GB2129348A - Screws - Google Patents

Abstract

An angle-drive screw formed by moulding or casting has a head provided with upstanding segments 6 defining therebetween the screwdriver recess 4. The upper surfaces of the segments are tapered downwardly towards the circumference of the screw head. The bottom of the screwdriver recess extends upwardly from the axial centre to the circumference of the screw. A substantial improvement in performance can be achieved by a single compressing operation, in which the compression force is applied to the upstanding segments 6 in a substantially axial direction so as simultaneously to provide all the walls of the screwdriver recess with an undercut configuration, Fig. 5. <IMAGE>

Description

SPECIFICATION Screws This invention relates to screws.

One known form of screw is designed so that it can be operated by a screwdriver which is tilted with respect to the axis of the screw. Screws which have this capability will be referred to herein as "angle-drive" screws. The known screw is of the cross-head type, and the cross-shaped recess for the screwdriver is so shaped that a large driving force can be transmitted from the end of the screwdriver to the screw even when the end enters the recess at a relatively large angle, for example 200, to the axis of the screw.

Angle-drive screws have substantial advantages in that they can be used in places in which ordinary screws would be virtually inaccessible. For example, if there is an internal corner where two walls meet, it can be very difficult, or impossible, to drive a screw into one of the walls very close to the corner because the other wall would interfere with the rotation of the screwdriver. This can be avoided if the screwdriver can be tilted away from the wall during the screwing operation.

However, when using an angle-drive screw, as the driving force increases for a given tilt angle (i.e. the angle between the axes of the screw and the screwdriver), or alternatively as the tilt angle increases for a given driving force, an action known as "camming out" occurs, whereby the end of the screwdriver is lifted out of the screwdriver recess by virtue of a camming action between the tip of the screwdriver and the side-walls of the screwdriver recess. This can damage the screw, and also limits its usefulness. The permissible tilt angle and driving force can be made relatively large by using a hard metal for the screw and by using a rather expensive manufacturing technique to form the screwdriver recess in such a way that the side-walls are undercut. However, both these methods substantially increase the cost of the screw.

The present invention relates to an angle-drive screw, desirable of the cross-head type, in which the screwdriver recess has side-walls which have been provided with an undercut configuration by compressing the head of the screw in a substantially axial direction.

It has been found that the desired undercutconfiguration of the side-walls can be achieved without requiring radially inwardly directed forces to be applied to the head of the screw.

Accordingly, because only an axially-directed force is required, screws which have the desired configuration for permitting large driving forces and tilt angles to be used can be manufactured simply and inexpensively. In the preferred embodiment, only a single squeezing operation or impact is used to provide all the side-walls simultaneously with the undercut configuration.

Preferably, the screw is initially formed by a casting or moulding operation. The side-walls of the recess would initially lie in planes substantially parallel to the axis of the screw, or perhaps be slightly tapered outwardly to facilitate the moulding operation. Thereafter the undercut configuration, which cannot be achieved using a simple moulding operation, can be provided easily in the manner described above.

In its initial form, the head of the screw preferably has upstanding segments which are compressed by the axially-directed force to produce overhangs which give the desired undercut configuration to the side-walls.

Preferably, each upstanding segment has its upper surface tapering downwardly toward the circumference of the screw head. This, it is believed, facilitates the inward deformation of the segment, and hence the creation of the overhang, when the head of the screw is subjected to the axial compression force.

An arrangement embodying the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view of an angle-drive screw in its initial state after moulding, Figure 2 is a section along the lines A-A of Figure 1, Figure 3 is a section along the lines B-B of Figure 1, Figure 4 is a plan view of the screw of Figure 1 after it has been subjected to an axial compression force, Figure 5 is a section along the line AA-AA of Figure 4, and Figure 6 is a section along the line BB-BB of Figure 4.

Figures 1 to 3 show the head 2 of an angledrive screw. The screw has been formed by casting, using a metal which is preferably fairly malleable and inexpensive, such as a zinc alloy. A material known under the trade name Mazak has been found suitable.

The screw head 2 has a cross-shaped screwdriver recess 4 to enable the screw to be driven using a cross-head screwdriver such as those sold under the trade names Phillips and Pozidriv.

The top of the screw head 2 is formed with four segments 6, which define between them the screwdriver recess 4. The upper surface of each segment 6 is curved, and extends gradually upwardly from the outer circumference of the screw head 2. Each segment 6 also has two substantially vertical faces 8, which form the sidewalls of the recess 4 and are the faces which receive the driving force applied by the screwdriver.

The recess 4 for the screwdriver is relatively wide and deep, and permits the tip of a screwdriver to be inserted at a fairly large angle relative to the axis of the screw.

It should be noted that the screw of Figures 1 to 3 operates quite adequately as an angle-drive screw. It permits fairly substantial driving forces to be applied to the screw at a tilt angle of up to about 200. Beyond that angle, the screwdriver tends to "cam out".

