GB676890A - Improvements in and relating to drawing or inscribing instruments - Google Patents

Abstract

676,890. Drawing-instruments. ASTON, A. C., and CATENBY, D. C. B. Oct. 5, 1950 [Oct. 13, 1949], No. 26338/49. Class 97 (iii). [Also in Group XV] An instrument for drawing parallel lines comprises a series of scribers 7, Fig. 1, arranged in a carrier 3 which is rotatably mounted in a tablet 1 having a datum edge 1a for guiding the instrument along a given path so that a series of parallel lines are drawn whose spacing depends on the angular disposition of the carrier to the tablet. The cylindrical carrier 3 is screwed to a disc 3b, Fig. 2, which rotates in a rebate 2a in the under-face of the tablet. The scribers 7 are mounted in spring-jawed chucks 5 housed in bores 4 in the 'carrier and passing through apertures 2, 3c in the tablet 1 and disc 3b respectively. Springs 6 act between shoulders 4b of counterbores 4a and the upper surfaces of enlargements 5b on the chucks. A scriber may be rendered inoperative by withdrawing the chuck to a canted position in which the lower end edge 6a thereof rests on the rim of the hole 3c. A linear scale is provided on the bevelled edge 1b and an angular one 1d on the tablet co-operates with index marks 3d on the carrier. A lead sharpener (see Group XV) may be provided and housed in a recess and bore 9 in the carrier or tablet, the rod of the sharpener frictionally engaging the bore or being secured by screw-threaded means. The carrier or tablet may also be provided with a pocket for spare leads covered by a pivoted or sliding shutter. In a modification, the scriber carrier is releasably secured to the disc by a spring catch or by replacing the screws with spring expanding dowel pins, thus enabling alternative carriers to be substituted. In a further modification, to facilitate the use of the instrument with curved guides, the edge la is provided with spaced bearing projections such as small rollers mounted on vertical axes or a pair of freely running balls. In modifications described in the Provisional Specification, the upper surface of the carrier has a diametrical slot, the vertical bores being made from the base thereof, and each chuck is limited in its downward movement by a nut screwed to its upper end, the nut being prevented from rotating by lying in the slot. The scriber carrier may be seated into the central aperture of the tablet or may have a circular rebate for entering the same and a sliding index may be provided at the bevelled edge of the tablet for convenience in setting the instrument. The series of scribers may be mounted in a radial arm pivoted centrally or at one end for varying the angle of the series. One end of the arm may have a locking device co-operating with an arcuate slot in the tablet and a slidable index may be provided for setting the instrument.