Patent GB-585806-A (GB)
Title: Improvements in and relating to optical dividing heads
IPC: B23Q17/24
Filed: 1943-11-08
Abstract: 585,806. Dividing-engines. HILGER, Ltd., A., DOWELL, J. H., STERNBERG, R. S., HERBERT, Ltd., A., and CURSON, T. Nov. 8, 1943, No. 18525. [Class 97 (iii)] [Also in Group XXII] A dividing head For use in cutting gears, grinding splined shafts, or other machining operations or for testing angular settings, has a polygonal arrangement of reflecting surfaces in relative rotational relationship with a collimating device which gauges the normality or approximation to normality of any of the reflecting surfaces and also has a second polygonal arrangement of reflecting surfaces arranged at slightly different angles to the first set so as to provide a vernier in conjunction therewith. The head comprises a base A in which is rotatably mounted a spindle 1, actuated by a hand-operated worm 39 and worm-wheel 40, carrying an angularly graduated plate 37, and a polygon 2 having reflecting surfaces 3 arranged at angles of 18 degrees to each other. A semi-polygon 4 having reflecting surfaces 4a at 20 degrees to each other is supported approximately coaxial with the spindle on balls' 9, Fig. 3, and is pressed by springs 7, 10 against fixed pins 8 and a movable pin 5 adjusted by a micrometer head 6 to vary the angular position of the reflecting surfaces 4a relatively to the surfaces 3. The distance of the pin 5 from the pins 8 is adjusted by screws 12. The reflecting surfaces 3, 4a are observed by the collimating device comprising a source of light 16 from which light is projected by a condenser 17, prism 18, mirrors 14, 15 and an object glass 13. A plate 19 engraved with a scale 20 having sub-divisions of 1 degree marked in minutes, as shown in Fig. 5, and with indicators 21, 22 spaced at a 1-degree interval on the other side of the zero, is mounted on the prism 18 so that an image of the scale and indicators will be reflected from the surfaces 3, 4a respectively, passed through a collecting lens 28 and transmitted by mirrors 29, '30 to a diffusing screen 32 which may beobserved through a magnifying lens 33. The mirrors 14, 15 are arranged so that the indicator 21 is imaged opposite the zero of the scale 20, as.shown in Fig. 5, when the two surfaces 3, 4a being viewed are exactly parallel in the zero position. The collimator and light-projecting system is rotatable with a base 34 about an axis approximately coincident with that of the polygons and spindle 1 and the angular settings are indicated by an arcuate scale 35 and an index on the base 34. In making an angular setting of the spindle 1, the spindle and polygon 2 are first rotated by the worm 39 until the required angle is registered on the scale 37 to the nearest two degrees. The collimator is then rotated to bring its light beam opposite the appropriate mirrors on the polygons 2, 4 which are parallel, this setting being indicated by the scale 35, and the worm 39 is then actuated to rotate the polygon 2 until one of the indicators 21, 22 (depending on whether an even or odd number of degrees is being measured), comes exactly in line with the zero of scale 20, thus indicating that the appropriate mirrors on the two polygons are exactly parallel and that the spindle 1 and the work mounted thereon have been turned through the exact number of degrees. To set the spindle 1 to a further sub-division of one degree, the polygon 2 is rotated to bring the indicator 21 or 22 opposite the required number of minutes on the scale 20, and for setting to seconds of angle, the polygon 4 is adjusted by the micrometer head 6 graduated in seconds. In a modification, a metal disc 41, Figs. 7 and 8, replaces the polygon 2 and has double-sided mirrors 42 attached thereto so as to project to one side of the disc, the mirrors being held by springs 45 and a clamping ring 44 against supporting surfaces, each consisting of three small projections 43 on the disc. Each mirror is arranged at 40 degrees to the adjacent one and may be of metal such as stainless steel or of glass, quartz or fused silica coated with highly reflecting medium such as rhodium, chromium or aluminium. Since the number of mirrors is odd, the 20-degree spacing of Fig. 1 may be obtained by directing the collimator against the inner surfaces of the mirrors on one side of the'disc and the outer surfaces on the other side. An arrangement such as that shown in Fig. 7 may be used with double the number of mirrors spaced at 20-degree angles, the inner reflecting surfaces only being used, as shown in Fig. 10, and the collimator objective 52 being coaxial with a conical polygon 51 having reflecting surfaces arranged at 45 degrees to the collimator axis and at 36 degrees to each other. Light from the collimator is reflected by the polygon 51 on to one of the mirrors 48 and back to the polygon and then to the collecting lens and screen. In this case, the scale 20 of Fig. 5 is replaced by a stationary scale consisting of radial lines and concentric circles, Fig. 12, reflected by an end surface 61 of the vernier polygon and the indicators 21, 22 are replaced by a spot 63 and an arcuate line 64 which are caused to move across the stationary scale as the polygon mirrors 48 are rotated together with the dividing head spindle 47. The indicators 63, 64 are reflected by the inclined surfaces of the vernier polygon 51. The vernier polygon 51 may be attached to the spindle 47 and the polygon 46 carrying the mirrors 48 may be fixed, the end reflecting surface 61 then being separate and non- rotatable. The dividing head spindle may be locked after adjustment by a screw 70, Fig. 1, and the images of the scale and indicators reflected by the mirrors 14, 15 may be brought into proximity with each other, as shown in Fig. 5, by known optical devices such as two thick glass plates inclined to each other, one having a highly polished edge slightly behind the other. Specification 560,325 is referred to.