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Multi-tiered-recess screws

Multi-tiered-recess screws description/claims

This application is a continuation-in-part of co-pending application Ser. No. 10/703,115, filed Nov. 6, 2003, entitled “Multi-tiered-recess screws”.

This invention relates to multi-tiered-recess screws, that is to say, screws comprising a driving recess for insertion of a driving tool, which recess comprises a plurality of superimposed recess-tiers of decreasing size. The recess-tiers may be concentric, in which event they are non-circular. Indeed, the invention is particularly concerned with the latter, because these have the additional feature that, whereas the driver has a fixed number of tiers, the screw may have some or all of the recess-tiers, depending on its size and torque driving requirements.

It is a particular feature of this kind of screw that there is a single driver that is suitable for driving a range of sizes of screw. Smaller screws simply have one or two small recesses, while the larger screws have larger recesses also.

GB-A-1150382 appears to be the first disclosure of a screw provided with a multi-tiered recess and a corresponding multi-tiered driver. GB-A-2285940 discloses essentially the same idea. Both these publications describe the advantages provided by the arrangements disclosed. The first is that the recesses are essentially parallel-sided and consequently eliminate cam-out problems that are associated with cross-head recesses. Secondly, they give the possibility of a single driving tool being suitable for driving a wide range of screw sizes.

The single driving tool typically has three (for example) tiers of driving surfaces which are employed to drive large screws having three recess-tiers of recess. However, the same tool can be employed with smaller screws having only two recess-tiers of recess, the largest recess-tier being omitted. Indeed, even smaller screws may have only one, the smallest recess-tier, in their recess and be driven by the smallest tier only of the tool.

GB-A-2329947 discloses a similar arrangement, and WO-A-0177538 discloses recess-tiers that have such a small extent in the recesses of screws and bolts that, at the torques at which the screws are intended to be operated, they cannot be turned unless at least two recess-tiers are both engaged by the tool. Otherwise, the screw is arranged to round out of engagement with the driving tool. This provides a security feature in that only the appropriate tool, having all the requisite driving tiers, will undo the screw.

WO03/025403 discloses a method of manufacture of such screws using cold forming punches. It is possible to make the recesses with some precision, so that the driving tool is a close fit in the recess. This has the very useful feature that recess-tiers can be shallow. Then, screw heads do not need to be large to accommodate the driving tool. Yet, adequate torque can still be applied because a large proportion of the area of each recess is used for torque transmission by virtue of the close tolerance fit. But, equally usefully, the tool fits the screw so closely that, once mated with the driving tool, the screw can be carried solely by the driver when it is offered up to a workpiece. Indeed, with self-tapping wood screws, the connection between driver and screw is so stable that some pressing and simultaneous rotation forces can be applied to the tool, without holding the screw. This can be done without significant risk that the connection will fold as may happen with, for example, Posi-Driv (registered trade mark) screws unless forces are maintained absolutely axial. With the three-tiered screws of the present applicants marketed under the registered trade mark Uni-Screw, the fit is so close that even carrying screws dangling vertically from the driver is possible if carried carefully.

Nevertheless, it would be desirable to improve this feature. This is particularly so with screws having only one or two recess-tiers of recess. It seems that it is partly the plurality of recess-tiers that, at least to some extent, explains why the screw appears to grip the driver so effectively. So, with smaller screws having just one recess-tier of recess the feature is not so evident. It is an object of the present invention to improve that feature.

In accordance with this invention there is provided a screw and driver system comprising a range of screws and a driver for said range, each screw comprising a head having a driving recess in its surface for engagement by said driver and a longitudinal axis, in which the recess of larger screws in the range have a plurality of superimposed recess-tiers of decreasing size with increasing depth from said surface, each recess-tier having substantially parallel driving surfaces substantially parallel said longitudinal axis, and in which said driver and recess are shaped so that, when the driver is engaged with the recess of any screw in said range, torque applied to the driver is transmitted to the screw through said driving surfaces; wherein, an interference is provided between the driver and the recess causing deformation of the recess when the driver is inserted therein.

Preferably, said interference comprises at least one recess-tier of at least smaller screws in said range having a rib parallel said longitudinal axis and encroaching into the space of said recess-tier occupied by said driver when it is engaged with said recess, whereby engagement of the driver with the recess causes deformation of said rib and hence creation of an interference fit of said driver in said recess.

Preferably all the screws in the range have said rib. The rib may be in a recess-tier which is common to all screws in the range. Alternatively, the rib may be in the single recess-tier of single recess-tier screws, and a different recess-tier in screws having a plurality of recess-tiers.

The invention also provides a screw that fits in said range of screws in said system, which screw includes a recess-tier having said rib.

Preferably, said recess-tiers of said larger screws are non-circular polygons in section. The polygons may be concentric. They may be the same polygons. They may be angularly offset with respect to one another. The smaller screws in said range may have only one recess-tier in their recess.

Screws in accordance with the present invention are conveniently made by a cold forming process in which the recess is formed by a punch of corresponding shape to the recess being formed. In this event, preferably, said recess rib is formed by a groove formed in the flank of said punch.

Preferably, said rib is the full depth of only one recess-tier, where there are multiple recess-tiers.

One advantage of the present invention is that the rib can be large enough to ensure an interference fit with the driver but, when it is only in one recess-tier, it does not increase substantially the overall force required to engage the driver with the recess, particularly not on larger screws.

Preferably, it is the smallest recess-tier in each screw of the range that is provided with said rib. Indeed, it is on larger screws that the dimensions of the smallest recess-tier are most susceptible to fluctuation in dimensional tolerance.

Where the recess-tiers of the recess are polygonal in section having several flanks, the rib may be central in one flank. Alternatively, and this is preferred, the rib may be in a corner between two flanks. This has the advantage that a sharp corner of the driving tool bites into the rib more easily than the rib simply being flattened by the flank of the tool. Indeed, a smaller rib is preferably provided in each corner between the flanks of the recess-tier. This maintains the central location of the driving tool in the recess.

• Provisional Patent
• Utility Patent

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