Tools – Wrench – screwdriver – or driver therefor – Having work engaging and force exerting portion inserted...
Reexamination Certificate
2000-08-23
2002-04-30
Smith, James G. (Department: 3723)
Tools
Wrench, screwdriver, or driver therefor
Having work engaging and force exerting portion inserted...
C411S404000
Reexamination Certificate
active
06378406
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a driver bit and a screw for use therewith. More particularly, it relates to a combination of a driver bit and a screw fitting the driver bit which combination effects tight mating of crossed flutes or bit mate flutes formed on the screw head portion and the driver bit fitting the flutes and always enables quick positive screwing and unscrewing by transmission of appropriate torque.
BACKGROUND ART
Conventionally known are the combinations of typical screws and driver bits as shown in
FIGS. 13
to
16
. That is,
FIGS. 13 and 14
show a conventional screw with crossed flutes;
FIG. 15
shows a driver bit for use with the screw with crossed flutes; and
FIG. 16
shows the aforementioned screw and driver bit, mated with each other.
A prior art screw
10
shown in
FIG. 13
is provided, on a screw head portion
10
a
thereof, with crossed flutes
12
. The crossed flutes
12
are provided with constantly inclined flute portions
12
a,
each extending from the end portion towards the central portion of a screw neck portion l
0
b.
The crossed flutes
12
are also provided, on a bottom portion thereof, with a substantially conical bottom surface
14
inclined gradually. Incidentally, reference numeral
13
designates tapered sidewall portions formed between adjacent crossed flutes
12
. That is, the tapered sidewall portions
13
engageably contact with the blade portions of a driver bit, which is described later. In addition, at the corners adjoining the respective inclined flute portions
12
a,
tapered coupling surfaces
17
a,
17
b
are formed which extend from the position of the conical bottom surface
14
to the opening rim portions of the crossed flutes
12
on the screw head portion
10
a.
These tapered coupling surfaces
17
a,
17
b
are also adapted to engageably contact part of the blade portions of the driver bit, which is described later.
On the other hand, a prior art driver bit
20
shown in
FIG. 15
is provided with blade portions
22
to fit the crossed flutes
12
of the aforementioned screw
10
. The driver bit
20
is also provided with extended blade portions
22
a
each extended so as to fit the shape of the inclined flute portions
12
a
that are formed to orient towards the central portion of the screw neck portion
10
b
from the end portions of the aforementioned crossed flutes
12
. Incidentally, reference numeral
23
designates tapered sidewall portions that are formed on the both sides of the aforementioned respective blade portions
22
or extended blade portions
22
a.
That is, the tapered sidewall portions
23
engageably contact with the tapered sidewall portions
13
formed in the crossed flutes
12
of the aforementioned screw
10
.
According to the combination of the prior art screw and driver bit formed as such, when the screw
10
and the driver bit
20
are fit to each other as shown in
FIG. 16
, the blade portions
22
of the driver bit
20
and extended blade portions
22
a
fit into the inclined flute portions
12
a
of the crossed flutes
12
, respectively, as described above. The sidewall portions
23
of the aforementioned blade portions
22
and extended blade portions
22
a
are brought into contact with the tapered sidewall portions
13
of the crossed flutes
12
of the screw
10
. Thus, rotating the driver bit
20
allows a predetermined torque to be transmitted to the screw
10
. That is, screwing and unscrewing can be achieved on a desired target object to be screwed.
However, according to the combination of the prior art screw
10
and the driver bit
20
formed as described above, the crossed flutes
12
of the screw head portion
10
a
form constantly inclined flute portions
12
a
orienting towards the central portion of the screw neck portion
10
b
from the end portions thereof. On the other hand, for the driver bit
20
corresponding thereto, the ridge portions of the extended blade portions
22
a
fit the shape of the aforementioned inclined flute portions
12
a
to fit into the aforementioned crossed flutes
12
. Moreover, the ridge portions of the extended blade portions
22
a
are made wider gradually backwards from the distal end portion thereof. Furthermore, the tapered sidewall portions
23
formed on the respective blade portions
22
of the driver bit
20
are also engageably brought into contact with the tapered sidewall portions
13
formed in the crossed flutes
12
of the screw
10
. Accordingly, since the aforementioned driver bit
20
and the crossed flutes
12
can be said to be totally in taper contact with one another, rotating the aforementioned driver bit
20
in a predetermined direction causes the distal end of the driver bit
20
to fly outwardly along the inclined surface of the inclined flute portions
12
a
of the aforementioned crossed flutes
12
(shown by an arrow in FIG.
16
), resulting in the so-called “come-out phenomenon”.
In particular, as shown in
FIG. 14
, the shape of the crossed flutes of a prior art screw is formed in such a manner that the respective crossed flutes
12
are made relatively larger in width than the ridge portions of the extended blade portions
22
a
of the driver bit
20
in order to facilitate mating the distal end of the driver bit
20
with the crossed flutes. On the other hand, the area of the tapered sidewall portions
13
and the tapered coupling surfaces
17
a,
17
b,
formed at a boundary portion or corner portions between adjacent crossed flutes
12
,
12
, is relatively small. Accordingly, rotating the aforementioned driver bit
20
causes a great amount of stress to be loaded on the aforementioned tapered sidewall portions
13
and the tapered coupling surfaces
17
a,
17
b.
Thus, as shown in
FIG. 14
with shaded portions
15
, great fastening resistance would cause the aforementioned tapered sidewall portions
13
and the tapered coupling surfaces
17
a,
17
b
to be gradually damaged. Therefore, an increase in the damaged portions (the shaded portions
15
) would make the come-out phenomenon to occur frequently in the aforementioned driver bit
20
, making it impossible to effect screwing.
From these points of view, it is necessary to apply thrust to the driver bit
20
to strongly press the bit against the flute portions
12
a
at the time of rotating the driver bit
20
in order to prevent the come-out phenomenon in the aforementioned driver bit
20
. However, pressing the bit as such would cause screwed target objects, particularly such as precision parts, to be broken or damaged although no problem will occur if the target objects are rigid bodies such as meal.
In addition, the occurrence of the aforementioned come-out phenomenon would cause the distal end portion of the bit or the blade portions
22
and extended blade portions
22
a
to be worn quickly. The wear would cause the aforementioned come-out phenomenon to occur more frequently, resulting in an increase of the damage of the screw flutes.
Furthermore, applying an excessive thrust to the aforementioned driver bit
20
could be useful to prevent the aforementioned come-out phenomenon. However, this would make it impossible to transmit precise torque to the screw, and thus operators would apply different amount of thrust to the driver bit
20
. Consequently, torque for fastening screws would become greatly different from operator to operator.
Still furthermore, when tapping screws are screwed into a target object made of synthetic resin or the like, friction caused by the thrust would be added to that by the rotation of the screw. This would cause a great amount of heat to be produced to such an extent as to reduce the hardness of the screwed portion of the target object, thereby causing the screw to become loose or the target object to be damaged.
On the other hand, when screwing is carried out manually, rotating the driver bit
20
while sufficiently pressing the driver bit
20
against the screw would require a great amount of effort of the operator and make the operator exhausted.
In addition, according to the combination of the afor
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Smith James G.
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