Tools – Wrench – screwdriver – or driver therefor – Having work engaging and force exerting portion inserted...
Reexamination Certificate
1999-11-16
2001-07-03
Smith, James G. (Department: 3723)
Tools
Wrench, screwdriver, or driver therefor
Having work engaging and force exerting portion inserted...
C411S404000
Reexamination Certificate
active
06253649
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a screw with a recessed head and also relates to a driver bit capable of engaging with the recessed head of the screw, wherein the head has a cruciform recess for receiving a torque from the driver bit.
2. Prior Art
Phillip's crossing recesses have been employed in many countries as the recesses to be formed in some types of screw heads, and now have spread worldwide. Those screws with such prior art recessed heads afford sure transmission of torque by virtue of their crossing recesses. The driver bits can fit in the recesses snugly and firmly, thereby improving operation efficiency in tightening or removing those screws.
It is however noted that there have arisen certain problems in cases wherein some quenched and hardened self-tapping screws or self-drilling screws had been involved. These screws usually require stronger thrust when tightened. The crossing recesses widely adopted have in general their bit-sticking regions that are disposed near the centers of said recesses, so that thrust is born merely with smaller areas. A strong bending moment produced from the tightening torque is thus imparted mainly to such a small area in each recessed head. Those heads of the exemplified screws have however so hard heads that the driver bits' recess-sticking portions have been abraded early and seriously, causing a less reliable sticking engagement of the driver bits with the recessed heads. There has been a further problem that motor-driven or otherwise automatic screw drivers have often encountered breakage and/or cam-out of their bits, due to an over-torque that in turn has been caused by inexpert operators.
In order to resolve the problems inherent in the prior art, some proposals have been made to employ sophisticated recesses in place of such simply crossing ones of the screw heads, with driver bits also being modified to match the sophisticated recesses. The proposed recesses in the screw heads are suited to transmit a higher torque (as disclosed for instance in the Japanese Patent Laying-Open Gazette No.3-292407, Japanese Patent Publication No. 737805 and the U.S. Pat. No. 5,020,954).
SUMMARY OF THE INVENTION
An object of the present invention that was made in view of the background discussed above is therefore to provide a screw with a recessed head and a driver bit therefor, such that a recess in the head is of a cruciform shape simply modified but nevertheless adapted to transmit a stronger torque and affording a larger sticking area resistant to a stronger thrusting stress.
In order to achieve this object, the crossing recess formed in a top of the screw head consists of a central region and four grooves extending radially from and continuing from said region to thereby surround it, such that each groove is tapered to reduce its width towards a conical bottom disposed in radial direction away from the central region. Each groove is defined with opposite side walls facing one another and transmitting torque and with the conical bottom, which connects outer edges of the side walls to each other. Width ‘A’ of the said conical bottom is made larger than the corresponding width ‘a’ of the conical bottom of each groove formed in the prior art widely-used standard crossing recesses of the same groove length ‘M’. The crossing recess of the invention is characterized in that length (or depth) ‘B’ in radial direction of the side walls is made smaller than the width ‘A’. Distance ‘C’ between inner edges each defined as the juncture of adjacent side walls respectively belonging to the adjacent grooves is at least the product of 1.5 and the width ‘A’. The crossing recess is also characterized in that one of the side walls of each groove lies in a flat plane extending in parallel with an axis of the screw, with the one side wall being located forward with respect to a direction in which the screw will be tightened. The conical bottom of each groove is preferably slanted at an angle of about 5 degrees relative to the screw axis so as to provide a conical sticking surface.
Alternatively, the other side wall located rearward in the direction of tightening the screw may be slanted at an angle of about 10 degrees relative to the screw axis. Such other side walls will also form a flat sticking surface substituting the conical one, also achieving the same object set forth above.
The driver bit also provided herein has a tip end matching the central region of the crossing recess and four protrusions (viz., drive vanes) extending from an outer periphery of the tip end and matching the four grooves in the recess.
When tightening the screw of the invention, the driver bit specially designed herein to match the screw has to be used. However, when loosening for the purpose of maintenance or disassembly, any conventional cruciform or square-columnar driver bit may also be used instead of that provided herein.
REFERENCES:
patent: 2173707 (1939-09-01), Brown
patent: 2397216 (1946-03-01), Stellin
patent: 4084478 (1978-04-01), Simmons
patent: 4089357 (1978-05-01), Gill
patent: 4202244 (1980-05-01), Gutshall
patent: 4355552 (1982-10-01), Gutshall
patent: 4464957 (1984-08-01), Gill
patent: 4998454 (1991-03-01), Chaconas et al.
patent: 5020954 (1991-06-01), Dreger
patent: 5120173 (1992-06-01), Grady
patent: 5641258 (1997-06-01), Sala
Antonelli Terry Stout & Kraus LLP
Smith James G.
Thomas David B.
Yugenkaisha Shinjo Seisakusho
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