[0001] The present invention relates to a set square.
[0002] Set squares in general are well known. The usual form is that of a right angled triangle
whose other angles are both 45° or are 60° and 30°. The square is commonly made of
a plastics material or metal.
[0003] Numerous proposals have been made to render set squares more versatile. However none
of these seems to have had any success. This is probably because they either add little
to the potential utility of the square, or because they are so complicated as to frighten
off potential users and/or to increase manufacturing costs substantially.
[0004] For example, U.S. Patent 2,043,729 (Bilder) discloses a 90/45/45° set square having
three cut-outs which provide various straight edges at predetermined angles to external
edges. There are also numerous apertures for use in drawing circles, and a protractor
scale. The whole is of dauntingly complicated appearance, and would apparently require
much practice to master. U.S. 1,598,690 (Petronio) discloses a 90/60/30° set square
with three apertures (a slot and two triangles) for providing further angles. The
triangles are right-angled, with the perpendicular sides parallel to those of the
set-square. Thus only the hypotenuses provide additional angles. Generally, a given
angle is obtainable only relative to one particular external side. Thus the user must
locate the square the correct way up, and select the correct aperture. There is also
a protractor scale, symmetrical about the 90° angle of the square, its origin indicated
by an aperture.
[0005] Further examples of patent specifications disclosing modified set-squares are:
French 908163 (Vardanian)
French 934943 (Le Material Automatique Electrique)
French 957869 (Lewin)
French 981857 (Cordani)
French 1124247 (Balloche)
French 1208614 (Hoellinger)
French 2351801 (Bord)
U.S. 1845449 (Smith)
U.S. 3375589 (Dolgorukov)
Swiss 276736 (Clerc)
G.B. 794192 (Midulla)
[0006] According to the present invention there is provided a substantially triangular set
square having three external straight edge portions with angles of 30°, 60° and 90
^{0} defined by respective pairs thereof, and an internal substantially triangular aperture
having respective straight edge portions which define angles of 15° and 45° with each
of the external straight edge portions.
[0007] By means of such a set square, a draughtsman using a T-square can set the four usual
angles (30,45,60,90°), and also obtain angles of 15° and 75
^{0}.
[0008] Preferably the straight edge portions of the aperture define a 30°, 30°, 120° triangle.
Then a user, even without a T-square, can set angles precisely. Angles can be drawn
easily and accurately, particularly interior angles of the aperture, but also angles
formed by one side of the cut-out and one external edge portion. Use of the interior
angles to draw vertices is of course not affected by the degradation of the external
corner portions of the square, which commonly happens in use.
[0009] Preferably there are means indicating a straight line at right-angles to one of the
external straight edge portions other than that defining the hypotenuse, said line
traversing the aperture. This line can be used to set 45, 60, 75 and 90° angles precisely,
without the need for a T-square. The line is then used as a reference instead of an
external edge/portion.
[0010] Preferably there are means defining a protractor scale arranged so that the origin
of the protractor is at the intersection of said line and the straight edge portion
at right angles thereto, said line indicating the 90° line of the protractor. Having
the origin of the protractor at the edge makes the protractor particularly simple
to use, e.g. for setting the square at any desired angle to a given line.
[0011] The versatility of the implement can be increased by providing one or more of the
edge portions with measuring scales and/or by providing a plurality of holes at predetermined
spacings for receiving pencil points for drawing arcs of predetermined radii.
[0012] There may be indicia indicating the angular relationships of at least some of the
straight edge portions.
[0013] Some preferred embodiments of the invention will now be described by way of example
with reference to the accompanying drawings, in which:
Fig.1 is a plan view of a preferred embodiment of a set square according to the invention;
Fig. 2 is a section along XY in Fig.1; and
Fig. 3 is a schematic view of a second embodiment.
[0014] The set square 1 shown in Figs. 1 and 2 has the general form of a 30/60/90° triangle
ABC, having sides a and c at right angles, and side b as hypotenuse. Angles A and
C are 30° and 60° respectively. An aperture 2 has the form of a 30/30/120° triangle
PQR, the sides p and r and the angles P and R being equal. It is oriented so that
its longest side q is adjacent the hypotenuse b, and makes an angle of 150 therewith,
approaching nearer it towards the vertex C.
[0015] Thus, the single cut-out 2 provides angles of 15
^{0} and 45° to each external side a,b,c as follows:
[0016] Angles of 75
^{0} to sides a and c are also provided, by sides r and p respectively.
[0017] As indicated at 6, the square 1 may bear indicia for showing the user where to obtain
various angles.
[0018] A line 3 is indicated (suitably by an inked indentation), extending at right angles
to edge c from a point 0 thereon. The line 3 is interrupted by the aperture 2, and
continues on the other side thereof until it reaches an arcuate slot 4 furnished with
protractor scales 5. The slot and scales have their centre of origin at 0. The edge
c and the line 3 are respectively the 0/180° and 90° lines of the protractor. Thus
the square 1 can easily be positioned at any desired angle to a given line. Although
the slot 4 extends only over about 95° , angles up to 180° can be measured or set
by using either the edge c or the line 3 as the reference line. Having the line 3
traverse the aperture 2 makes it easy to align with a line on a drawing even if the
square 1 is opaque.
[0019] The longer external sides b,c are provided with scales 7 graduated in inches and
centimetres respectively. Adjacent side c is a line of small apertures 8: five with
2mm spacings, seven more at 1cm spacings, and another 7cm from the last of these.
The apertures 8 are dimensioned to receive pencil points with minimal play, so that
arcs of known radii can be drawn using two pencils.
[0020] This instrument design does not necessitate transparency, and it may be manufactured
in any suitable material such as metal or plastics by any conventional means. If sheet
metal or plastics is to be used, section X-Y in Fig.2 shows typically how its structure
can be stiffened to minimise the material thickness and weight, and also provide additional
benefits. A fold 9 can be pressed or moulded all round the periphery of the instrument,
resulting in bevelled edges 10 for the scales 7. This not only provides stiffening,
but improves the appearance, and also enables the instrument to be used face down
with advantage when using pen and ink, to discourage running of the ink as may occur
with a flat surface against the paper.
[0021] Although the arrangement shown in Fig.1 is felt to be particularly useful, others
are possible and may oe favoured in some circumstances. Other shapes and orientations
of the aperture 2 are possible, while still giving the desired angles with the external
sides. Thus Fig.3 shows an alternative arrangement with an aperture 2' formed as a
30/60/90° triangle XYZ with sides x,y,z. The hypotenuse y is at 15° to side b, and
45° to side a. The shortest side z is at 15° to side c, and 45° to side a. The other
side x is at 15
^{0} to side a and 45° to side b.
[0022] While the invention has been illustrated above with reference to preferred embodiments,
those skilled in the art will understand that various changes may be made without
departing from the spirit and scope of the invention, and it is intended to cover
all such changes and modifications by the appended claims.
1. A substantially triangular set square (1) having three external straight edge portions
(a, b, c) with angles of 30°, 60° and 90° defined by respective pairs thereof, and
an internal substantially triangular aperture (2), characterised in that the internal
aperture (2) has respective straight edge portions (_{E}, g, r) which define angles of 15° and 45° with each of the external straight edge
portions.
2. A set square according to claim 1 wherein the straight edge portions (p, q, r)
of the aperture (2) define a 30°, 30°, 120° triangle (PQR).
3. A set square according to claim 2 wherein the edge portion (g) of the aperture
(2) which is opposite the 120° angle (Q) is at 15' to that external edge portion (b)
which defines the hypotenuse.
4. A set square according to any one of the preceding claims having means (3) indicating
a straight line at right-angles to one of the external straight edge portions (c)
other than that defining the hypotenuse (b), said line traversing the aperture (2).
5. A set square according to claim 4 further including means defining a protractor
scale (5) arranged so that the origin of the protractor is at the intersection of
said line (3) and the straight edge portion (c) at right angles thereto, said line
(3) indicating the 90° line of the protractor (5).
6. A set square according to any one of the preceding claims wherein at least one
of the straight edge portions (b, c) is provided with a measuring scale (7).
7. A set square according to any one of the preceding claims wherein the set square
is provided with a multiplicity of apertures (8) at predetermined spacings for receiving
pencil points for use in drawing arcs.
8. A set square according to any one of the preceding claims having a peripheral channel-section
portion (9) whose outer margin (10) is arranged to form a bevelled edge of the square
(1).
9. A set square according to any one of the preceding claims bearing indicia (6) indicating
the angular relationships between at least some of the straight edge portions (e.g.
p/a; g/a; r/a).