Patent GB-601961-A (GB)
Title: Improvements in or relating to the production of engine-divided scales
IPC: G03F7/20
Filed: 1944-06-16
Abstract: 601,961. Dividing-engines for marking graduations. MEECH, F. B., and OPTICAL MEASURING TOOLS, Ltd. June 16, 1944, No. 11547. [Classes 97 (i), 97 (iii) and 98 (ii)] The individual graduations, or small groups of adjacent graduations, are produced successively on a photo-sensitive surface by projecting an illuminated image of a mark, or group of marks, on to the surface and shifting the image and surface relatively to one another by dividing-engine mechanism between the successive exposures. As shown in Fig. 1, the sensitized glass plate 18 is mounted by clips on a removable table top 17, which may be secured by bolts at 16 to a circular table 14. The latter is mounted by a roller bearing 15 on a cylindrical casing 12 secured to the base 10 and may be rotated about its axis X-X by a worm-wheel 19 and fine adjustment worm operated by the knob 20. A graduated annular glass ring 21 is secured to the bottom of the worm-wheel 19. Part of the silvered scale on the ring 21 is illuminated by a source 50, Fig. 2, prism 22, and objective 23, and an image thereof is formed by the objective 23, prism 24, and prism 25 in the plane of a graticule 26, having two hair lines extending parallel to the projected image of the graduation or the scale 21. The graticule 26 may be moved in a direction at right angles to the hair lines by a micrometer screw 27, Fig. 1, in order to introduce corrections for the known inaccuracies of the scale on the ring 21. The graticule and image of the graduation on ring 21 are projected together by eye-piece 28, prism 29, and' mirror 30 on to a ground glass screen 30a. In use the table 14 is rotated by the knob 20 until the screen 30a shows the desired graduation on ring 21 to be mid-way between the two hair lines. The projector 37, 38 for projecting a reduced image of a slit in the screen 44 on to the plate 18, is carried by a slider 34, which is mounted on a bridge 31 so as to slide along a diameter of the table 14. A knob 35 enables the slider to be adjusted to a desired radial position over the plate 18. The lower tube 38 may be adjusted axially by the knob 39 for focussing, a gauge 45 interposed between the plate 18 and the bottom of the tube 38 to indicate the correct position. A shutter in the lamp housing 37 is opened to effect each exposure. Before the plate 18 is exposed it may be soaked in distilled water for fifteen minutes and then in 90 per cent industrial methylated spirits for fifteen minutes. The plate is exposed after drying, and developed by a reversal process. Contact. prints may then be made on glass plates covered by a bichromated " process " glue containing colloidal silver chloride. After developing in warm water the print is further treated with a photographic developer to blacken the silver and then with an intensifier solution. The print is finally baked at 250‹ C. so that the coating becomes enamelled firmly on to the glass. The figuring of the scales may be effected by replacing the screen 44 by screens bearing the figures required. Alternatively the figures may be on a strip of kinema film fed automatically at the appropriate rate.