GB2301799A - Drawing aid using dividers or calipers - Google Patents

Abstract

A drawing aid (1) comprises a dividers or calipers having two arms (2, 3) pivoted together (4) at one end of each arm so that the free ends (7) of the arms (2, 3) may be located at any required arcuate spacing from one another. Each arm (2, 3) is provided with a series of markings (6)spaced along the arm. Respective corresponding markings (6) are provided on each arm at the same radius. The markings are located so that spacing between corresponding markings (6) at the same radius on each arm (2, 3) represents a predetermined and identified fraction of the spacing between the tips (7) of the ends of the arms for any arcuate position of the arms, applications include scaling up or down and the establishment of perspective in drawings.

Description

"FREEHAND DRAWING AID" The invention relates to a freehand drawing aid especially for use by artists and draughtsmen requiring to prepare freehand sketches. In particular, the invention relates to a calibrated scaling calipers or dividers for artists' use.

The accurate depiction to a reduced scale in a freehand drawing of a physical object or scene can be a difficult process, especially for the inexperienced artist or draughtsman, requiring either the use of rulers or the like or the availability of a very high degree of experience and skill on the part of the artist or draughtsman. It is known to prepare full size drawings of objects and reduce these to a lesser scale by means of a pantograph, but this method does not lend itself to the accurate scaling of full size scenes, unless these are first recorded in a photograph. It is also known to reduce completed drawings using photographic means, such as a reducing or enlarging photocopier, but this frequently tends to produce distortion, especially at the edges of a drawing.

It is an object of the invention to provide an especially convenient apparatus and method for enabling an artist or draughtsman to rapidly reduce or enlarge the scale of reproduction of a physical article or scene in a freehand drawing.

According to the invention there is provided a freehand drawing aid comprising a dividers or calipers having two arms pivoted together at one end of each arm so that the free ends of the arms may be located at any required arcuate spacing from one another, wherein each arm is provided with a series of markings spaced along the arm, respective corresponding markings being provided on each arm at the same radius, and the markings being located so that the spacing between corresponding markings at the same radius on each arm represents a predetermined and identified fraction of the spacing between the tips or free ends of the arms for any arcuate position of the arms.

The arms are suitably provided with ten sets of corresponding markings to provide for a series of ratios for the spacing between corresponding markings at the same radius on each arm and the spacing between the tips or free ends of the arms in the range 1.5:1 to 8:1.

The cross-section of each arm may be such as to provide a bevelled edge on the arm on the side of the arm directed towards the other arm in use of the drawing aid so as to facilitate positioning and adjustment of the arms so that the spacing between two corresponding markings on the arms or between the tips of the arms may accurately represent a distance to be scaled in a view or on a drawing.

At least one arm may comprise a radially slideable pointer positionable at any required radial location along the arm, for alignment with a particular marking on the arm as a reminder of the selected scaling ratio currently in use, or for placement between markings along the arm in order to apply a non-predetermined scaling ratio. Suitably each arm comprises a said pointer.

The arms are suitably pivoted together in such a manner as to provide sufficient friction for the arms to remain at a predetermined angle relative to one another following adjustment or positioning of the arms in use of the drawing aid.

The invention also extends to a freehand drawing aid substantially as described herein with reference to the accompanying drawings or as shown in Figure 1, or in Figure 1 as modified by Figure 5 or Figure 6.

While the drawing aid or device of the invention is infinitely variable, up to ten calibrations are suitably provided for specific fractional spacings. The markings may suitably provide for fractional spacings for divisors of 1.5, 2i 2.5. 3, 3.5, 4, 5, 6, 7 and 8. Thus these scale calibrations provide for ratios between the arm spacing at the radius of the markings and the arm spacing at the tips of the arms of 1.5:1, 2:1 and so on up to 8:1. Accordingly, if the tips of the arms are set at a spacing of for example 10 centimeters, the spacing between the corresponding markings on the two arms signifying a ratio of 2:1 will be 5 centimeters. Similarly, the spacing between the corresponding markings signifying a ratio of 4:1 will be 2.5 centimeters. Spacing can mean either linear or arcuate spacing.

