Patent GB-593759-A (GB)
Title: Improvements relating to the formation of curved surfaces of prescribed figure by grinding and/or polishing
IPC: B24B17/00
Filed: 1945-03-19
Abstract: 593,759. Grinding and polishing lenses. BURCH, C. R., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. March 19, 1945, No. 6866. [Class 60] Apparatus for grinding and/or polishing an object or specimen to form thereon a curved surface of prescribed figure of revolution symmetry comprises means for mounting the specimen for rotation about a fixed axis, a grinding and/or polishing surface arranged for yieldingly bearing against the surface of the specimen over an effective area of contact which is of small dimensions and a mere fractional part, namely of the order of 5 per cent or less, of the prescribed surface, means for reciprocating said grinding or polishing surface in a general plane through said axis, and means for causing said grinding or polishing surface to tend to assume substantially such orientation about an axis at right angles to the plane of reciprocation at any location in its traverse as it would have for the same location in its traverse in contact with the actual surface of prescribed figure. The work 1, such as a lens or mirror of glass or other suitable matter, which is to be made aspherical, is seated in a cell 2 mounted on a hollow spindle 3 rotatable in a bearing 4 which may be adjustable. The work is operated upon by a pad 6 which for grinding may be of glass or any of the usual metals, with carborundum or other abrasive in water, glycerine or other liquid vehicle ; for polishing, the pad may be of cork (hard rather than soft) or wood (soft rather than hard) with rouge and water, or pitch and beeswax on wood or in cork with rouge and water. The pad 6 is fastened to a bar 5 pivoted about a horizontal axis, the centre of the pad lying substantially in alignment with the pivotal axis of the bar. The pivots for the bar 5 are carried by a pair of links 8 pivoted at 9 to a carriage 10 movable in slides 11 on table 12. Reciprocation of the carriage 10 is effected by link 15 pivoted at 16 to the carriage, its other end being connected to a pivoted arm 18 which is oscillated by connecting rod 19 and crank 20. The end of the link 15 is adjustably secured in a curved slot 18a in the arm 18, whereby the amplitude of reciprocation can be varied ; the pivot 18b of the oscillating arm is moved by a motor 26 and lead screw 25 to give continuous creep of the mean position of the reciprocation. The pad may be pressed on the work by gravity alone, or a spring 28 may be provided carried by the carriage 10 and bearing on a lug 5a projecting from the pad-bar 5. To the latter is rigidly connected a rod 29 which is nominally perpendicular to the tangent plane at the centre of that surface of the pad 6 which is adapted to contact with the work 1. The rod 29 engages a cam 30 having a shaped surface 30a whose profile is the evolute of the prescribed surface to be formed on the lens 1 ; the cam is universally mounted at 31 to enable horizontal and vertical adjustment. The rod 29 is urged into engagement with the cam surface 30a by means of spring 29a. To enable optical tests e.g. the Foucault knife-edge test, to be applied at frequent intervals to determine the necessary adjustments to the pad traverse stroke and creeping limits without removing the work, the work holder 2 carries a screen 32 formed with a pin-hole 32a and a lens 33 mounted coaxially with the work 1 by means of tube 34 secured to the screen, a light beam being projected through the hollow spindle 3 on to the lens 33.