GB2327910A

GB2327910A - Drawing or cutting instrument for circles or circular arcs

Info

Publication number: GB2327910A
Application number: GB9716069A
Authority: GB
Inventors: Ahmed Abdel Rahman Elagib
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-07-31
Filing date: 1997-07-31
Publication date: 1999-02-10
Also published as: GB9716069D0

Abstract

The device comprises an axle 12 with larger and smaller wheels 10,11 of diameters D,d respectively spaced on the axle and rotatable thereon, and a marker device 14 carried by the axle between the two wheels. The wheels are replaceable, allowing the radius of the circular arc to be changed by varying the diameter of the two wheels or the position of the marker between the wheels.

Description

TITLE: DIFFERENTIAL COMPASS DESCRIPTION The specification describes a differential compass.

Such an instrument may be used for drawing, cutting or marking continuous circles or arcs without the need to mark or fix part of the device at a centre point.

The device comprises, as can be seen from the accompanying figures, two sharp rimmed wheels 10 and 11 of diameter d and D respectively which are fixed on the axle 12. A pencil, cutter or marker holder 13 is mounted on the axle 12 between the wheels. The holder 13 may pivot freely in a plane normal to the axis of the axle 12. In use a pencil, cutter or marker 14 is mounted in the holder 13 between the two wheels 10 and 11.

When the instrument is pushed by a finger or pulled by a draw-bar it will run round a centre point. The radius of the circle traced by the pencil, cutter or marker 14 may be defined in terms of the radii of the circular paths traced by the wheels 10 and 11.

For example the market 14 will trace a circle the radius of which is equal to the radius of the circle traversed by the smaller wheel 10 plus the distance between the point at which the marker 14 meets the paper and the point at which the rim of the wheel 10 meets the paper, alternatively the marker may be said to have a path the radius of which is less than the radius of the circle traced by the larger wheel by an amount equal to the distance between the points at which they both meet the paper.

The radii of the circular paths traversed by the wheels 10 and 11 may be determined without reference to the common centre point of the paths.

The radii of the path traced by the smaller wheel for example is given by the expression Rd Xd (where d and D respectively are the diameters D-d of the wheels 10 and 11 and X is the distance on the surface being marked between the points at which the two wheels touch that surface).

The paths traversed by the large wheel 11 can be expressed as RD= XD D-d It will therefore be seen that a circular path may be marked onto a surface without reference to a centre point making use of the differential compass described above. The radius of the circular path marked being determined independently of the centre point and in terms of the dimensions of the instrument itself.

It will be seen that the radius of the marked circle to be drawn on the surface may be varied, for example by variation of the axial spacing of the wheels 10 and 11 (thereby varying the dimension X) or by substituting one or both of the wheels 10 and 11 with other wheels of different relative dimensions.

Claims

1. A differential compass for forming a perfect circular marking or cuttings on material said compass comprising an axle supporting two rotatable wheels and also a marker or cutter engageable with a surface for marking when the differential compass is positional for use, the wheels being of different diameter so that the compass moves through an arcuate path when pushed such that the path defines a perfect circle, portion of a circle or curve.

2. A differential compass as claimed in claim 1, wherein the marker is located on the axle between the wheels.

3. A differential compass as claimed in claim 1 or 2, wherein position djusting means are provided for the marker to enable the marker to be positioned selectively on the axle.

4. A differential compass as claimed in any one of the preceding claims, wherein means are provided enabling at least one of the wheels to be positioned selectively on the axle.

5. A differential compass as claimed in any one of the preceding claims, wherein one or both of the wheels are removable whereby said wheel can be substituted with other wheels to provide a different diameter differential.

6. A differential compass as claimed in any one of the preceding claims, wherein the surface engaging peripheral edges of the wheels are relatively sharp.

7. A differential compass as claimed in claim 3, wherein means are provided to enable selective swinging of the marker about the axle.

8. A differential compass as claimed in any one of the preceding claims, wherein one or both of the wheels are removable whereby wheels having a different diameter differential can be fitted on the axle.

9. A differential compass substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings