GB2202493A - Curve drawing apparatus - Google Patents

Abstract

Curve drawing apparatus comprises a base member, conveniently an aluminium extrusion (1), with two mounting members (2,3) variably positioned thereon. A resilient wire or strip (4) extends between the mounting members, the curve being drawn along the wire or strip. The position and curvature of the strip are varied by varying the positions of the mounting members and the angle of the wire or strip relative to the mounting members. In accordance with the invention, variation of the angle is affected using a high mechanical advantage connection, e.g. a worm gear. <IMAGE>

Description

Curve Drawing Apparatus This invention relates to curve drawing apparatus.

Most artists and draughtsmen do not have the ability to draw free-hand an accurate and even curve. Accordingly apparatus has been developed over the centuries to assist artists in doing so. The simplest such apparatus is the compass, but this suffers from the disadvantage that it can only draw arcs of circles. Various apparatus has been proposed and some commercialised for drawing curves which are not arcs of circles, and various types are available commercially.

Two types may be distinguished: those which provide a selection of fixed curves, one of which needs to be used by the artist, and those which have some sort of variable curvature mechanism. A common feature to both types is the provision of a curved edge along which a drawing implement such as a pencil may be moved to draw a desired line.

A number of devices have been proposed which use a resilient member held on a frame and which can be deformed to a particular curve shape. Currently available under the trade mark Acu-Arc is a piece of apparatus consisting of a resilient bendable member and a rigid ruler, pivoted together at one end. The non-pivoted end of the resilient member may be fixed in position on the ruler over a range of positions corresponding to the resilient member being straight and, as the fixture point is moved towards the pivot, bending with a decreasing radius of curvature. The range of radii of curvature achievable with such a system is limited, and the device is only useful for drawing circular curves.

Swiss Patent Specification 142472 discloses a system consisting of a rigid bar and a resilient strip. The resilient strip is held to the bar at two spaced points by clamping systems enabling the strip to be fixed at an angle to the bar. By adjusting the spacing of the two fixing points and the angles relative to the bar at the two fixing points, the strip may be made to take up a variety of curved configurations. Such apparatus is fairly inconvenient to use. German Patent Specifications 29818 and 76099 disclose similar systems involving the use of a resilient metal wire or strip variably clamped to a straight, L-shaped or angled rigid base. These devices suffer from a lack of ease of manipulation, and in particular from a lack of reproducibility. It is not possible easily to reset a curve previously drawn if that is desired.

Mention should also be made of ruler strips consisting of a deformable centre member and an external plastics sheath. These may be deformed over a certain range of curvature to provide a bent plastics edge against which a line may be drawn. Because of the lack of resilience, the production of evenly graded curves using such apparatus is difficult.

We have now found that much improved curve drawing apparatus may be constructed, using a resilient wire or strip as the deformable element which is formed to a curve shape and against which a curve is then drawn, if the element is mounted on a rigid base by mechanisms enabling its angle to be easily adjusted relative to the base but which do not require clamping to maintain that angle.

In accordance with the present invention there is provided apparatus for drawing curves comprising a base member, two mounting units each adapted to be attached to the base member and positioned variably thereon, and each mounting member having means to grip a resilient curvable member, and including means providing a high mechanical advantage enabling the angle between the resilient curvable member and the mounting member to be varied.

Such apparatus may be simply constructed. Using a high mechanical advantage connection, it may be easily achieved that the angle of the resilient member with respect to the mounting can be changed with ease, e.g. by turning a knob, but that the reaction force of the resilient member on the mounting member will be insufficient to turn it relative to the mounting member.

The preferred high mechanical advantage system is that of a worm gear. In a worm gear, a toothed wheel is turned with the aid of a worm having an external helical thread which engages on the outside of the wheel. The wheel may easily be turned by turning the worm about its axis, but attempts to turn the wheel about its axis do not cause the worm to turn.

A major advantage of such a system is that no locking or clamping means is necessary to hold the resilient member in a given angle relative to the mounting. The mechanical advantage of the worm gear simply holds the wheel in the desired position.

The rigid base is preferably a simple rod or bar on which the mounting members are slidably mounted. Means such as a simple clamping screw are preferably provided in order to enable the distance between the two mounting means to be fixed by clamping both mounting means to the rigid base.

