Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Thread or shank structure
Reexamination Certificate
2000-03-21
2001-12-04
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Thread or shank structure
C411S399000, C411S387600
Reexamination Certificate
active
06325583
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
2. Description of the Related Art
The invention relates to a screw with a shank provided at least partly with a thread, a boring and/or penetrating point and a head equipped with a tool drive for fastening wooden laths to a roof or wall substructure comprising wood among other alternatives.
Heretofore laths, especially roof laths, have normally been fastened by nails, even though tensile loading of nails in shank direction should be zero or only slight. Predrilled holes are necessary to ensure that the nailing process does not cause splitting, especially in the case of larger nails.
Precisely in the fastening of laths on which the actual roof covering or wall siding will ultimately be fastened, it is the roof or wall structure that is usually the weak point, because tensile forces developed during suction effect cannot be transmitted.
The use of screws has never been considered, because of the risk of splitting of the relatively narrow laths by the screw head as the screws are being tightened.
The object of the invention is to provide a screw of the type cited in the introduction, which screw is particularly suitable for use in fastening wooden laths to a roof or wall substructure.
BRIEF SUMMARY OF THE INVENTION
According to the invention, this is achieved in that one threaded portion each adjoining at least the boring and/or penetrating point and the head is provided on the shank of the screw, and these two threaded portions have the same major diameter but different thread pitches, and in that the outside diameter of the head is as large as or slightly larger than the major diameter of the threaded portions.
By the use of such a screw to fasten wooden laths, these can be loaded both in compression (as in the case of heavy snow loads) and in tension (as in the case of suction effect). In this way a durable composite structure is ensured both in compression and in tension. Such fastening does not involve maintaining a lath at a specified spacing from a substructure, since such laths practically always rest on similar wooden material, such as cross lathwork with panelling on rafters, or else are screwed together with the wooden beams or the like disposed thereunder, possibly with a vapor seal disposed therebetween.
Precisely in the case of such laths it is advantageous for lath and substructure to press strongly against one another, because the thread is engaged both in the substructure and in the region of the lath. Minor dimensional variations caused by humidity in the region of the lath and also in the region of the substructure can be accommodated when the lath is pressing against the substructure.
Since the outside diameter of the head is as large as or only slightly larger than the major diameter of the threaded portions, only a very small head is countersunk into the lath material, thus also preventing the splitting effect. Nevertheless, the screwed lath can be safely loaded in tension, since a threaded portion acting as a bracing thread is present underneath the screw head.
To reduce the driving torque, there can be provided a thread-free shank portion disposed between the threaded portions associated with the end regions of the shank.
An advantageous embodiment is achieved when the thread-free shank portion corresponds at least approximately to the minor diameter of the two threaded portions. Thereby the driving torque is relatively small even for long screws, since a corresponding portion of the screw can be drawn in, without particularly large frictional forces, by the threaded portion formed at the free end, whereupon the threaded portion adjacent to the tool drive can engage in the thread that already exists in the lath.
For manufacturing reasons alone it is advantageous for the two threaded portions to have at least approximately the same length. Relatively short threaded portions, which can be readily made precisely in the case of particularly long screws, are sufficient for transmission of the tensile and compressive forces.
It is further proposed that the ratio of minor diameter to major diameter of the two threaded portions be approximately 1:1.5 to 1:2, preferably 1:1.7. By virtue of this relatively deep thread, it is ensured that relatively large forces can be transmitted, because the thread flanks protrude well above the minor diameter and thus can penetrate deep into the adjoining material of the lath.
It is also expedient for the minor diameter in the region of the one threaded portion close to the head to merge into the outside diameter of the head via conical expansions. Thereby it is ensured that splitting of the laths is not initiated even during countersinking of the head. By virtue of this special transition region, the splitting risk is precluded despite the need to provide a head in which the tool drive is located.
For particularly long screws, it is advantageous for the length of the threaded portions to be constant despite different total length of the screw, and for the length of the shank portion which may be thread-free to be varied. The special length of the threaded portions adjacent to the two ends of the screw is completely sufficient for transmission of compressive and tensile forces, and so it does not have to be increased even in very long screws. Thereby the manufacture of screws having different lengths is also simplified, since the threaded portions always have the same length regardless of the screw length.
To provide even more effectively for special load cases, especially with regard to roof pitch and to roof laths laid across the roof slope, or to particular forces to be expected, it is expedient for the screws to be driven in at an acute angle to a central longitudinal plane of the laths to be fastened. In a special type of lath fastening, it is also possible for the screws driven in successively in the long direction of a lath to be inserted at an acute angle in opposing directions relative to a central longitudinal plane of the lath. Thereby there is achieved particularly effective anchoring of the lath on the substructure and, as a further benefit, the danger of tilting of the lath under large loads is also precluded.
A further option provides that the shank portion disposed between the two threaded portions associated with the end regions of the shank is equipped with a thread identical or similar to the two threaded portions or with a thread of reduced diameter. Thereby additional bracing is possible even in the region between the two threaded portions.
Another embodiment provides that the shank portion has a thread of reduced major diameter compared with the major diameter in the threaded portions, while the minor diameter is substantially equal over the length of the threaded portions and of the shank portion. In this way, therefore, a substantial reduction of the driving torque can also be achieved, since the screw does not make full surface contact over its entire length in the thread cut by the screw itself. Nevertheless, the necessary tensile and compressive forces can be transmitted.
A further advantage is achieved in that the flank angle of the threaded portions and if applicable of a thread formed on the shank portion is approximately 40° and the thread pitch is at least approximately 3 mm. The driving-in process can therefore be completed quite quickly by virtue of the large thread pitch. Because of the relatively sharply tapered thread, a cutting action takes place in the region of the roof lath, thus further reducing the risk of splitting.
A particularly advantageous embodiment provides that the diameter of the thread-free shank portion is reduced from the starting wire material to the minor diameter of the threaded portions. Especially by such reduction of the shank portion, it can be ensured that the diameter of the shank portion ultimately corresponds to the minor diameter of the threaded portions, and so full advantage can be taken of the possibilities of reducing the torque for driving in the screw.
In this connection there can also be conceived anothe
Mattle Paul
Thurnherr Ernst
SFS Industrie Holding AG
Volpe and Koenig P.C.
Wilson Neill
LandOfFree
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