Patent GB-584737-A (GB)
Title: Improvements in or relating to gauging or measuring instruments
IPC: G01B5/20
Filed: 1944-03-07
Abstract: 584,737. Gauges. SEARS, J. E. March 7, 1944, No. 4212. [Class 106 (ii)] In a comparator for three-dimensional objects, a master object and an object to be tested can be simultaneously and similarly moved through a range of positions, and supports of two styluses can be simultaneously and similarly moved in relation to the objects to bring the styluses into contact with corresponding points on the surfaces'of the objects. The stylus contacting the master object is maintained in a determined position in relation to its support, which is arranged to urge the stylus against the object with a light pressure. The other stylus has freedom to adapt itself under light pressure to contact the other object and in so doing to operate means to indicate or record any variation from the master. The instrument is adapted for measuring as distinct from comparing. The objects are mounted on mandrels 58 arranged-between centres carried in tailstocks 2t, 3t and headstocks 2h, 3h mounted on the base 1. An intermediate carriage 8 is slidably mounted on the base for movement by a lead screw 11, the mounting including a V guide 9 and a flat guide 10. The headstock spindles carry gear-wheels 12, 13 meshing with an intermediate loose wheel 14. By means of clutches 53, 54, either or both the wheel 14 and the lead screw 11 may be rotated by a hand wheel 48. An upper carriage 15 is mounted for transverse movement on the carriage 8. The mounting comprises two parallel V grooves in the carriage 8 containing balls, and corresponding bearing surfaces, one of V-form and the other flat, in the carriage 15. Styluses 23, 22 for contacting the objects are carried by holders 33, 24 mounted on the carriage 15 by means of pairs of vertical thin steel strips reinforced, except near their ends, by thicker strips. The base 1 is supported by screwed feet 20 which are adjusted to tilt the instrument so that the styluses bear on the objects with a light pressure. The holder 24 carries an adjustable screw contacting one arm of a bell-crank lever 28 pivoted on crossed springs. Movement of the holder is transmitted through the lever to a dial indicator 32. If no provision were made for correction of errors in the master object and the instrument the stylus 23 would be rigidly mounted in its holder. To correct errors, the holder 33 is provided with an adjustable stop 38 abutting an arm 36 of a bell-crank lever pivoted on crossed springs 37. The other arm of the lever carries a roller 39 supported on a plate 40 pivoted at one side of its top surface by crossed springs to the carriage 15. The. underside of the plate is engaged by a rod 42 carried by a lever 43 pivoted at one end by crossed springs to the carriage 8 so that it can move in a vertical plane. The other end of the lever carries an adjustable follower 45 resting on a cam 46 carried between a headstock 46h and a tailstock 46t and adapted to be driven by a gear-wheel 47 meshing with the gear 13. The cam is designed to compensate for ascertained errors in the master object and the instrument itself. Setting of the stylus gear is achieved by aligning the holders and the plane through the centres 4-7 by means of a fitting bar adapted for mounting in the stylus holders and engaging transverse holes provided in the mandrels. To enable the instrument to be used for measuring as distinct from comparing a graduated hand wheel 66 is provided on the lead screw, so that in conjunction with a scale 67 on the base and a co-operating index 68 on the carriage 8 it serves as a micrometer, the headstock 70 and the carriage 15 may be operated by means of a graduated hand wheel 76 which in conjunction with a scale 78 .on the carriage 8 also serves as a micrometer. The hand wheel 76 actuates a sleeve 71 abutting a stop on the carriage and is prevented from rotating by a projecting arm 73 carrying a roller engaging guide plates 75 profiled or inclined if necessary to compensate for errors in the micrometer screw. To ensure correct relative positions, the mandrels and the cam are provided with setting marks and microscopes for viewing these are provided.