GB563318A - Improvements in drawing instruments - Google Patents

Abstract

563,318. Mathematical drawing- appliances. SIMPSON, J. P., STEWART, J., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. March 25, 1943, No. 4871. [Class 97 (iii)] An appliance for use in the drawing of trimetric projections comprises a flat member provided with at least one edge at right angles to a reference edge, the edges being sets of scale graduations of unit length, at least two other edges inclined at different acute angles in opposite directions and marked with scale graduations which differ from one another and are fractional parts of the said unit length and two further straight edges preferably formed as slots oppositely inclined at acute angles to the reference edge and marked with scale graduations which differ from one another and from the other inclined edges and are fractional parts of the unit length. Fig. 1 shows an appliance having a reference edge 10 and edges 11, 12 at right angles thereto, all of which edges are marked with scales of unit length, e.g. inches, two edges 13, 14 inclined oppositely at different acute angles and marked with scale graduations of different fractional parts of the unit length and four further edges 15 ... 18 formed as two slots and marked with scale graduations which differ from one another and from those of edges 13, 14 and are fractional parts of the unit length. In use, the horizontal and vertical lines of the drawing are drawn along the edges 10, 11 or 10, 12 and to unit scale, the other lines being drawn along pairs of edges 17, 15 or 18, 13 or 16, 14 according to the point from which the object is supposed to be viewed. To obtain other projections the appliance may be used with edge 11 as the horizontal reference edge and also with the appliance reversed, that is, with the normal upper face used against the paper. The Specification also mentions formulµ whereby the scales other than unit ones may be determined.