The pivot arrangement for the arms of the unit is suitably such as to provide for frictional retention of the arms in a particular pivotal orientation against inadvertent displacement, the frictional force being however capable of being readily overcome by manual action to displace the arms into a new arcuate disposition, as required.

In use of the device of the invention, the arms of the dividers or calipers are spaced apart so that the spacing between a corresponding pair of ratio markings on the arms corresponds to the spacing between two particular points on an object or in a scene to be represented as viewed by the user when the dividers is held at a specified distance, for example, arm's length, from the user's eye.

The spacing between the tips of the dividers may then be used to represent this spacing to an enlarged scale on a drawing. Thus according to the invention, a selected pair of corresponding markings on the two divider arms are used to identify a "real" distance which is a sub-multiple of the spacing between the tips, and this distance is then represented in the drawing of the article or scene as an appropriately enlarged dimension. An inversion of this procedure similarly allows a dimension to be reduced.

The device of the invention may also be used to establish a perspective angle in a drawing or representation by holding one of the arms in alignment with a first perspective line or plane identified in a scene, which may for example be a vertical disposition of the arm and adjusting the pivoting of the other arm until it corresponds to another perspective line or plane as identified in the scene.

An embodiment of the invention will now be described having regard to the accompanying drawings, in which Figure 1 is a plan view of a unit according to the invention, Figure 2 is a diagrammatic representation of the unit of the invention in use for scaling a physical article, Figure 3 is a diagrammatic representation of the unit of the invention applied to establishing a perspective structure for representing a scene in a freehand sketch, Figure 4 shows use of the device of the invention for scaling reproduction from a photograph or drawing, Figure 5 shows a variant of the device of the invention as shown in Figure 1, in which a slider or pointer is provided on each arm of the calipers, as a memory aid in use of a particular scaling ratio, or to allow an interpolated and non-predetermined scaling ratio to be used, and Figure 6 shows end views of the arms of the device in cross-section, showing a bevelled cross-section especially suitable for precision in measurement.

As shown in Figure 1, a freehand drawing aid 1 according to the invention provides a dividers or calipers having two arms 2, 3 pivoted 4 to one another at one end, the arms being held together by a screw or bolt arrangement providing a degree of friction between the pivoted ends such as to retain the arms in a particular pivoted disposition against inadvertent displacement, but which frictional retention can be overcome by manual action to move the arms to a new disposition as required. Each arm 2, 3 has an overlapping and rebated end portion 5 for matching pivotal engagement with the other arm 3, 2. Each arm 2, 3 is provided along its length with a series of ten markings 6.Matching markings 6 are provided on each arm 2, 3, such that when the two arms 2, 3 are pivoted together to abut one another, respective markings 6 on each arm 2, 3 are at the same radial distance along each arm 2, 3 from the axis of pivoting 4 of the arms 2, 3. The spacings of the markings 6 from the free ends or tips 7 of the arms 2, 3 are selected so that when the arms 2, 3 are pivoted apart, as shown in the drawing, each of a pair of markings 6 on one arm 2 is at a linear or arcuate spacing from the corresponding marking 6 on the other arm 3, which spacing is a specified sub-multiple of the spacing between the tips 7 of the arms 2, 3. Thus for example, as shown in the drawing, the markings 6 identified as "2" are spaced from the tips 7 of the arms 2, 3 such that the distance between these two markings 6 is exactly one-half of the distance between the tips 7 of the arms 2, 3.

Similarly for the markings 6 identified as "3", the spacing is one-third, and so on for the markings 6 identified as "4" and "5", one-quarter and one-fifth respectively. The same applies for further markings down to the 8:1 ratio. It will be appreciated that when the device is used to scale up or down by higher factors, such as 6, 7 or 8, the possibility of error is increased, but this may readily be overcome and accurate scaling achieved by using a larger version of the device of the invention for accurate scaling at these high reduction or magnification ratios.

