GB351728A - Improvements in mathematical instruments - Google Patents

Abstract

351,728. Protractors. BUCHANAN, A., 19, Routh Road, Wandsworth, London. June 16, 1930, No. 18429. [Classes 97 (ii) and 97 (iii).] A mathematical instrument comprises a protractor and a set-square capable of relative turning movement, wherein the protractor is in the form of a semi-annulus provided with a straight edge on its base, and is slidably mounted in a slot in the set-square, so that the set-square bears on the two arcuate edges of the protractor. As shown in Fig. 1, a set-square 1 pivots about the centre 3 of a semi-annular protractor 2, graduated round its outer semicircular edge in the usual manner, and also having graduations indicating the slopes of parts of capital letters and roof pitches respectively. The graduated ruler 4 is preferably reinforced with metal. The set-square 1 is composed of two frames 9, 10, Fig. 2, one on either side of the protractor 2, and two intermediate pieces 11, 12 of substantially triangular form having arcuate edges conforming to the corresponding edges of the protractor 2. A clamping device comprises a shoe 14 pressed against the edge of the protractor by means of a screw 15 passing through a nut 16 mounted on the set-square 1. A spring may be used instead of or in addition to the screw and nut. A small hole may be provided at the centre 3 in which a thread provided with a weight may be inserted to form a clinometer. The piece 11 may have a hair line 20, or may have its arcuate edge graduated to form a vernier scale, or may be graduated to co-operate with a hair line on the semi-annulus 2. The midway graduation on the protractor 2 may indicate 45 instead of 90‹. The edges 7, 8 and those of the straight edge 4 may be tongued to facilitate use with an ink-ruling pen. A set-square of any shape may be used.