The present invention relates to a drawing triangle or a protractor, in particular for blackboard use, and of the type described in the introductory part of claim 1.

Known accessories for blackboards of this type consist normally of several parts, namely plane members with different shape - such as triangular, circular or semi¬ circular plane members provided with handles. Such a construction may cause damages in form of breaks between the plane member and the handle or local damages of edges and points caused by pressure.

The invention has for its purpose to provide an improved drawing triangle or protractor of the type mentioned in the introductory part, which may have extraordinary strenght, and having considerable advantages during use in relation to known accessories for blackboards.

The drawing triangle or the protractor according to the invention is destinctive in that it is provided as a three-dimensional, spatial body, where outer side edges of said rulers preferably provided with scales defines a common ground plan being adapted to rest against a drawing plane, preferably a generally vertical blackboard. In a simple manner it is hereby obtained that a drawing triangle or a protractor, which may have extra- ordinary high ultimate strength, and which during use may have considerable advan¬ tages. By way of example the drawing triangle or the protractor may be made with a reduced consumption of material resulting in a corresponding minor net weight. Furthermore the drawing triangle or the protractor according to the invention has among others because of its spatial construction an improved balance, which makes it easier to handle the drawing implement.

Appropriately the drawing triangle according to the invention is such provided, that the spatial body has form as a pyramid, of which the triangle side surfaces are provided with preferably triangular cuttings having the same triangular shape as that of said side surfaces, and that the handle is constituted by material between said cuttings.

Drawing triangle according to the invention may be such provided that the outer side edges form a right angled triangle with acute angles of 30° and 60°. Or the outer side edges may form an right angled triangle with acute angles of 45°. Alternatively the outer side edges may form an isosceles triangle with angles of 60°.

Appropriately, the protractor according to the invention is such provided that the spatial body has form as a cone or sperical segment, in which cuttings are provided, and that the handle is constituted by material between said cuttings.

Advantageously the protractor according to the invention may be such provided, that the arched ruler is stretching about 180° or 360°, and that it is provided with an upright, approximate diametral transverse rib, of which an under side edge touch said ground plan.

Preferably the handle is constituted by an upright rib stretching from the middle of the transverse rib to the outer side edge.

The invention is explained in more detail in the following with reference to the drawing, in which: -

Fig. 1 shows a perspective view of an embodiment for a drawing triangle according to the invention, while

Fig. 2 shows a perspective view of an embodiment for a protractor according to the invention.

The drawing triangle 2 shown in Fig. 1 has an right angle 4, an angle 6 of 30° and an angle 8 of 60°. The sides 10 and 12 enclosing the right angle of the drawing triangle are provided with scales as rulers constituted by lower outer edges of triangular side surfaces 14, 16, 18. The drawing triangle 2 is provided as a spatial pyramid-shaped body, as the triangular side surfaces 14, 16, 18 are provided with mainly triangular cuttings 20, 22, 24.

At the top of the pyramid-shaped body ribs 26, 28, 30 are formed constituting the handle 32 of the drawing triangle. In some distance from the acute 30° angle a central hole 34 is provided, serving as suspension of the drawing triangle on a wall mounted mounting.

The drawing triangle 2 is preferably manufactured by die casting in a suitable tough, durable plastic material. Or the drawing triangle may be made from a plastic plate by vacuum forming and subsequent copy-milling.

The protractor 36 shown in Fig. 2 is also preferably manufactured by die casting in a suitable tough, durable plastic material. The protractor 36 is provided as an open, spatial body with form as a cone or sperial segment, which along its circumference is provided with a calibrated ruler 38. The cone or sperial segment plane is provided with three cuttings 40, 42, 44, so that a central bend rib 46 is formed, which is suitable as handle 48, and a diametral rib 50, the lower side edge 52 of which is placed in level with the periphery outer edge of the ruler 38, that is that the rib 50 is adapted together with the ruler 38 to rest against a drawing surface, for instance a generally vertical blackboard.

In the middle on level with the handle 48 or the rib 46 the cutting 40 is provided with a semi-circular recess 54 (or a hole) for suspension of the protractor 36 on a projecting part of said wall mounted suspension mounting.

An alternative protractor may be mainly semi-circular, that is that it does not comprise the semi-circle ruler opposite handle 48; and it then might be provided with a central hole in the semi-circle ruler for suspension of the protractor.

It will be within the scope of the invention to provide other shapes of the drawing triangle or the protractor for blackboard use, where there is worked with an open spatial body with a common outer edge-formed resting surface, and where a central handle is provided in distance from the resting surface. It will also be within the scope of the invention to provide corresponding drawing triangles or protactors in minor versions for table use.