Note: Descriptions are shown in the official language in which they were submitted.
2~2~6~
IMPRaV~ SCREWDRIVER Brr FOR PHILLIPS-HE~D FASTENERS
Background and Summary of the Invention
The present invention relates to screwdriver bits and in
particular to an ill~LUV~d screwdriver bit for Ph;ll;ps-head fasteners
that significantly reduces the "cam-out" experienced with a
c~l.ven~ional screwdriver bit for Phillips-head fasteners.
C~l~v~-~ional Phillips-head fasteners and screwdrivers were
originally developed to provide a fastening system that would
facilitate efficient installation of fasteners on an assembly line.
In particular, as compared to conventional slotted screws, the
ph; 11 ;ps screw was designed to center quickly and easily on the
screwdriver and permit more torque to be applied to the screw so that
it would hold tighter than conventional slotted æ rews. In addition,
it was expressly contemplated that, when applied by auL~,~Led
screwdrivers on an assembly line, the increasing torque applied to the
Phillips screw would eventually cause the driver to pop out of the
recess in the æ rew. In other words, the original Phillips-head
design was intended to cause cam-out of the driver without damaging
the screw head. It is, of course, this tendency of the Phillips-head
design to cause cam-out of the driver, that is a principal source of
irritation for craftsmen and ordinary consumers alike.
It is, therefore, the primary object of the present
invention to provide an ill~Loved screwdriver bit that satisfies
standard Phillips-head y~l~LL~ and, therefore, is useable with
standard Phillips-head fasteners and yet is designed to significantly
reduce the tendency of the driver to cam-out of the recess in the
screw head.
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In addition, it is an object of the pLesenL invention to
provide an ill~loved driver for Ph; 11 ip5-head screws that enables the
application of significantly greater torque loads to a standard
Ph;ll;ps-head screw with munimum distortion of the shape of the recess
in the screw head.
Fur~henmnre, it is an object of the present invention to
provide an il,~o-ved driver for Ph;ll;ps-head screws that enables the
application of significantly greater torque loads to a standard
Ph;ll;ps-head screw equally in both rotational directions.
Additional objects and advantages of the present invention
will beoome apparent from a reading of the following detailed
description of the preferred embcdiment which makes reference to the
drawings in which:
Brief Description of the Drawings
Figure 1 is a side elevational view of a standard
screwdriver bit for Ph;ll;~s-head screws;
Figure 2 is an end view of the Ph;ll;ps bit shown in Figure
l;
Figure 3 is a sectional view taken along line 3-3 in Figure
2;
Figure 4 is a partial sectional view taken along line 4-4 in
Figure 3;
Figures 5 - 11 comprise a progressive series of sectional
views of a standard Ph;ll;ps-type bit and screw fastening system
starting from the base of the wings of the screwdriver bit in Figure 5
to the top of the head of the fastener in Figure 11;
6~
Figure 12 is a side elevational view partially in section of
a standard Phillips fastening system;
Figure 13 is a force vector diagram illustrating the cam-out
force o~.~unen~ generated by the standard Ph;llips fastener system;
Figure 14 is a sectional view of a standard Phillips
fastener system illustrating the deformation of the recess in the head
of the fastener;
Figure 15 is a enlarged view of one of the outer radial wing
sections shown in Figure 14;
Figure 16 is a side elevational view of a Phillips-type
screwdriver bit according to the present invention;
Figure 17 is a simplified perspective view of the bottom end
of the bit shown in Figure 16;
Figures 18 - 24 comprise a progressive series of sectional
views of the Phillips-type fastening system according to the present
invention frcm the base of the wings of the screwdriver bit in Figure
18 to the top of the head of the fastener in Figure 24;
Figure 25 is an enlarged view of one of the wing sections of
the Phillips-type fastening system according to the present invention;
Figure 26 is a sectional view similar to Figure 24 showing
the screw~river bit applying maximum torque to the fastener;
Figure 27 is a side elevational view partially in section of
the Ph;ll;ps-type fastening system according to the present invention;
Figure 28 is a force vector diagram illustrating the cam~out
force cnmr~nP~t generated by the Ph;ll;ps-type fastener system
according to the ~.es~,~ invention; and
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Figure 29 is an enlarged side elevational view partially in
section of one of the wing sections of the Ph;llirs-type fastening
system according to the present invention.
