GB2118105A - Drawing implements - Google Patents

Abstract

A drawing implement comprises a rigid, transparent ruler 10 on which is mounted a roller assembly 15 which engages the surface on which the implement rests and constrains the ruler to move linearly. The roller assembly 15 comprises two rollers 16, 17 mounted on a common shaft 18 which is frictionally engaged by a bar 21 which extends along the shaft and is connected to the ruler by screws 24, 25 so that by adjusting the screws the frictional restraint exerted on the roller assembly by the bar 21 may be varied. <IMAGE>

Description

SPECIFICATION Improvements in or relating to drawing implements The invention relates to a drawing implement, such as a ruler, set-square or protractor of the kind comprising an operative plate-like element and a roller assembly rotatably mounted on the element in a manner to engage the surface on which the element rests, the roller assembly rotating as the implement is moved over the surface so as to constrain the implement to move linearly.

Such an arrangement enables the drawing implement to be moved over a drawing board from one location to another without changing its attitude. This facilitates the drawing of parallel lines, for example, in the case where the plate-like element is a ruler, or allows angles to be transferred from one part of a drawing to another in the case where the element is a protractor.

A disadvantage of known implements of this type, however, is that they cannot be left on an inclined drawing board surface without rolling down the board under their own weight. In an effort to overcome this problem it has been proposed to provide the roller assembly with a brake mechanism which is normally engaged to prevent the assembly rotating, and which must be disengaged by the user, by pressing a button, when he wishes to move the implement over the drawing board. While such a construction is effective in ensuring that the implement does not roll down an inclined board when not being held by the user, it can be inconvenient to use and expensive to manufacture. In addition the brake mechanism may become less effective with time, due to wear of the component parts.

It is an object of the invention to provide a drawing implement in which these disadvantages are overcome and which, in particular permits the manufature of a simple and comparatively lowcost implement suitable for supply, for example, to school children.

According to the invention there is provided a drawing implement of the kind first referred to wherein there is mounted on the plate-like element a member which frictionally engages the roller assembly, or a part rotatable therewith, which member is adjustable with respect to the plate-like element in such a manner that said frictional engagement may be varied.

Thus, by adjustment of the member on the plate-like element the frictional engagement between the member and the roller assembly, or part rotatable therewith, may be adjusted so that the frictional restraint is just sufficient to prevent the implement rolling down an inclined drawing board, but may be readily overcome by the user to move the implement to a new position on the board. Since the member is adjustable, any wear of the components may be readily accommodated.

The roller assembly may comprise two rollers spaced apart on a common shaft, and adjustable member bearing frictionally against a portion of the shaft between the rollers. The shaft may be disposed on the upper side of the plate-like element, the rollers projecting through apertures in the element for engagement with the surface on which the implement rests. Preferably the peripheries of the rollers are ridged or otherwise formed to improve their frictional grip on the surface.

The adjustable member may be so mounted on the plate-like element as to extend cantileverfashion across the portion of the shaft, adjustable means, such as screws, being provided between the member and plate-like element whereby adjustment thereof flexes the member iXto frictional engagement with the shaft.

The adjustable member may be provided with means to locate the shaft on the plate-like element. For example, the side of the member facing the plate-like element may be formed with an elongate groove which partly embraces the shaft. The groove is preferably V-shaped in crosssection.

The plate-like element may comprise a ruler and/or protractor and is preferably formed from transparent rigid material.

The following is a detailed description, by way of example, of an embodiment of the invention, reference being made to the accompanying drawings in which: Figure 1 is a side elevation of a parallel rule in accordance with the invention, Figure 2 is a plan view of the ruler, Figure 3 is an end view of the ruler, and Figure 4 is an enlarged cross-section taken along the line X-X of Figure 2.

The plate-like part 10 of the ruler is formed from rigid transparent material such as transparent acrylic plastics sheet and is formed with parallel front and rear bevelled edges 11 and 12. The opposite end edges 13 and 14 of the ruler are also bevelled and are angled at 300. It may be marked with scales and/or with angles, according to its intended use.

