GB652927A - Improvements in or relating to dividing tables - Google Patents

Abstract

652,927. Dividing-engines; scale-reading apparatus. OPTICAL MEASURING TOOLS, Ltd. Jan. 14, 1948, No. 1159. [Classes 97 (i) and 97 (iii)] [Also in Group XXII] In a rotatable dividing table 10 having a graduated circular scale 19 located in a supporting base, and an optical system for projecting a magnified image of an illuminated portion of the scale on to a screen 71, means for determining the angular setting of the table are provided comprising a normally-fixed graticule 67 provided with an index 74 and with a single degree reference scale 68, and a movable subdivided scale in the form of a graticule 66 engraved on the outer face of the outer prism 64 of a laterally movable prism system 44, 64. The prism system and projection lens system 45 are mounted on a main cradle 46 which is laterally adjustable relatively to the objective lens system 39 so as to allow the image of the graticule 67 to be moved relatively to the scale image thereby facilitating reading of the table setting on the screen, and the prism system is mounted on a sub-cradle 43 which is carried by the main cradle and is laterally adjustable thereon so as to allow the image of the graticule 66 to be moved relatively to the image of the graticule 67. The table 10 is rotatable by a worm and worm-wheel drive 80, 81 the worm-shaft 82 being rotatable by a hand wheel 95 either directly or indirectly with speed reduction through an epicyclic gear. The worm may be disengaged from the worm wheel so as to allow the table to be freely rotated for rough adjustment to the angular setting. To set the table initially at a zero reading on the screen, the main cradle 46 is moved laterally until an image of the scale 68 appears centrally on the screen when the cradle is located in position. The sub-cradle 43 is then moved laterally until the image of the zero line of the graticule 66 coincides with the image of the index 74 when the sub-cradle is locked in position. The table is then rotated freely until the image of the zero degree line of the scale 19 is at least in the vicinity of the screen, then rotated by the hand wheel 95 and direct drive until the zero degree line sets conveniently near the zero pair of lines of the image of the scale 68, and finally by the hand wheel 95 and indirect drive until the zero degree line image sets exactly midway between the zero pair of lines of the image of the scale 68. To rotate the table through an angle of, say, 15 degrees 471 3611 from the zero reading, the table is rotated freely to move the image of the 15 degrees line of the scale 19 to approximately the desired position, then by the hand wheel and direct drive to move the 15 degree line midway between the pair of lines of the reference scale image indicating the 40<SP>1</SP> mark. The sub-cradle 43 is then unlocked and moved until the 71 36<SP>11</SP> mark of the graticule 66 coincides with the index 74 when the subcradle is again locked. The 15 degree line image has moved slightly away from its position between the 40<SP>1</SP> pair of lines during the movement of the graticule 66, and upon moving it back again between the 40<SP>1</SP> pair of lines by using the hand wheel 95 and indirect drive, the table will have been rotated through exactly 15 degrees 47<SP>1</SP> 36<SP>11</SP>. The table is locked in its set position by means of knobs 109, 110.