Detailed Description of the Preferred Embodiment
The structure, significance, and advantages of the present
invention are believed best understood if described in relation to a
standard Phillips screwdriver bit. Acoordingly, Figure 1 in the
drawings illustrates a standard No. 2 Phillips bit 10 and will be used
as a starting point for the description of the present invention. A
standard Ph;ll;~s bit lO has a cross-shaped tip that is formed through
the creation of four wedge.-shaped concave recesse.~ that converge
toward the tip 11 of the bit. m e recesses define four evenly spaoe d
wings 12 that are tapered along their outer radial surfaces 14 toward
the tip of the bit. The angle of this taper is referred to as the
"wing angle" and in a standard No. 1, 2, or 3 Phillips bit is equal to
26 degrees 30 minutes relati~e to the vertical axis of the bit. Ihe
radially ;nnPrmnst part 16 of each recess is referred to as the "root"
16 and the angle at which the root diverges from the tip relative to
the axis of the bit is referred to as the "root anglen. In a standard
No. 2 Ph;ll;~s bit, the root angle of that portion of the bit 10
adapted to engage the fastener is 5 degrees 45 minutes, as shown in
Figure 3. m e root angle in a standard No. 3 Ph;lll~s bit is also 5
degrees 45 minutes; however, the root angle is 7 degrees in a standard
No. 1 Phillips bit. A~dition, as best illustrated in Figure 4, the
angle formed by the adjoining interior wing surfaces 18, referred to
as the "included angle", is 92 degrees in a standard No. 1, 2, or 3
2QOZ162
Phillips bit and remains constant along the entire axial length of the
bit wings 12. Finally, the tip 11 of a standard Phillips bit is
con;~Ally shaped as shown in Figure 1 to form a point, the conical
surface diverging from the point at an angle of 19 degrees relative to
the plane normal to the axis of the bit. The specifications and
dimensions for standard Ph;ll;~s-type bits are defined in literature
published by the Screw Research Association.
Given the above ~ Lly for a standard Phillips bit 10, it
is important to bear in mind, as shown in Figures 5 - 11, that the
cross-shaped recess 20 formed in the head 22 of a standard
Phillips-head fastener 24 is created with a punch having precisely the
same dimensional characteristics. Accordingly, the standard Ph;ll;~s
screwdriver bit 10 is adapted to fit precisely into the recess 20
formed in the head 22 of a standard Phillips fastener 24, except for a
designed-in toleran oe clearance which enables the bit to fit readily
into the recess 20. This relationship is clearly demonstrated in
Figures 5 - 11 which comprise sectional views of a standard
Phill;~s-type fastening system progressing in the axial direction from
the base of the bit wings 12 in Figure 5 to the top of the head 22 of
the fastener 24 in Figure 11.
In view of the precise conformity between the driver lO and
the recess 20 in the head 22 of the fastener in a standard
Phi 11 ;ps-type fastening system, it will be appreciated that as the
screwdriver bit 10 is rotated in the clockwise direction, torque is
applied to the head 22 of the fastener 24 along the outer radial edges
18 of the bit wings 12, as indicated by the arrows appearing in
Figures 5 - 11. miS occurs due to the simple geametric fact that the
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points far~hest from the center of rotation move the greatest
distance. Therefore, assuming a substantially unifonm tolerance gap
between the bit 10 and the recess 20, the outer radial edges 18 of the
bit wings 12 will take up the tolerance gap first and engage the
opposing outer recess wing surfaces, establi~h;nq lines of contact
therealong. The con~ LLcLion of torque along the outer radial edges
18 of the bit wings 12 results in the recess wings 21 in the head 22
of the fastener 24 defonming in these areas as torque levels increase.