A roller assembly 1 5 is mounted on the ruler and comprises two brass rollers 1 6 and 17, each having an axially ridged periphery, secured to opposite ends of a ground silver steel shaft 18.

The shaft 1 8 on the upper surface of the plate-like part 10 of the ruler and the lower portions of the rollers 1 6 and 1 7 project respectively through spaced rectangular apertures 1 9 and 20 in the part 10.

The roller assembly 1 5 is located on the part 10 by means of an adjustement bar 21 which may be formed from plastics and is formed in its underside with a V-shaped groove 22 which partly embraces the shaft 18, as best seen in Figure 4. To one side of the groove 22 the adjustement bar 21 is supported on a plastics spacer strip 23 so that the rest of the bar extends cantilever fashion across the shaft 18. The adjustement bar 21 and spacer 23 are secured to the part 10 by screws 24 which pass through apertures in the bar and spacer and are in threaded engagement with the part 10. Two further spaced screws 25 pass through the cantilever portion of the adjustment bar 21 and are also in threaded engagement with the ruler 10.

It will be appreciated that by adjusting the screws 25 the cantilever portion of the adjustement bar 21 may be flexed towards or away from the part 10 thus increasing or decreasing the frictional engagement between the bar and the shaft 1 8. In use, the bar is adjusted so that the frictional restraint it imposes on rotation of the roller assembly is such that the ruler may rest on an inclined drawing board without rolling down under its own weight, but yet may be readily overcome by the user in rolling the ruler to a new position. Since the adjustment may simply be effected by merely tightening or loosening the two screws 25, the roller assembly may readily be adjusted to exactly the resistance required, and any wear of the components can be accommodated, or any tendency to jam relieved.

It will be appreciated that the particular details of construction described above are by way of example only. In particular, the parts of the ruler may be made from materials other than the acrylic plastics described. For example they may be formed from any suitable plastics, wood or metal or from a combination of such materials.

The spacer 23 may be of any suitable form, and instead of being a continuous strip might comprise, for example, separate blocks or washers through which the screws 24 pass. Alternatively, instead of the adjustment member 21 being supported cantilever-fashion as described above, the spacer 23 might be omitted, so that the frictional pressure of the bar 21 on the shaft 18 may be adjusted by adjusting any of the screws 24 or 25.

Claims (11)

1. A drawing implement of the kind comprising an operative plate-like element and a roller assembly rotatably mounted on the element in a manner to engage the surface on which the element rests, the roller assembly rotating as the implement is moved over the surface so as to constrain the implement to move linearly, wherein there is mounted on the plate-like element a member which frictionally engages the roller assembly, or a part rotatable therewith, which member is adjustable with respect to the plate-like element in such manner that said frictional engagement may be varied.

2. A drawing implement according to claim 1, wherein the roller assembly comprises two rollers spaced apart on a common shaft, the adjustable member bearing frictionally against a portion of the shaft between the rollers.

3. A drawing implement according to claim 2, wherein the shaft is disposed on the upper side of the plate-like element, the rollers projecting through apertures in the element for engagement with the surface on which the implement rests.

4. A drawing implement according to claim 2 or claim 3, wherein the peripheries of the rollers are ridged or otherwise formed to improve their frictional grip on the surface.

5. A drawing implement according to any of claims 2 to 4, wherein the adjustable member is so mounted on the plate-like element as to extend cantilever-fashion across the portion of the shaft, adjustable means being provided between the member and plate-like element whereby adjustment thereof flexes the member into frictional engagement with the shaft.

6. A drawing implement according to claim 5, wherein said adjustable means comprise screws connecting the adjustable member and the platelike element.

7. A drawing implement according to any of claims 2 to 6, wherein the adjustable member is provided with means to locate the shaft on the plate-like element.

8. A drawing implement according to claim 7, wherein the side of the member facing the platelike element is formed with an elongate groove which partly embraces the shaft.

9. A drawing implement according to claim 8, wherein the elongate groove is V-shaped in crosssection.

10. A drawing implement according to any of the preceding claims, wherein the plate-like element comprises a ruler and/or protractor and is formed from transparent rigid material.

11. A drawing implement substantially as hereinbefore described with reference to the accompanying drawings.