Thus by pivoting the arms 2, 3 apart until the spacing between the particular marks 6, for example, at the 2:1 ratio, corresponds to a specified distance, which may be a physical distance between points on an object or which may be a distance established in a scene being viewed by an artist or draughtsman through the open dividers held at arm's length, a larger spacing substantially true to scale may be transferred to paper, by scaling the distance between the tips of the divider arms 2, 3 on the paper or other sketching medium.

One manner of use of the invention is shown in the diagrammatic sketch of Figure 2, where an artist's eye 11 is shown evaluating the diameter 12 at the upper end of a vase or bowl 13, which it is required to draw on paper. In this instance, the dividers 1 is placed between the viewer's eye 11 and the object 13, with the dividers 1 being held at arm's length or another specified and constant distance from the artist's eye 11, and the spacing of the arms 2, 3 is adjusted until the spacing through the dividers between the arms at a selected calibration, for example 2:1, corresponds to the diameter 12 of the object 13, as seen by the artist. An enlarged value corresponding to this distance may then be transferred to paper by setting out or marking on the sheet of paper on which the drawing is to be prepared a distance corresponding to the spacing between the tips 7 of the arms.

This spacing equates to twice the dimension measured between the 2:1 calibration points on the arms of the device. Other dimensions on the article 13 may be similarly scaled, in each instance the dividers 1 being held at substantially the same distance from the artist's eye 11 as for the first measurement recorded.

It will be immediately appreciated that for relatively small articles, the dividers 1 may alternatively be applied directly to the article 13, in much the same manner as a conventional calipers. In other words, if the bowl or unit 13 to be sketched is quite small, the dividers 1 may be placed directly across its upper diameter 12 and then subsequently across other dimensions of the object 13. It may also be applied to the measurement of object height, in each case with appropriate scaling as is required.

It will be further appreciated that the dividers 1 may also be applied to reducing an object, where something of relatively large dimensions but at close quarters is in question. In this instance, the scaling is effected so that the dimension to be reduced is measured between the tips of the divider arms 2, 3, and this distance is then reduced on the drawing by setting out a distance on paper corresponding to for example the spacing between the points for the ratio 2:1 on the divider arms 2, 3.

It will be still further appreciated that the device 1 may be applied to a very wide angular range of tip 7 spacings, for example up 0 to 135 or more, but it will also be observed that the device 1 will be found most useful within the acute angle range less than 900, where the measurements are relatively more straightforward. Use of the device 1 within this angular range can readily be effected, even where wide objects are in question, by suitably selecting the position of the dividers 1 between the artist's eye 11 and the object or scene, as can be appreciated from Figure 2 of the drawings.

The device of the invention is further useful in appraising a perspective line to be recorded in a drawing, as shown in Figure 3.

In this instance, the device 1 of the invention is placed between the artist's eye and the scene to be recorded. One arm 2 of the dividers 1 is set to be aligned with one boundary line or feature 21 of the scene in perspective view, which may be a vertical line or feature, as shown in Figure 3, but is not necessarily vertical, and the angle of the other arm 3 relative to the arm 2 is adjusted until it corresponds to a further perspective line 22 as seen by the eye 23 for a further boundary line or feature, for example, of an object 23 of the scene having also the first or vertical line 21. The dividers 1 may then be used to establish a perspective structure on paper, which will enable the artist to rapidly progress a perspective drawing of high quality.

Figure 4 shows an application of the device of the invention to direct scaling from a photograph or drawing to prepare a sketch of the subject matter in question. In this instance, the dividers 1 may be laid on the photograph or drawing 31 so that for example a selected pair of corresponding calibrations on the two arms, such as those for the 2:1 ratio, correspond to a particular dimension on the photograph or drawing. An enlarged measurement 32 corresponding to this dimension, for example doubled in the particular case shown in the drawing, may then be set out on the sketch of drawing to be prepared at the tips of the arms.This may be achieved in a direct manner by the sheet of paper on which the drawing is to be prepared being located immediately adjacent to the photograph or drawing 31, so that the dimension 32 may be recorded while the device is actually in position on the photograph or drawing, or alternatively, the dimension, reference 33, may be measured on the photograph or drawing and then transferred to the paper on which the new sketch or drawing is to be prepared. Perspective angles make likewise be incorporated in the new sketch or drawing by use of the device in the manner already described with respect to Figure 3.