This deformation is illusLL~ed in scmewhat exaga~erated form in
Figures 14 and 15. Once this deformation occurs, the radially outward
facing end surfaces 14 of the bit wings 12 came into contact with the
newly formed opposing surfaces 26 in the deformation areas, thereby
generating a significant force in the vertical direction (i.e., out of
the paper relative to Figures 14 and 15) causing the driver 10 to "cam
out" of the screw-head recess 20.
This phenamenon is illustrated and the related force vectors
dia~r~l~d in Figures 12 and 13. In particular, as the torque applied
along the outer radial edges 18 (Figure 11) of the bit wings 12
increases and deformation of the outer radial areas of the recess
wings 21 occur, a force is generated by the radially outward facing
end surfaces 14 of the bit wings 12 against the deformed surfaces 26
of the recess wings 21 in a direction normal to the end surfaces 14,
as indicated by the arrows 27 in Figure 12. This, in turn, creates an
equal and opposite force from the deformed surfaces 26 against the
radially outward facing wing surfaces 14. This opposing force,
designated "Z~l in the force diagram illusLLaLed in Figure 13 is
comprised of a horizontal for oe r~ n~nL, designated "X", and a
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2002162
vertical force component, designated "Y". Given the
Phillips-stan~Ard wing angle of 26 degrees 30 minutQs, the
resulting cam-out force, "y-l, generated by the
application of torque ~rom the screwdriver blt lO to the
fastener 24 is equal to a factor of 0.43 (i.e., sin
26-30') times the magnitude of the force vector "~-. In
other words, the greater the application of torque, the
greater the force t~nd1~g to cam the screwdriver bit lO
out of the recess 20 in the head 22 of the fastener 24.
To obviate this cam-out tendency of the stAn~rd
Phillips fasten~g system, the improved Phillips-type
screwdriver bit according to the present invention has
been designed so that torque loading between the bit and
the recess in the head of a standard Phillips fastener is
confined to the side faces of the bit wings. This is
accomplished in the manner described below. Referring now
to Figures 16 and 17, an improved Phillips-type
screwdriver bit 30 according to the present invention is
shown. At the outset it should be noted that the present
screwdriver bit 30 retains the same root angle (either 5
degrees 45 minutes for a no. 2 or No.3 Phillips fastener,
or 7 degrees for a No. l Phillips fastener) and
eubstantially the same wing angle of 26 degrees 30 minutes
according to standard Phillips specifications to ensure
that the present bit 30 is fully compatible with standard
Phillips-head fastenere. However, as will become apparent
to those skilled in the art, to ensure compatibility with
etandard Phillips fasteners, it is only necees~ry that the
screwdriver bit according to the present invention
possesses a root angle and wing angle approximately equal
to but not substantially greater than (within limits) the
standard Phillips dimensions. Thus, it will be
appreciated that the present invention does not reguire a
uniquely configured fastener to achieve its increased
torque loading capabilities. Moreover, due to the radial
symmetry of the present ecrewdriver bit 30, the increased
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torgue loading capabilities of the present invention apply
equally in both rotational directions of the driver.
Returning to the drawings, it will be noted from an
examination of Figure 16 that the width of the radially
outward facing surface 34 of the bit wing 32 remains
substantially constant from the base 31 of the wing to the
wing tip 35. This is contrary to the configuration of a
standard Phillips bit, as illustrated in Figure 1, whose
corresponding surface 14 gradually increases in width from
the base 11 of the wing 12 to the wing tip 15 due to the
geometry of the Phillips-stAn~rd root angle and the
constant Phillips-stAn~Ard included angle. Specifically,
the improved Phillips-type bit 30 according to the present
invention does not maintain a constant included angle
from the base 31 of the wing 32 to the wing tip 35,.
