GB988309A - Draughting instruments - Google Patents

Abstract

988, 309. Drawing instruments. F. C. MERRIFIELD. Feb. 10, 1964 [Feb. 12, 1963], No. 5498/64. Heading G1X. A portable drawing instrument comprises a base member 12 having a straight edge 24 to contact a T-square or the like, and an undersurface to ride on the drawing work, an arm 22 extending perpendicularly from the straight edge and spaced above the drawing work, a triangular member 14 pivotally connected to and underlying the arm 22 with its undersurface co-planar with that of the member 12, a protector member 16 pivotally connected to and overlying the member 12 and having graduated indicia lines 40 for determining the position of the triangular member 14, and a coupling unit 18 pivotally connecting the members 14, 16 to the arm 22. The member 12 is formed with a step 26, and the arm 22 is held on the step by an adhesive or a fusion joint. The triangle member may have angles of 45 degrees or 30 degrees and 60 degrees, and may be perforated with circular or elliptical holes as tracing guides. The hypotenuse side of the member 14 may be eliminated reducing the member to a pair of right angularly disposed arms. Indicator lines 44, 46, 48 at known angles are marked on the member 14 and co-operate with the indicia marks 40. The member 16 comprises two joined plates 36, 38, this arrangement enabling a reduction in parallax between the marks 40 and 44, 46, 48 to be attained. The coupling unit 18 Fig. 3 is provided with a sleeve 52 forming the pivot for the members 14,16, the member 14 being held in place by a screw 54. The members 14, 16 are held in frictional engagement with the arm 22 by an annular cup member 58 urged downwardly in Fig. 3 by a spring 64. When it is desired to move the members 14, 16 downward force on a plunger 68 pivots accurately spaced fingers 66 about fulcrums formed by slots in the sleeve 52 to raise the member 58 against the spring 64 and so release the members 14, 16 for pivotal movement about the sleeve.