GB2106839A - Drawing instrument - Google Patents

Abstract

A pair of compasses/dividers is provided with a finger-piece in the form of a hollow cap 36 engageable in a bow top body 16 by a bayonet joint. The cap 36 provides a storage compartment for storing spare point and/or pencil lead elements to replace the lead element 22 at the end of one of the legs 12. <IMAGE>

Description

SPECIFICATION Drawing instrument This invention relates to a drawing instrument, such as a drawing compass or dividers, of the kind comprising a pair of legs which terminate at their lower ends in an element, for example in a point element or a pencil lead element, at least one of these elements being detachably fitted in place (hereinafter referred to as a drawing instrument "of the kind specified"). Each leg may be pivoted at an upper end to a bow top having an upwardlyprojecting finger-piece by which the instrument can be rotated when gripped, in use, between a finger and thumb of the user.

In known constructions of drawing instruments of the above kind, the finger-piece has generally been formed as an integral part of the bow top which is commonly produced as a one-piece moulding or casting. In such known arrangements,thefingerpiece has moreover usually been solid or has been formed with an interior recess adapted to receive an upwardly-projecting extension of a separate centralising member which moves angularly when either leg is opened out or closed up, thereby to maintain the finger-piece and bow top centralised with respecs to the legs, as described for example in our prior British Patent Specifications Nos. 1533348 and 1533349.

According to the present invention there is provided a drawing instrument of the kind specified comprising a storage compartment adapted to store one or more replacement elements, for example a point element or pencil lead element, so that said replacement element or elements can be carried around on the instrument and so that said at least one element detachably fitted in place is capable of being detached from the respective leg and replaced by a, or the, replacement element from the storage compartment.

The drawing instrument may have a finger-piece comprising or including a separately formed cap, said finger piece being on a bow top and adapted to hold the replacement element or elements captive within an interior cavity constituting the storage compartment. The cap is, preferably, detachable so that the replacement element or elements for the instrument is/are only accessible and removable from the storage compartment when the cap is detached.

Thus, a spare pencil lead element may conveniently be carried with the instrument for replacement of an existing pencil lead element detachably fitted to the lower end of one of the legs when constituting a compass, or for substituting in place of an existing point element, detachably fitted to the lower end of one of the legs, for converting the instrument from a pair of dividers into a drawing compass. Or, an extra point element may be carried to permit the instrument, in the form of a drawing compass, to be converted into a pair of dividers.

In preferred embodiments, the interior cavity which accommodates such captive pencil lead or point element or elements is defined at least partly and, preferably, substantially entirely by a hollow interior space within the cap, and the cap is, preferably, formed of a transparent plastics material whereby the contents are readily visible. The body part of the bow top may also be formed of plastics material but this will generally be opaque and different from that of the cap.

Preferably the cap is detachably fitted to the body of the bow top by means of an interlocking joint means, for example a bayonet type joint, to safeguard against accidental removal and by use of plastics materials, possibly providing a significant degree of resiliency, an additional high frictional resistance to the joint becoming loose can be attained so that the cap remains firmly fitted and its function as a finger-piece for rotating the instrument remains unimpaired. Conveniently, the cap is in the form of a cylinder, closed at its outer end, of which the open inner end plugs into and interlocks within a socket in the top of the body of the bow top.

Also in preferred embodiments, the legs of the drawing instrument are mechanically interconnected at their upper ends by gears, such as sector gear teeth, accommodated within the body of the bow top between fork arms thereof in order to maintain the bow top centralised when one or other of the legs is moved angularly outwards or inwards.

Such gearform of centralising means avoids the need to extend into the upper part of the bow top and finger-piece and thereby facilitates the design of the finger-piece in the form of a cap usable as a receptacle for a pencil lead of point element or elements.

By way of example, a drawing instrument representing one preferred embodiment of the invention is illustrated in the accompanying drawings and will be more particularly described with reference thereto.

In the drawings, Figure lisa front elevational view of the intrument showing a pair of legs pivoted to a bow top fitted with a detachable cap component; Figure 2 is side elevational view of the upper portion of the instrument; Figure 3 is a view, on a larger scale, of the upper end portion of the two legs; Figure 4 is a sectional view on line IV-IV of Figure 2 showing the bow top with the legs removed; and Figure 5 is a sectional view on line V-V of Figure 4; and Figure 6 is a top plan view of the bow top with the cap component removed.

The instrument as illustrated in the drawings is in the form of a drawing compass having a pair of legs, 10 and 12, pivoted at their upper ends upon pivot pins or studs 15 between fork limbs 14, 14,oft of a bow top body 16 and mechanically interconnected by meshing sector gear teeth 18, 18, (Figure 3).

At its lower end, the leg 10 is fitted with a fixed point element 20 and the leg 12 is fitted with a removable pencil lead element 22. To accommodate and detachably hold the pencil lead element 22, the lower end of the leg 12 is slotted to provide a narrow longitudinal channel 24 opening out along the exterior side face of the leg and shaped to provide a lead-receiving socket 26 extending lengthwise of the channel adjacent its base. Outwardly of the socket 24 a headed cross-pin 28 extends through the wide walls of the channel 24 and a screw-threaded projecting end portion thereof is fitted with a milled clamping nut 30 whereby the walls of the channel 24 can be contracted together to apply clamping pressure to hold the lead element 22 in place.Slackening off the clamping nut 30, however, enables the lead element 22 to be removed for replacement by a new lead element, or alternatively by a point element of appropriate dimensions whereby the instrument can be converted into a pair of dividers.