Rather, as illustrated in Figure 17, the included angle
between the bit wings 32 in the present screwdriver bit 30
is equal to the Phillips-standard 92 degrees at the base
31 of the bit wings 32 and progressively increases to
approximately 105 degrees at the wing tips 35. In other
words, rather than the side surfaces of the bit wings 12
being defined by flat planes as in the ~tAndArd Phillips
bit 10, the side surfaces of the bit wings 32 in the
present bit 30 comprise generated surfaces. Therefore, as
used herein and in the claims, the term "generated
surface" refers to the non-planar, curved surface
characteristic of the bit wing sidewalls that results from
the varying included angle between ad; oining bit wings
32. This is demonstrated in FIG. 17. In the embodiment
illustrated in FIG. 17 the included angle between the bit
wings 32 is equal to the Phillips-stAn~Ard 92 degrees at
the base 31 of the bit wings and p~oy~essively increases
to approximately 105 degrees at the wing tipg 35. As a
result, when the screwdriver bit 30 according to the
present invention is inserted into the recess 20 of a
standard Phillips-head fastener 24, a gradually increasing
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gap 38 (Figure 25) is defined between the blt wlngs 32 and
the recess wings 21 in the radially outward direction.
This is due to the fact that the thic~ne~ of the recess
wings 21 in the stAn~rd Phillips-head f~stener 24
diminishes more gradually in the radially outward
direction due to the constant Phillips-stAnAArd included
angle, which becomes progressively smaller than the
increasing included angle of the present bit 30. In other
words, the gap 38 ehown in Figures 24 and 25 results from
the fact that the included angle between the sidewalls of
the recess wings 21 corresponds to the Phillips-stAn~rd
92 degrees whereas the included angle between the bit
wings 32 at this illustrated axial position of bit 30
co~Le~onds to approximately 103 degrees. (Note that the
103-degree angle referred to corresponds to the included
angle at an axial position somewhat below the wing tip 35
as the entire bit portion typically does not fit into the
recess 20 in the head of the fastener 24, as shown in
Figure 27.) In addition, it is important to note that the
radial dimension of the bit wings 32 when the bit is fully
inserted into the recess 20 is less than that of the
recess wings 21 so that a slight space is maintained
between the radially outward facing surfaces 34 of the
bit wings 32 and the opposing surfaces 44 of the recess
wings 21. In the preferred embodiment of the present
invention, the roots 36 of the recesses between adjoining
bit wings 32 are also formed somewhat ~eerer so that an
additional gap 40 (Figure 25) is created between the root
36 of the bit 30 and the root 42 of the recess 20 in the
standard Phillips-head fastener 24. It has been earlier
noted that the radially outwardly facing surfaces 34 of
bit wings 32 taper toward a common point. It is further
noted here that the thickness of the bit wings 32 adjacent
the roots of these wings increases gradually in the axial
direction away from this common point. This relationship
follows from the fact that the root angle of the bit 30 ~s
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compatible with the Phillips-~tandard root angle.
Finally, as illustrated in Figures 16 and 27, the base 31
of the present screwdriver bit 30 i8 preferably truncated
as shown to prevent the bit 30 from bottoming out when
in~erted into the recess 20 of a st~n~rd Phillips-head
fastener 24.
As a result of this configuration, when the present
screwdriver bit 30 is inserted into the recess 20 of a
stAn~Ard Phillips-head fastener 24 and rotated in a
clockwise direction, torque is applied to the fastener 24
along lines of contact 46 between the side surfaces of the
bit wings 32 and the opposing side surfaces of
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2C~0~1~Z
the recess wings 20, as indicated by the arrows appearing in Figures
18 - 24. In addition, it will be appreciated that these initial lines
of contact 46 between the side surfaces of the bit wings 32 and recess
wings 20 are essentially parallel to the root 36 of the bit 30, as
illustrated by the dashed lines in ~igure 27. In other words, these
lines of contact 46 form substantially the same 5-degree 45iminute
angle with respect to the axis of the bit 30 corresponding to the
Ph;ll;rs-standard root angle. Moreover, as the level of applied
torque increases and the bit 30 begins to deform the recess 20, the
lines of contact expand radially outwardly in parallel fashion along
the side faces of the bit wings 32, as indicated by the shaded portion
50 illustrated in Figure 29. m is serves to significantly increase
the level of torque that can be transmitted from the screwdriver bit
30 to the fastener 24 while confining the areas of engagement to the
side surfaces of the bit wings 12. This distinction between the
present invention and the standard Phillips bit is illustrated in
Fig~lres 14 and 26.