Preferably the resilient member is a wire, though resilient strips may also be used. Preferably the ends of the resilient wire or strip are easily detachable from a connection with the mounting to enable strips of different resilience or different lengths to be used.

The invention is illustrated by way of example with reference to the accompanying drawings in which, Figure 1 is a perspective view of apparatus in accordance with the invention, and Figure 2 is an under-plan view of one of the mounting members.

Referring to the drawings the apparatus comprises an extruded aluminium strip 1 which acts as the base and on which are slidably mounted two carriages 2 and 3. Between the two carriages is a resilient wire 4 having mounting blocks 5,6 on its ends.

Strip 1 is formed with a T-section groove 7 into which is fitted a block 8 having four bearer pads 9 on it, each of which engages under one of the lips of the groove 7. Bearer pad 8 is fixed in a housing 10 of one of the mountings 2,3. A clamping screw 12 is set in each mounting and is actuatable by a knurled head 13 which projects from the top of the housing 10.

Mounted in the housing 10 is a shaft 15 bearing a worm 16 and, externally of the housing, a knurled actuation knob 17 enabling the worm to be turned.

The worm engages with an outer pinion 19 of a disc mounted for rotation in housing 10. The disc has a depending skirt 20 and a pair of slots in the skirt receive an elongate tang 22 which is integral with mounting 6 or 5.

The lower edge of skirt 20, as seen in Figure 1, is positioned closely adjacent a flat surface e.g. a sheet of drawing paper on which the apparatus as shown Figure 1 rests. There is a hole in the end of tang 22 through which a bent portion 24 of a retaining spring 25 located internally of skirt 20 protrudes, in order releasably to hold tang 22 in place.

Fixed on the disc mounted on casing 10 and visible from above is a graduated disc 27 and the upper surface of housing 10 bears a reference mark 28.

It can be seen from Figure 2 that if actuation knob 17 is rotated, worm 16 turns and this will turn the pinion 19 and skirt 20, thus changing the angle which tang 22 makes with shaft 15. When the mounting is mounted on base 1 as shown in Figure 1, the angle at which the resilient wire 4 is set relative to the mounting 2 or 3 may accordingly be changed. It is easy to turn knob 17 by hand and set the desired angle. However, because of the mechanical advantage of the worm gear, once set the angle does not change until knob 17 is turned again.

By setting the spacing of mountings 2 and 3 and adjusting the angles of tangs 22 with respect to their mountings, resilient wire 4 may take up a variety of shapes. When the desired shape is achieved, a curved line corresponding thereto may be drawn by simply drawing a pencil or like writing implement along the edge of resilient member 4.

A particular advantage of the construction shown is that setting may take place with one or both clamping screws slackened off, one or both carriages 2 and 3 then simply sliding along strip 1 as the angle of the tang in the carriage is adjusted. Once the desired curve is achieved, the clamping screws are turned to fix the carriages in position. Adjustment is thus very rapidly and easily effected.

Member 1 may bear suitable graduations e.g. a centimetric scale along it, and mountings 2 and 3 may bear a suitable reference mark on them thus enabling a curve to be reproduced provided that the separation of mountings 2 and 3 and the readings on discs 27 relative to marks 28 are noted down for each mounting.

In order to enable a wider range of curves to be generated, the resilient member 4 and its associated mounting ends and tangs may be simply removed and replaced by one of different resilience e.g. with a thicker or thinner wire between members 5 and 6.

Claims (7)

1. Apparatus for drawing curves comprising a base member, two mounting units each adapted to be attached to the base member and positioned variably thereon, and each mounting member having means to grip a resilient curvable member, and including means providing a high mechanical advantage enabling the angle between the resilient curvable member and the mounting member to be varied.

2. Apparatus according to claim 1 wherein the high mechanical advantage system is a worm gear.

3. Apparatus according to claims 1 or 2 wherein the rigid base is an elongate member on which the mounting members are slidably mounted.

4. Apparatus according to any one of claims 1 to 3 and including clamping means on each mounting member to enable the distance between the two mounting means to be fixed by clamping both mounting means to the rigid base.

5. Apparatus according to any one of claims 1 to 4 wherein the resilient member is a wire.

6. Apparatus according to any one of claims 1 to 5 wherein the ends of the resilient member are detachably connected to the mounting members to enable resilient members of different resilience or different lengths to be used.

7. Apparatus for drawing curves substantially as hereinbefore described and illustrated with reference to the accompanying drawings.