The present invention relates to a compass, particularly to a draughtsman
compass of the type usually called bow compass or spring bow compass.
The bow compass is a compass adapted to draw circles or sections
of circles of small radius and it is generally provided in two basic types.
A first type of bow compass has two hinged rods holding a point at
each of their lower ends; one of the points can be substituted by a lead holder
or a drawing pen.
A threaded bar has one end fastened to a median portion of one of
the rods and engages a ring associated to the other rod but adapted to be rotated
to finely adjust the distance between the two rods.
In the other type of how compass, a rod element has a longitudinal
bore in which a point is slidable along its longitudinal axis; a resilient member
is associated to the rod element and its distance from the rod element itself,
i.e. the aperture of the compass, is adjusted by means of a screw. A lead holder
or a drawing pen can he fastened to the resilient member.
British Patent No. 448.202 discloses a drawing compass wherein the
legs are connected together by means of a link having an end engaging a slot in
one of the legs.
The bow compasses of the prior art are susceptible to improvements
regarding their mechanical reliability and their operation, especially if their
structure is provided in plastics, for example, instead of the usual metallic
The traditional bow compasses are also rather heavy in order to ensure
a sturdy structure for a precise operation.
The aim of the present invention is that of providing a compass for
draughtsmen, particularly a bow compass, that, owing to a particular geometrical
configuration, eases the hand movement in the drawing and at the same time ensures
an absolute precision.
Within this aim, an object of the invention, is that of providing
a bow compass which is constructively simple and easy to use.
Another object of the invention is that of providing a bow compass
having low manufacturing costs.
A further object, is that of providing a compass with a new and likeable
The above aim, as well as these and other objects that will be more
apparent later, are achieved by a compass, particularly for draughtsmen, comprising
a first and a second rod element, said second rod element being hinged to said
first rod element at their upper ends, a point being associated with the lower
end of said first rod element, a fastening means for a drawing means being associated
with the lower end of said rod second element, a slider member having a first
end slidable in a first runner in said first rod element, characterized in that
said slider member has a second end slidable in a second runner, said second runner
being laid out in said second rod element, a screw element being associated with
said first rod element and being adapted to cooperate with a threaded bore of said
slider such that to a rotation of said screw element corresponds an axial shift
of said slider.
Further characteristics and advantages of the invention will be more
apparent by the following description of a preferred embodiment of the invention,
illustrated, by way of example in the enclosed drawings in which:
- Fig. 1 is an isometric view of a bow compass according to the invention;
- Fig. 2 is a side elevated view of the bow compass;
- Fig. 3 is a sectioned side view of the bow compass;
- Fig. 4 is an isometric view of the slider element;
- Fig. 5 and 6 are side elevated view of the bow compass, respectively in the
closed position and in a partially open position;
- Fig. 7 is partially sectioned side elevated view of the bow compass.
With reference to the above figures, a draughtsman compass 1 will
be described, of the type usually called bow compass, adapted to draw circles of
The bow compass 1 comprises a first rod element 2 hinged to a second
rod element 3 by means of an upper head 4.
The lower end of the first rod element 2 has a point 5, while the
lower end of the second rod element 3 has a fastening means 6 for drawing means
such as, for example, a lead holder or a drawing pen, not illustrated in the drawings
On the first rod element 2, a first runner is provided by means of
two rectilinear grooves 7, on opposite sides of the first rod element, parallely
laid out on the axis of the same first rod element.
A second runner is formed on the second rod element 3 and is provided
by means of two grooves 8, again on opposite sides of the second rod element, slanted
of a set angle relatively to the axis of the second rod element.
The runners of the first and second rod elements are engaged by the
ends of a slider element 9 comprising a core 10 and two plates 11 provided with
pins 12 adapted to slide in the grooves 7 and 8.
A threaded bore 13 is provided in the core 10 and is engaged by a
screw element 14 supported on the first rod element 2.
As better shown in Fig. 7, the screw element 14 is substantially
at the axis of the first rod element 2 and is inserted upwardly in the hand grip
15 of the bow compass.
A knob 16 is fastened on the upper end of the screw element to manually
rotate the screw element itself.
The operation of the bow compass is very simple, it is in fact sufficient
to rotate the knob 16 for axially displacing the slider 9 causing the two rod elements
2 ,3 to open or close, adjusting the aperture of the compass, because of the relative
configuration of the grooves 7 and 8.
It has been practically observed how the invention achieves the intended
aim and objects by providing a bow compass of great mechanical precision and at
the same time of easy use; an advantage of the invention is that of the hand grip
which is provided on the axis of rotation of the bow compass itself and which comprises
also the aperture adjusting knob.
Another advantage of the particular structure of the bow compass
according to the invention is that of allowing the use of different materials still
keeping a remarkable mechanical reliability.
The materials employed, as well as the dimensions, may be any according
to the specific needs and the state of the art.
Where technical features mentioned in any claim are followed by reference
signs, those reference signs have been included for the sole purpose of increasing
the intelligibility of the claims and accordingly, such reference signs do not
have any limiting effect on the scope of each element identified by way of example
by such reference signs.