Geometrical instruments – Straightedge type – Plural straightedges nonadjustably fixed at right angles
Patent
1997-08-09
1999-02-02
Bennett, G. Bradley
Geometrical instruments
Straightedge type
Plural straightedges nonadjustably fixed at right angles
33 1N, 33562, B43L 1300, B43L 1320
Patent
active
058649590
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a drawing triangle or a protractor, in particular for blackboard use.
Known accessories of this type for blackboards 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 damage, in form of breaks between the plane member and the handle, or local damage to edges and points caused by pressure.
U.S. Pat. No. 1,225,464 discloses a spatial, closed pyramid-shaped drawing implement, which has four flat side surfaces having their central parts recessed in such a manner that drawing straight edges are formed along the outer side edges of all four flat sides. In other words this known drawing implement has up to four usable sides and is not suitable for use on blackboards.
SUMMARY OF THE INVENTION
The present invention has for its purpose to provide an improved drawing triangle or protractor for use particularly on a blackboard, which may have extraordinary strength, and which has considerable advantages during use in relation to known accessories for blackboards.
The drawing triangle or the protractor according to the invention is distinctive in that outer side edges of said drawing instruments preferably are provided with scales which define a common ground plane and are adapted to rest against a drawing plane, preferably a generally vertical blackboard, such that the spatial body has a form of a pyramid, of which the triangle side surfaces are provided with preferably triangular openings having the same triangular shape as that of said side surfaces. The drawing instrument further is distinctive in that the handle is provided with material between said openings. In a simple manner there is obtained a drawing triangle or a protractor, which may have extra-ordinarily high ultimate strength, and which during use may have considerable advantages. By way of example, the drawing triangle or the protractor may be made with a reduced consumption of material, resulting in a corresponding low net weight. Furthermore, the drawing triangle or the protractor according to the invention, has among other things, because of its spatial construction an improved balance, which makes it easier to handle the drawing implement. Additionally the hollow, spatial configuration of the drawing triangle and the protractor is formed without projecting parts, which is advantageous because the drawing triangle and the protractor thereby are stackable.
The drawing triangle according to the invention may be so configured that the outer side edges form a right angled triangle with acute angles of 30.degree. and 60.degree.. Alternatively the outer side edges may form a right angled triangle with acute angles of 45.degree.. As another alternative, the outer side edges may form an equilateral triangle with angles of 60.degree..
Appropriately, the protractor according to the invention is so configured that the spatial body has the form of a cone or a spherical segment, in which openings are provided, and that the handle is constituted by material between said openings.
Advantageously the protractor according to the invention may be so configured that it includes an arched ruler stretching about 180.degree. or 360.degree. , and that it is provided with an upright, approximately diametrical transverse rib, which has an under side edge touching the ground plane.
Preferably the handle is constituted by an upright rib stretching from the middle of the transverse rib to the outer side edge.
BRIEF DESCRIPTION OF THE DRAWINGS
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 of a drawing triangle according to the invention, while
FIG. 2 shows a perspective view of an embodiment of a protractor according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The drawing triangle 2 shown in FIG. 1 has an right angle 4, an angle 6 of 30.degree. and
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patent: 4337577 (1982-07-01), Hotchkiss
patent: 4926564 (1990-05-01), Loggins
patent: 4945642 (1990-08-01), Saulietis
Johansen Joern B.
Oellgaard Nis
Bennett G. Bradley
Johansen Joern
Oellgaard Nis
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