GB2259939A

GB2259939A - Anti-tamper bolt

Info

Publication number: GB2259939A
Application number: GB9119106A
Authority: GB
Inventors: Brian Valentine Crankshaw
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-09-07
Filing date: 1991-09-07
Publication date: 1993-03-31
Also published as: GB9119106D0

Abstract

The present invention provides an anti-tamper bolt (11) which requires the use of two hands in order to draw it. A rotatable element (15) is mounted around the shank (14) of the bolt (1) enabling the bolt (1) to be drawn only when a raised portion (30) mounted on the element (15) of the bolt is positioned within a sympathetic groove or key-way (26) formed on the end of the bolt. Similarly the raised portion (30) may be formed on the bolt and a key-way cut in the element (15). More than one raised portion (30) and sympathetic key-ways may be formed on the shank and/or within the element (15) so as to enhance the device. <IMAGE>

Description

AN ANTI-TAMPER CLOSURE MECHANISM This invention relates to an anti-tamper closure mechanism, and more specifically, but not exclusively, it relates to an anti-tamper bolt or latch.

Bolts have existed for many years. The problem with bolts has been that intruders have been able to smash small panels of glass surround close to where a bolt is positioned and by manipulation of a head of the bolt, for example by using a piece of wire, an intruder has been able to draw a bolt relatively easily.

The problem of drawing such bolts has to some extent been made more difficult by tamper proof bolts which have comprised threaded portions arranged to lock a bolt into a closed position. However, these tamper proof bolts, although presenting some obstacle to an intruder, have still been relatively easy to undo, especially if an intruder has the requisite tool or key for removing the locking mechanism. Once the locking mechanism has been removed the intruder again simply draws the bolt and unauthorised entry may then take place.

It is an aim of the present invention to provide an anti-tamper bolt which may not be drawn easily. Thus presenting a bolt which will act as a more reliable deterrent to an intruder.

According to one aspect of the present invention there is provided an anti-tamper bolt having a locking means rotatably moveable with respect to a shaft of a bolt such that when the locking means is moved to a predetermined position the bolt may be drawn.

According to a second aspect of the present invention an anti- tamper bolt is arranged to move in an axial direction and has means to prevent the bolt being drawn, characterised in that the means is movable about an axis of the bolt.

The means may comprise a rotatable capstan or thimble which has a key-way cut in it so that when the key-way is aligned with a raised portion running along the surface of the shaft of the bolt, the bolt may be drawn such that the raised portion passes through the key-way. A plurality of raised portions and sympathetic key-ways or grooves may be provided on the shaft and within the thimble respectively.

Preferably however, the bolt has at least one key-way or groove cut along its shaft or body and a capstan or thimble has at least one key or raised portion mounted within its envelope such that when the or each key-way is/are aligned with the or each key or raised portion(s) extending along at least a portion of an inner surface of the capstan or thimble, the bolt may be drawn. On drawing the bolt the key passes through the key-way. A plurality of keys or raised portions and key-ways or sympathetic grooves may be provided. This leads to a more complex device.

Advantageously one raised portion and one sympathetic groove is provided on the shaft and a second raised portion and sympathetic groove is provided within the thimble such that the thimble may only be aligned relative to the shaft in one orientation, thus making it less likely that the thimble will fall into position to enable the bolt to be drawn. The respective grooves may be of different widths and/or depths so as to accomodate only the related raised portion.

A resilient means may be placed within a suitably formed orifice or slot in the body of the bolt, substantially perpendicular to the axis of the bolt, so as to urge against an inner wall of a bolt housing or frame, thereby maintaining the bolt in a particular position. A steel ball may be placed between the resilient means, which is preferably a small spring, and the wall of the bolt housing guiding the bolt.

A hole may also be provided in the wall of the housing supporting the bolt and this may serve to locate the spring and the steel ball, thereby holding the bolt in a particular position.

The bolt, the housing supporting the bolt and the thimble, may all be formed from mild steel or brass or a similar machinable material.

An embodiment of the invention will now be described, by way of an example only, and with reference to the following figures in which: Figure 1 shows a plan view, in part section, of a bolt mounted in a housing and supported on a bracket; Figure 2 shows a plan view of a shaft of the bolt of Figure 1; Figure 3 illustrates a side elevational view, in part section, of a thimble; Figure 4 shows details of a spring and ball-bearing fitting into a suitable recess in the shaft of the bolt; and Figure 5 shows a section along the line A-A of Figure 2.

