GB2232125A

GB2232125A - Drawing aid for determining a mid-point

Info

Publication number: GB2232125A
Application number: GB8912833A
Authority: GB
Inventors: Philip J Schatzberger
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-06-03
Filing date: 1989-06-03
Publication date: 1990-12-05
Also published as: GB8912833D0

Abstract

A drawing aid in the form of a compass or divider includes a third, central leg (16, 56) for determining the mid-point between two positions. The outer legs (12, 14, 52, 54) are movable with respect to the third leg so that the third leg constantly bisects the angle between the outer legs. <IMAGE>

Description

DRAWING AID This invention relates to a drawing aid.

In drawing applications, it is quite common for the draughtsman to wish to find the mid-point between two positions. There are a number of known methods of achieving this. The most basic technique involves measuring the distance between the two positions, calculating the midpoint, then measuring the mid-point. This task can be made a little easier with a device known as a "centering ruler It is an object of the present, invented to provide an improved means of finding the mid-point between the two positions.

According to one aspect of the present invention, there is provided a drawing aid comprising a first elongate leg, having at one end thereof a point adapted to engage a surface, a second elongate leg, having at one end thereof a point adapted to engage the surface, and a third elongate leg disposed between the first and second legs and also having a point adapted to engage the surface, wherein the first and second legs are moveable with respect to one another, and the arrangement is such that ratio of the distance between the point of the first leg and the point of the third leg to the distance between the point of the second leg and the point of the third leg is substantially constant.

The drawing aid can be in the form of a divider (also known as a bow), or in the form of a compass in which each one of the points may be formed by a pencil lead.

Advantageously, the distance between the point of the first leg and the point of the third leg is substantially equal to the distance between the point of the second leg and the point of the first leg. This enables the third leg to indicate the mid-point between the first and second legs.

Preferably, the first leg is pivotally movable with respect to the second leg. More preferably, the first and second legs are pivotally connected at or adjacent to an end thereof remote from the point engaging the surface.

The relative movement of the first and second legs may be controlled by a gearing arrangement in a known manner. For example, in one embodiment the first and second members may be pivotally connected by gear wheels; in another embodiment, the first and second members may be provided with a screwthreaded member extending therethrough such that rotation of the screwthreaded member causes movement of the first and second legs.

Advantageously, at least part of the third leg is adapted for movement along its longitudinal axis. This enables the third member to be moved into and out of contact with the surface.

In one construction, the third leg may be moveable as an integral unit; in another construction, only the lower part of the third leg is moveable; the lower part may be removable from the rest of the third leg.

Preferably, the third leg is biased to a position in which its point does not engage the surface when the points of the second and third members engage the surface.

According to another aspect of the invention, there is provided a drawing aid comprising a first elongate leg having at one end thereof a point adapted to engage a surface, a second elongate leg having at one end thereof a point adapted to engage the surface, said first and second members being pivotally secured at a position remote from the points of the first and second legs, and a third elongate leg having at one end thereof a point adapted to engage the surface, wherein the third leg is adapted to bisect the angle between the first and second legs.

The drawing aid, according to the invention, can be used in any drawing application. For instance, it can be used in the preparation of engineering drawings, or the preparation of artwork for printing.

Reference is now made to the accompanying drawings, in which: Figure 1 is a side elevation of one embodiment of a drawing aid according to the invention; and Figure 2 is a side elevation of another embodiment of a drawing aid according to the invention.

Referring to Figure 1, a drawing aid in the form of a bow, generally designated 10 comprises a first leg 12, a second leg 14, and a third leg 16 intermediate the first and second legs 12 and 14.

The legs 12, 14 and 16 are each provided with a point 18, 20 and 22 respectively, at their lower ends; the points 18, 20 and 22 are defined by pin-like members 24, 26 and 28 respectively.

The ends of the legs 12 and 14 remote from the points 18 and 20 are pivotally connected within a housing 30. The legs 12 and 14 are pivotally moveable in relation to the housing 30, whilst the third leg 16 is fixedly secured to the housing 30; if desired, the third leg 16 can be integral with the housing 30.

A threaded spindle 32 extends through the legs 12, 14 and 16. A wheel 34 is rotatably mounted on the spindle and is held in a fixed axial position relative to the spindle 32, within a recess 36 in the housing 30, and the third leg 16. Rotation of the wheel 34 in one direction causes the legs 12 and 14 to move apart, whilst rotation of the wheel 34 in the opposite direction causes the legs 12 and 14 to move together. This action is conventional and well known in the construction of bows.

