pieces may be placed in the gaps between them, to form a complete circle of glass. Fig. 8 shows two tools arranged to produce the two curvatures simultaneously on a piece of glass which may afterwards be cut up and treated as desired. The tools have square holes engaged by square parts 42 on tool-spindles 25, 33 supported as shown and rotated and revolved at the desired speeds by pulleys 31, 32, 37, &c. through the gearing shown. The supporting-arms 26, 35 can be replaced by longer or shorter ones according to the size of the piece of glass operated on and the relative areas of the two curved surfaces. A single tool is used on the inner surface, while two or more tools may be used simultaneously on the outer surface. Two or more glass-holders 17 arranged at an angle to one another as shown in Figs. 3 and 13 may be secured to a block 16 with inclined seats by screws 19 as shown, and the block may be secured to the chuck 3* by bolts, the heads of which engage undercut curved slots 21, Fig. 14, in the block. Fig. 15 shows a modification in which the blocks 17 are formed with curved faces and are secured to a curved holder. Wedges or washers may be used to tilt the lensholders when desired. In solid bi-focal lenses with a ridge between the two surfaces, the ridge is obscured or left unpolished to prevent reflection, and its sharp edge is chamfered to prevent injury when coming in contact with a hard surface. The polishing of the ridge may be prevented by a strip of copper or the like.