Referring to the figures a bracket and frame 10 for receiving a bolt 11 is of a standard extruded form designed to guide the round section of the bolt 11. A small hole 12 is drilled through one side of the shaft of the bolt 11. The hole 12 receives a spring 12A on which is mounted a small steel ball 13. The shank 14 of the bolt 11 has two diameters indicated by diameter D1 and diameter D2.

The smaller diameter D2 has two narrow slots or key-ways 16 machined along a portion of its length. The larger diameter Dl, contains the normal threaded portion which receives a knurled knob 15 with which the bolt 11 is operated, as described below.

Milled slots or cut-outs 26A and 26B machined as a standard at a rear end of the frame 10 result in the formation of a short bridge section 17. The bore of the section 17 is fitted with the knurled knob or thimble 15 which has diameters D3 and D4 and a bore. The larger of these diameters D4 is either knurled or fluted to afford finger grip. The smaller diameter extends through the bridge by an amount which allows it to be either swaged or fitted with a split ring or circlip (not shown) in order that the knob or thimble 15 is captive but remains free to revolve.

The bore of the knob or thimble 15 is broached to produce an integral key 30 which extends back from the inner face. The design of the unit is such that on attempting to draw the bolt 11 back from the forwards secured position, the tail of the bolt being of a diameter which will allow it to pass through the thimble or knob 15, is prevented from doing so by the integrally cut key 30 within the thimble bore. Only when the key-ways in the bolt and the key in the bore are in alignment with one another will the bolt draw back to the open position and a door (not shown), onto which the bolt is fitted, be openable.

To secure the bolt in the lock position the bolt is drawn forward along the first key-way in which it is already engaged and it is prevented from moving any further until the thimble is turned to locate the second key-way at which the bolt will continue to its locked position. The thimble is then turned by random degree to ensure misalignment of key to key-way.

The function of the spring loaded steel ball 13, referred to previously, is to prevent the bolt 11 from being set back against the thimble bore in order to locate the key-way using one hand. Generally the bolt will be seen to settle to a point slightly forward of the thimble bore as the bolt locates the drilled hole 12 in the housing. The aforementioned bolt in frame therefore will prevent an intruder from breaking a small portion of a glass panel and levering a bolt open by using only one hand. By virtue of the key and key-way and the sprung ball arrangement it is virtually impossible to draw the bolt 11 by using only one hand. The safety feature therefore ensures that bolts may easily be drawn from the inside by using two hands but are difficult to draw from the outside by an intruder.

The application of the bolt does not only lend itself to use as a security device for doors and windows but also it could be used as a child-proof lock on domestic medicine cabinets. It could also be used for example on cupboards containing chemicals or other hazardous substances or as a childproof lock.

It will be appreciated that variation to the above embodiment may be made without departing from the scope of the invention.

Claims

1. An anti-tamper bolt having a locking means rotatable with respect to a shank of a bolt such that when the locking means is moved to a predetermined position the bolt may be drawn.

2. An anti-tamper bolt being arranged to move in an axial direction and having means to prevent the bolt being drawn, characterised in that the means is rotatable about an axis of the bolt.

3. An anti-tamper bolt according to claim 1 or 2 wherein the rotatable means comprises a capstan encompassing a shank of the bolt, a key-way being defined on an inner surface of the capstan, which key-way when aligned with a raised portion disposed on the surface of the shank of the bolt, permits the bolt to be drawn such that the raised portion passes through the key-way.

4. An anti-tamper bolt according to claim 1 or claim 2 wherein a key-way is defined on a surface of the shank of the bolt and a capstan surrounds the shank of the bolt, a raised portion being defined on its inner surface such that when the raised portion is aligned with the key-way the bolt may be drawn.

5. An anti-tamper bolt according to claim 3 wherein a plurality of key-ways and sympathetic raised portions are provided such that the capstan may be aligned relative to the shaft in only one orientation.

6. An anti-tamper bolt according to any preceding claim wherein the or each key-ways and the or each sympathetic raised portions is/are linear.

7. An anti-tamper bolt according to claims 5 or 6 wherein respective key-ways are of different widths and/or depths so as to accommodate respective raised portions.

8. An anti-tamper bolt according to any preceding claim wherein resilient means is positioned within a suitably formed recess in the body of the bolt so as to urge the shank of the bolt against an inner wall of a bolt housing supporting the shank.

9. An anti-tamper bolt according to claim 8 wherein the resilient means comprises a spring on which urges a steel ball against an inner surface of the bolt housing.

10. An anti-tamper bolt substantially as herein described with reference to the Figures.