Figure 5 shows a modification of the invention in which each arm 2, 3 of the dividers 1 of Figure 1 is provided with a pointer or slider 41, mounted on the arm for sliding movement, such as in clip-on manner, or alternatively by engagement in a groove extending radially along the arm, so that the pointer 41 may be positioned at substantially any required position along the longitudinal extent of the respective arm 2 or 3. In use of the device of the invention, the pointer 41 may be positioned at a particular ratio mark along the length of the arm, to act as a reminder or "aide memoire" for the user, so as to assist the user in recalling which particular ratio is currently in use. This gets over the problem which may arise when a user is making a succession of measurements, and is possibly interrupted in use of the invention and sets it aside for a period before returning to the work. The slider or pointer may be further used to interpolate between specific markings, such as for example between the 1.5:1 and 2:1 ratios as shown in the drawing, where for example a reduction or increase of approximately 2.25 might be in question.

The accuracy of use of the device of the invention may be further enhanced by the cross-sectional arrangement of the arms 2, 3 shown in Figure 6, which results in the inner edges 51 of the arms, namely those which face towards one another, being bevelled. Thus each arm tapers in reducing cross-section manner towards its inward edge 51. This bevelled region may have substantially the cross-section of a quarter circle, or any other suitable tapering or reducing profile. In this manner, there is a defined relatively sharp edge 51 along the inner side of each arm, thereby enabling the corresponding markings on each arm to be aligned accurately and positively with a distance or dimension to be assessed in use of the device of the invention.

In the upper part of Figure 6, the bevelled arms are shown spaced apart. In the lower part of Figure 6, the bevelled arms are shown brought together, so that the tapering or relatively sharp edges abut. The markings on the arms are preferably carried through to these well defined edges, so as to provide a precise locating point on each arm for alignment with the dimension to be measured, without any error being introduced due to the thickness of the arm at the location of the marking.

Claims (7)

1. A freehand drawing aid comprising a dividers or calipers having two arms pivoted together at one end of each arm so that the free ends of the arms may be located at any required arcuate spacing from one another, wherein each arm is provided with a series of markings spaced along the arm, respective corresponding markings being provided on each arm at the same radius, and the markings being located so that the spacing between corresponding markings at the same radius on each arm represents a predetermined and identified fraction of the spacing between the tips or free ends of the arms for any arcuate position of the arms.

2. A freehand drawing aid according to Claim 1, wherein the arms are provided with ten sets of corresponding markings to provide for a series of ratios for the spacing between corresponding markings at the same radius on each arm and the spacing between the tips or free ends of the arms in the range 1.5:1 to 8:1.

3. A freehand drawing aid according to Claim 1 or Claim 2, wherein the cross-section of each arm is such as to provide a bevelled edge on the arm on the side of the arm directed towards the other arm in use of the drawing aid so as to facilitate positioning and adjustment of the arms so that the spacing between two corresponding markings on the arms or between the tips of the arms may accurately represent a distance to be scaled in a view or on a drawing.

4. A freehand drawing aid according to any preceding claim, wherein at least one arm comprises a radially slideable pointer positionable at any required radial location along the arm, for alignment with a particular marking on the arm as a reminder of the selected scaling ratio currently in use, or for placement between markings along the arm in order to apply a non-predetermined scaling ratio.

5. A freehand drawing aid according to Claim 4, wherein each arm comprises a said pointer.

6. A freehand drawing aid according to any preceding claim, wherein the arms are pivoted together in such a manner as to provide sufficient friction for the arms to remain at a predetermined angle relative to one another following adjustment or positioning of the arms in use of the drawing aid.

7. A freehand drawing aid substantially as described herein with reference to the accompanying drawings or as shown in Figure 1, or in Figure 1 as modified by Figure 5 or Figure 6.