The legs 10 and 12 are advantageously composed of moulded glass fibre reinforced plastics material and opposite faces are both recessed (as indicated at 32) to provide an I-shaped cross-sectional configuration over a major part of their length for lightness and strength. In using plastics mterial for the legs of such instruments it must be appreciated that it is essential to avoid any undue flexibility or lack of rigidity which would impair the precision of the instrument.

The bowtop body 16 is also moulded of plastics material, conveniently nylon, and its upper part which bridges across the depending fork limbs 14, 14, has a socket 34 formed in the top thereof which receives the open lower end of an upstanding, removable, hollow cylindrical cap 36 closed at its upper end.

The cap 36 is formed of transparent plastics material and, as well as constituting a finger-piece which can be gripped between a finger and thumb of the user for rotating the instrument, it also constitutes a receptacle for containing within its hollow interior 37 a pair of spare pencil lead elements 22' together with an additional point element 20' which can be substituted for the element 20 when it is required to use the instrument as a pair of dividers.

A bayonet type joint detachably secures the cap 36 in the socket 34 in interlocking relationship. This is achieved by a pair of short circumferentially extending radial lugs 40,40, integrally moulded around the base of the cap 36 which engage beneath counterpart portions 42,42, in the walls of the socket 34 when the cap is turned after insertion. The walls of the socket 34 are also apertured towards the bottom to facilitate moulding a shape which accommodates the radial lugs 40,40, of the cap which provides radial projections 44, 44, forming abutments stops effective to limit the extent of rotation of the cap within the socket. The dimensions and tolerances are also such that the cap 36 is engaged within the socket 34 under a significant frictional force so that it is firmly held in poisition and will not readily become inadvertently detached.

This form of construction described is well adapted for economical mass production methods or manufacture and is readily assembled, as well as providing benefits to the user.

In an alternative embodiment only an end portion of the fingerpiece may comprise the cap and the cap may screw into or onto the remainder of the finger piece. The cap need not then be hollow and could comprise a screw-in plug. The remainder of the fingerpiece may or may not be integrally formed with the bow top.

Claims (16)

1. A drawing instrument of the kind specified comprising a storage compartment adapted to store one or more replacement elements, for example a point element or pencil lead element, so that said replacement element or elements can be carried around on the instrument and so that said at least one element detachably fitted in place is capable of being detached from the respective leg and replaced by a, or the, replacement element from the storage compartment.

2. An instrument as claimed in Claim 1 comprising a finger-piece in the form of, or having, a separately formed cap, said finger-piece being on a bow top of the instrument and adapted to hold captive within an interior cavity constituting said storage compartment said replacement element or elements.

3. An instrument as claimed in Claim 2 in which the cap is detachable from the remainder of the instrument.

4. An instrument as claimed in Claim 2 or Claim 3 in which the cap is hollow and the interior cavity is at least partly defined by the cap.

5. An instrument as claimed in Claim 4 in which the interior cavity is defined substantially entirely by the cap.

6. An instrument as claimed in any one of Claims 2 to 5 in which the cap is of transparent plastics material.

7. An instrument as claimed in any one of Claims 3 to 6 in which the finger-piece comprises the cap and the cap is detachably fitted to the bow top by interlocking joint means, for example, a bayonet joint.

8. An instrument as claimed in Claim 7 in which said interlocking joint means provides frictional resistance to the joint becoming loose on relative rotation of the cap with respect to the remainder of the instrument in at least one direction of rotation of said cap about it axis.

9. An instrument as claimed in Claim 8 in which the cap is generally tubular cylindrical, closed at its outer end, the end opposite said closed and being for plugging into and interlockable within a socket in the bow top.

10. An instrument as claimed in Claim 9 in which said interlocking joint means is a bayonet joint, the cap is a one piece moulding and provided with integral radially outwardly extending lugs engageable underneath counterpart portions on the walls of the socket after insertion of the cap in the socket.

11. An instrument as claimed in Claim 10 in which abutment stop means is provided to limit the extent of rotation of the cap within the socket.

12. An instrument as claimed in any claim dependentfrom Claim 2 in which the legs are mechanically interconnected by gears, for example sector gear teeth, accommodated within the bow top between fork arms thereof.

13. An instrument as claimed in any claim de pendentfrom Claim 2 in which the bow top is of plastics.

14. An instrument as claimed in Claim 1 comprising a finger-piece and bow top substantially as herein described with reference to Figures 1,2 and Figures 4 to 6 of the accompanying drawings.

15. An instrument as claimed in Claim 1 comprising mechanically interconnected legs substantially as herein described with reference to Figure 3 of the accompanying drawings.

16. A drawing instrument of the kind specified substantially as herein described with reference to the accompanying drawings.