Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Pilot end having means enhancing fastening or installation
Reexamination Certificate
2000-03-28
2001-12-11
Saether, Flemming (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Pilot end having means enhancing fastening or installation
C411S387100, C411S311000, C411S413000
Reexamination Certificate
active
06328516
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a screw comprising a shank portion, a thread, a conical tip, and at least one cutting edge to facilitate penetration of the screw into a workpiece upon being turned.
BACKGROUND OF THE INVENTION
In a known screw of this kind (JP 5-196 021 A)cutting fins as well as threads are provided in common in the tip area up to the free end of the screw.
In another known screw the cutting edge is formed at a so-called cutting channel, i.e. a notch which continues across the tip area and into the shank of the screw (DE 295 13 571 U1).
Further known is a screw which comprises an abrasive edge zone embodied by a plurality of fins in the region of the screw tip where there is no thread, the fins being oriented in the direction of the longitudinal axis of the screw (DE 195 25 732 A1).
Normal wood screws, especially when being turned to enter into softwood, such as coniferous wood, produce a splitting effect. That is true particularly of screws which have a great diameter. The screws penetrating the wood compact the wood fibers transversely of the direction of the fibers at two diametrically opposed locations of the screw so that frequently the wood suffers cleavage. Thus the cohesion of the wood is deteriorated and, therefore, the retaining force of the screw is diminished.
SUMMARY OF THE INVENTION
It is an object of the instant invention to provide a screw as described above which is capable to reduce the cleaving effect of the screw when screwed into a workpiece, especially a wooden workpiece.
It is a further object to provide a screw which provides an increased retaining force when screwed into a workpiece, especially a wooden workpiece.
The present invention serves to meet these and other objects.
Preferred embodiments of the invention are recited in the subclaims.
With the invention, the cutting edges provided in the tip area at the fins projecting beyond the core diameter penetrate into the wood at locations equally distributed around the periphery of the screw tip of the compacted fibers, cutting into the fibers and thereby counteracting the tendency of cleaving the wooden workpiece into which the screw is threaded. The splitting forces of the wood which might result in a loss of retention of the screw are reduced by the cuts being made.
The thread in the finless terminal portion of the tip of the screw makes sure the screw is drawn into the workpiece firmly at the onset when it is threaded especially into wooden material. This is not impeded by the cutting edges as they do not begin to become effective before a certain minimum depth of penetration into the wooden workpiece has been reached.
Although theoretically the angle of inclination of the fins with respect to the longitudinal axis of the screw, ultimately, may reach zero value, the fins with their cutting edges preferably are disposed at an angle of inclination greater than 5&phgr; in terms of amount with respect to the longitudinal axis of the screw. The best cutting effect is obtained if the fins have a left-hand twist, in other words if they become effective over the full length of the cutting edges as they are being screwed in. The length of the fins may end at the transition between the shank and the tip. Yet it may also extend farther beyond and over part of the shank. In either event the height of the fin surpasses the core diameter of the screw so that the diameter as measured across the fins at the transition between the tip and the shank portion always is greater than the core diameter of the shank portion.
Advantageously, fins with cutting edges according to the invention may be provided also in the area where the thread terminates towards a threadless shank portion or towards the head of a screw.
With the screw according to the invention the thread pitch is greater than it is with conventional wood screws. The pitch angle of the thread preferably lies in the range between 16° and 20°, especially at about 19°.
The screw according to the invention can be threaded without any advance boring into wood, especially softwood but also into other material, such as chip boards.
REFERENCES:
patent: 1084643 (1914-01-01), Lasater
patent: 4323326 (1982-04-01), Okada
patent: 4878793 (1989-11-01), Hewison
patent: 5273383 (1993-12-01), Hughes
patent: 5895187 (1999-04-01), Kuo-Tai
patent: 6000892 (1999-12-01), Takasaki
Carter, Ledyard & Milburn
Ludwig Hettich & Co.
Saether Flemming
LandOfFree
Screw with cutting edge does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Screw with cutting edge, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Screw with cutting edge will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2587040