Significantly, the deformation of the recess 20, as
illustrated in Figure 26, along the sidcwPll~ of the recess wings 21
d oe s not add to the relatively small cam-out forces generated by the
application of torque along the initial lines of contact 46 between
the bit 30 and recess 20. Accordingly, driving eny~ nL between the
screwdriver bit 30 and the fastener 24 can easily be maintained with
the application of a modest amount of downforce. m is ph~ l of
the present invention is illustrated and diay~ d in Figures 27 and
28. As previously noted, the application of torque from the bit 30 to
the fastener 24 along the initial lines of contact 46 on the side
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surfaces of the bit wings 32 is represented by the dotted lines in
Figure 27. m e ap~lic~tion of force in this manner results in the
generation of an outwardly directed force c~l~onenL perpendicular to
the lines of contact, as indicated by the arrows 45 in Figure 27.
m is, in turn, results in the generation of an equal and opposite
force vector designated "Z" in the ~ccnmr~ying vector force diagram
shown in Figure 28. In view of the a~lo~imated 5-degree 45iminute
angle of the for oe ~Lol "Z" relative to the axis of the bit 30, the
for oe vector "Z" is oamprised ~led~,linantly of a horizontal force
component, l~hple~ "X", and a relative small vertical force component,
labeled "Y". In fact, the vertical force cYxnponent "Y" tending to
cause the bit 30 to cam-out of the re oe ss 20 is only equal to
approximately a factor of 0.10 (i.e., sin 5 45') times the magnitude
of the force vector "Z". Accordingly, when compared to a standard
Ph;]l;ps bit 10, significantly less downward force is required from
the O~e~a~Or to retain the present bit 30 in the recess 20 of a
standard Phillips-head fastener 24, even at high levels of applied
torque.
From the above discussion, it will be appreciated that the
screw~river bit 30 according to the present invention is able to
significantly reduce the cam-out for oe associa~ with a standard
Ph;ll;ps screwdriver bit 10 by ~ ~.Ling the radially outward facing
bit wing surfaces 34 from contacting the re oe ss 20 in the head 22 of
the fastener 24. Due to the angle of these bit wing surfaces 34, the
application of foroe along these surfa oe s is believed to be the
greatest cause of cam-out in a standard Phillips design. m erefore,
the present screwdriver bit 30 is capable of deforming the recess
--11--
20~ Z
wings 21 in a Phillips-head fastener 24 to the degree illustrated in
Figure 26 before significant cam,out forces will be ~neLa~ed. At the
stage illustrated in Figure 26, torque is being applied along
virtually the entire side surfaces of the bit wings 32 from the
initial lines of contact 46 adjacent the root 36 of the bit to the
outer radial edges 48 of the bit wings 32.
Finally, it will be appreciated that, in view of the
radially symmetrical design of the invention, the present screwdriver
bit 30 is capable of applying significantly greater torque loads than
a stan~rd Phillips bit in either r~tational direction. m erefore,
unlike certain existing modified Phillips designs which radially
offset the bit winas and are, therefore, primarily useable in only one
rotational direction, the present invention is equally useful for
tightly setting standard Philips screws and for "breaking free" and
removing "frozen" Phillips fasteners.
While the above description constitutes the preferred
~mha~;m~nt of the invention, it will be appreciated that the invention
is susceptible to dification, variation, and change without
departing from the proper scope or fair mPAn;ng of the Acc~mpAnying
claims.