To improve the performance of the screw, the head 2 is subjected to a downward, axiallydirected blow, which has the effect of compressing the segments 6.

The configuration of the head of the screw after it has been subjected to this treatment is shown in Figures 4 to 6.

Referring to Figures 5 and 6, it will be noted that the segments 6 are no longer, or only slightly, upstanding. Further, the side-walls 8 now have an undercut configuration, i.e. opposed side-walls 8 lie in planes which converge in the upward direction.

Although the side-walls 8 are shown as being pianar, the compression force applied to the segments 6 may alternatively cause them to have a concave configuration.

It will be further noted, when comparing Figures 1 and 4, that, at the mouth of the screwdriver recess 4, adjacent walls 8 initially extend at obtuse angles relative to each other, but, after the compression force is applied, extend substantially at right angles to each other, the mouth of the recess 4 thereby becoming slightly narrower.

The overall effect of the compression force applied to the segments 6 is to permit the screw to be driven at a greater tilt angle, for example 300 instead of 200, or alternatively to allow greater driving forces to be applied at the same, relatively low tilt angle.

This is achieved mainly because of the configuration of the side-walls 8, which, because of their inclination, tend to force the end of the screwdriver downwardly when the latter drivingly engages the side-walls thereby to counteract the camming out effect.

The axial compression force can be applied in a variety of different ways. The head of the screw can be impacted with a flat surface extending perpendicular to the axis of the screw. The use of segments 6 which are upstanding with respect to the outer circumference of the screw particularly facilitates the use of a flat impacting surface, and the use of segments which have their upper surfaces inclined downwardly toward the outer circumference facilitates the inward deformation of the segments 6 when impacted with a flat surface.

It may be found desirable to have a mandrel inserted into the central part of the screwdriver recess 4 when the segments 6 are compressed; in these circumstances, the compression could be effected by a movable collar surrounding the mandrel.

As mentioned above, the screw is also usable as an angle-drive screw prior to the compression force being applied to produce the undercut configuration. The invention also extends, in another aspect, to an angle-drive screw in that form; the screw is preferably, but not essentially, so designed that its head can subsequently be compressed to achieve the undercut configuration. Preferably, the head of the screw has segments which are upstanding at least adjacent the centre of the screw head so as to provide a relatively deep recess, while the outer circumference of the screw head, at least at the positions between adjacent segments, is at a relatively low height so as not to restrict the tilt angle.

Claims (17)

1. An angle-drive screw having a screwdriver recess with side-walls which have been provided with an undercut configuration by compressing the head of the screw in a substantially axial direction.

2. A method of making an angle-drive screw, comprising forming a screw blank having a head provided with upstanding segments defining therebetween a screwdriver recess, and applying to the upstanding segments a compression force to provide the side-walls of the screwdriver recess with an undercut configuration.

3. A method as claimed in claim 2, wherein the screw is of the cross-head type.

4. A method as claimed in claim 2 or claim 3, wherein the screw blank is formed by casting or moulding.

5. A method as claimed in any one of claims 2 to 4, wherein the screw blank is so formed that the sidewalls of the screwdriver recess lie in a plane substantially parallel to the axis of the screw or slightly tapered outwardly with respect to said axis.

6. A method as claimed in any one of claims 2 to 5, wherein the upper surface of each upstanding segment of the screw blank tapers downwardly towards the circumference of the screw.

7. A method as claimed in claim 6, wherein said upper surfaces are curved.

8. A method as claimed in any one of claims 2 to 7, wherein the bottom of the screwdriver recess extends upwardly from the axial centre of the screw to the circumference thereof.

9. An angle-drive screw having a head provided with a base portion and upstanding segments defining therebetween a screwdriver recess the bottom of which extends upwardly from the axial centre of the screw to the circumference thereof.

10. A screw as claimed in claim 9, wherein the screwdriver recess is open-ended.

1 A screw as claimed in claim 9 or claim 10, wherein the upper surfaces of the segments taper downwardly towards the circumference of the screw head.

12. A screw as claimed in claim 1 wherein said upper surfaces are curved.

13. A screw as claimed in any one of claims 9 to 1 2, wherein the width of the screwdriver recess continuously decreases towards the circumference of the screw head.

14. A screw as claimed in any one of claims 9 to 13, wherein the opposed side-walls of the screwdriver recess are substantially parallel to the axis of the screw or slightly tapered outwardly with respect thereto.

1 5. A screw as claimed in any one of claims 9 to 14, which is of the cross-head type.

16. A screw as claimed in any one of claims 9 to 15, which has been formed by casting or moulding.

17. An angle-drive screw substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings.

1 8. An angle-drive screw substantially as herein described with reference to Figures 4 to 6 of the accompanying drawings.