The longitudinal axis of the leg 16, passing through the point 22, is substantially parallel to and coincident with the plane of the wheel 34.

During rotation of the wheel 34, the leg 16 remains substantially equidistant from the legs 12 and 14. Thus, the point 22 remains substantially equidistant from the points 18 and 20.

The pin-like member 28 is secured to the lower end of a moveable member 38, which is slideable within a retaining housing 40. The member 38 is spring biased towards an upper position, as shown in the drawing.

A slot 42 is provided in the retaining housing 40; an operating member 44 is connected to the moveable member 38, and projects through the slot 42, so that the application of downward pressure to the operating member 38 causes downward movement of the point 22.

The bow 10 is used as follows: The points 18 and 20 are placed on the surface (not shown), each in a respective one of two preselected positions. The operating member 44 is then pushed downwardly, to engage and mark the surface. In this way, a position mid-way between the two positions can be identified.

The embodiment of drawing aid shown in figure 2 comprises a bow generally designated 50, which comprises first, second and third elongate legs 52, 54 and 56 respectively.

The legs 52 and 54 have respective points 58 and 60 at one end thereof, and are very similar to the legs 12 and 14 shown in figure 1.

The legs 52 and 54 are pivotally connected to one another, inside a housing 62. The legs 52 and 54 are connected through a gear arrangement (not shown); this type of arrangement is conventional and well known.

The third leg 56 has a point 64, which is also capable of engaging the surface. The third leg 56 is moveable, as a whole, towards and away from the surface, in a direction which is substantially parallel to its longitudinal axis The end of the leg 56 remote from the point 64 is provided with a retaining member 66 which acts to retain a biasing spring 68. The biasing spring 68 is disposed between the retaining member 66 and an upper surface 62a of the housing 62. The biasing spring 68 serves to bias the leg 56 upwardly to a position which would normally be out of contact with the surface.

The bow 50 is used in a similar manner to the bow 10. The principle difference is that the point 64 of the third leg 56 is moved into engagement with the surface by pressing the retaining member 66 downward.

It will be appreciated that the drawing aid described above may be modified within the scope of the invention. For example, the third leg can be manufactured as a seperate part for attachment to existing drawing aids.

Claims

1. A drawing aid comprising a first elongate leg, having at one end thereof a point adapted to engage a surface, a second elongate leg, having at one end thereof a point adapted to engage the surface, and a third elongate leg disposed between the first and second legs and also having a point adapted to engage the surface, wherein the first and second legs are movable with respect to one another, and the arrangement is such that ratio of the distance between the point of the first leg and the point of the third leg to the distance between the point of the second leg and the point of the third leg is substantially constant.

2. A drawing aid according to Claim 1, wherein the distance between the point of the first leg and the point of the third leg is substantially equal to the distance between the point of the second leg and the point of the first leg.

3. A drawing aid according to Claim 1 or 2, wherein the first leg is pivotally movable with respect to the second leg.

4. A drawing aid according to any preceding claim, wherein the first and second legs are pivotally connected at or adjacent to an end thereof remote from the point engaging the surface.

5. A drawing aid according to any preceding claim, wherein the first and second members are pivotally connected by gear wheels.

6. A drawing aid according to any preceding claim, wherein the first and second members may be provided with a screwthreaded member extending therethrough such that rotation of the screwthreaded member causes movement of the first and second legs.

7. A drawing aid according to any preceding claim, wherein at least part of the third leg is adapted for movement along its longitudinal axis.

8. A drawing aid according to any preceding claim, wherein the third leg is movable as an integral unit.

9. A drawing aid according to any of Claims 1 to 7, wherein only the lower part of the third leg is movable; the lower part being removable from the rest of the third leg.

10. A drawing aid according to any preceding claim, wherein the third leg is biased to a position in which its point does not engage the surface when the points of the second and third members engage the surface.

11. A drawing aid comprising a first elongate leg having at one end thereof a point adapted to engage a surface, a second elongate leg having at one end thereof a point adapted to engage the surface, said first and second members being pivotally secured at a position remote from the points of the first and second legs, and a third elongate leg having at one end thereof a point adapted to engage the surface, wherein the third leg is adapted to bisect the angle between the first and second legs.