Patent GB-654709-A (GB)
Title: Improvements in and relating to devices for measuring distances on charts and the like
IPC: G01B3/12
Filed: 1948-07-13
Abstract: 654,709. Measuring-wheels for charts &c. OWEN, H. E. L., and GURTON, H. T. July 13, 1948, Nos. 18797/48 and 16199/49. [Class 106 (ii)] A device for measuring distances on charts comprises a tubular holder with a longitudinal slot and a chart wheel rotatably mounted in the holder so as to engage threaded means held against axial movement, which co-operates with threaded means held against rotation and carrying a pointer extending into the slot to indicate distance against a scale registering with the slot and carried with other alternative scales by a sleeve adjustably mounted on the holder. The toothed chartwheel 14 is rotatably mounted on a pintle 16 in an extension 12 of a tubular casing 10 in which is journalled a screw-threaded rod 18 having fixed thereto a gear-wheel 22 engaging the wheel 14 so that traversing the latter over a chart causes rotation of the rod 18 which, being prevented from axial movement by collars 34, causes a nut 24 carrying a pointer 30, constrained in a longitudinal slot in the casing, to move axially and indicate the distance represented on the chart against scales adjacent to the slot. A scale sleeve, which may be located by spring rings 38 clipped in grooves 40 in the holder, has a slot to register with the slot 26 which is marked with a different scale along each edge and may have two scales on each side of the mid-point of the slot being interchangeable by reversing the sleeve and the sleeve may have other slots provided with scales. The sleeve may be of plastic, celluloid or metal and if transparent may be spaced from the holder clear of the pointer. To facilitate re-setting, the nut 24 has a sector 48 removed and the rod 18 is sufficiently flexible to be pressed down free from the thread of the nut against a spring 58 which normally holds the rod in axial alignment in a cap 50, having a central bore and a radial slot 56. Alternatively the cap 50 may be retained on the holder 10 by a grub-screw 74 working in a slot 76 in the holder 10 so that the cap 50 may be turned to bring the slots 56, 48 into or out of alignment. A cover 63 protects the wheel 14 when not in use and a cover 64 may hold the scale sleeve in position. In a modification, the chart wheel has a conical circumference which may be milled and is integral with a gear-wheel meshing with an idler which engages the gear 22. The chart wheel 14 may be removably journalled by means of a lock-nut in the extension 12 of the holder 10 which may have several bores for the pintles of different sized chart wheels 14 or which may be adjustable on the holder 10. The spare wheels are preferably complete with pintles which may have brackets holding them and the cover 63 may be provided with a removable container for housing the spare parts. In another embodiment the rod may be movable axially and held against rotation, while the nut is held against axial movement but is free to rotate and is connected to the gear-wheel 22, the pointer being carried by the rod. The scale along one side of the slot may be extended in the opposite direction along the opposite side, the wheel 14 being run in the opposite direction in conjunction therewith. The chart wheel may be mounted on a pivoted bracket and act like a castor. The scales may be graduated in units other than distance.