Note: Descriptions are shown in the official language in which they were submitted.
2~
BACKGROUND O~ THE INVENTION
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l. Fleld of the Invention
The present invention relates to tools that are used
to turn fasteners having polygonal sided sockets. In particular,
the present invention relates to tools having a rounded head,
thereby having the capability of turning such fas-teners in a
non-coaxial relationship.
2~ Description of the Prior ~rt
The previously known prior art contains several tools
that have a rounded or a circular head used to turn fasteners
that have polygonal sockets or recesses. The purpose of the
rounded head is to provide the capabili~y of turning the
fastener in an angular relationship with respect to the
fastener's axis. This capability is important where the
fastener is located in a hard to reach place. In this situation
it is necessary to insert the tool and turn it through a partial
turn, then withdraw the tool and reinsert it into the socket,
and go through another partial turn, and so on, wasting both
time and effort.
The prior art, in attempting to solve this problem,
has approached several limitations. The first limitation is
the angle with respect to the axis of the fastener in which
the tool can be used to turn the fastener without binding the
fastener. British patent No. 548,615 shows a hex wrench with
this limitation. Figure l displays at how small of an angle
the hex wrench is able to engage the socket without binding.
This is due to the nature of the curvature of the ball head.
In an effort to enable~even this small an angle of tilting
to take place, the neck is made relatively small in diameter.
One advantage of uslng hex wrenches is~ their ability to with-
stand great àngular forces without twisting. In forming the ~ -
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neck portion, the inherent strength of the wrench can be
compromised if the neck portion is made too small in diameter.
Manufacturin~ a tool with a small neck diameter risks the
chance of the head being twisted off under great force.
British patent No, 876,781 shows a tool in Figure 1
that circumvents the proble~ o~ binding by providing a certain
amount of play "between the ball-shaped head and the socket".
This is evident from Figure 2 This, however, tends to increase
the chance of the edges of the ball becoming rounded when sub-
stantial ~orces are applied to the tool to cause the tool to
slip with respect to the socket~
U, S. patent No. 3,940,946 shows a universal ]oint
with a head portion larger than its sha~t. This prevents the
use of standard polygonal stock. In order to use standard
polygonal stock, the head can be no larger than the shank or
shart. Furthermore, the sides of the head are not of uniform
width. While this mlght be satisfactory with a universal joint
where the head and socket can be matched, it would preclude the
use of a head of this type as an element of a wrench where the
wrench must be used with standard socket types of screw fasten-
ers. Moreover, the patentee depends upon the use of an elasto-
meric material over the head to prevent binding in the socket.
U. S. patent No. 4,080,079 shows a universal joint
in which the sides are arcuately curved with substantially
the same radius as the radius oE the ball portion. As will be
pointed out later in the specification, this does not result
in the maximum amount~of tiIting for a given shank size.
3. Summary of th~e_Invention
The present invention includes a tool with a poly-
~onal cross section havlng an~integral drive shank portion, aneck portion, and a drive hend portion in a coaxial relation-
ship along a central axis. The curvature of the drive head
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portion is especially clesigned to permit the maximum amount of
tilting of the tool without binding as i-~ is turned, while at
the same time providing a relatively thick neck portion. This
is accomplished by providing the head portion with curved sides
corresponding to the same number of sides as the shank portion,
with the center of curvature of the surfaces of the curved
sides being displaced outwardly from the longitudinal axis of
the tool so that the curved sides substantially conform to a
portion of an ellipse. The surface of the neck portion may
take a variety of forms but is preferably in the form of an
inwardly curved surface of revolution whose axis of revolution
lies along the central axis of the tool.
The curved sides of the head portion substantially
conform to the end portions of an ellipse whose minor axis lies
along the central axis of the tool. The major axis of the
elliptical sides has a pair of foci wherein the distance from
the minor axis to each focus is defined substantially by
1/2 D (l-cos ~) wherein D is the distance between opposed sides
of the tool and ~ = _ 360 . The distance from
2 tNo. of sides)
each focus to the nearest intercept of the major axis with the
end portion is defined further by the equation 1/2 D cos ~.
The neck portion which is defined by an inwardly
curved surface of revolution is tangential to the elliptical
surface of the head portion at the point of confluence.
~5 Since the head portion can be of the same diameter
as the shank, the tool of the present invention can be manufac-
tured from the same stock as tools~not having the elliptical
head portion. This construction, of course, eliminates the
extra cost that results in having specially formed pieces of
steel in order to accommodate a larger head portion.
4. Brief Description of the Drawing
Figure 1 is a side elevational view showing the tool
of the present invention engaging a hex socket screw;
~2~
Figure 2 is a perspective view of -the tool;
Figure 3 is a closeup side view of the tool;
Figure 4 is an end view of the head portion; and
Figure 5 is a side view that shows the geometrical
requirements of the surfaces of the present invention.
5. Detalled Description of the Preferred Embodiment
In Figure l, the tool of the present invention in the
preferred form of a hex wrench is shown yenerally at lO. Tne
hex wrench lO is shown engaging screw 12 in angular relationship
indicated by the angle ~ .
The hex wrench includes a drive shank portion 14, a
neck portion 16 and a drive head portion 18, as best seen in
Figures l, 2 and 3. The preferable cross section configuration
of the hex wrench is an equilateral hexagon, as shown in Figure 4.
The drive head portion 18 has sides 20 with elliptical
surfaces 22. The elliptical surfaces 22 substantially conform
to the end portions of~an ellipse whose minor axis 26 lies along
the central axis 27 of the wrench lO. The ellipse defining the
elliptical surfaces has two foci Fl and F2, as shown in Figure 5,
and a midpoint 28 defined by the intersection of the major axis
24 and the minor axis 26.
The shape of the ellipse definlng the surfa:ces 22 of
the side 2Q;of the head portion 18 is~a functlon of the number
of sides of the wrench., The number:of:sides 20 is expressed in ~.
degrees by the fol}owing: ~ = 2 (N-o of sIdes) The dngle
determines the distance from the~midpoint 28~to the foci and
: the distance from~each focus to an intercept 29 of the ma~or
axis with the surface 22. In~this manner~ the number of sides
as expressed in ~ determines the shape of the elliptical
surfaces 22.
The relationship is explqined by~an understanding
of an el;lipse. In a circle the~ foci Fl and F2 are at the mid-
. :
.
x = . .
- .. . .
point of the major and minor axes. ~s the circle turns, F
and F2 proceed on the vertical axis, the major axis in an
ellipse, away from the midpoint ~8. Fl and F2 will proceed
along the major axis as the circle turns until the circle turns
9Q and ~1 and F2 become the vertical intercepts 29 and the circle
a flat line Thus~ Fl and F2 are some function of the angle
as shown in Figure 4 since ~ is the angle that the circle is
tuxned to- form an ellipse. From this understanding, the dis~ance
from a focus, Fl or F2, to the nearest intercept along the
major axis is deflned by 1/2 D cos ~, where D is the distance
from one side to an opposing side or as in the preferred
embodiment, the width of the hex wrench.
Since the distance from the midpoint 28 to an inter-
cept 29 along the major axis is constant, the distance from the
midpoint to either focus Fl or F2 is deined by 1/2 D (l-cos ~)
wherein D is the width of the hex wrench, as defined by the
distance between opposing sides.
In the preferred embodiment, ~ is equal to 360
2(6)
ox ~ 30. Thus~ the distance from Fl to the nearest inter-
20 cept along the major axis is e~ual to 1~2 D cos 30 or 0.433D.
Like~ise~ the distance from midpoint 28 to either Fl or F2 is 0.067D.
The head portion 18 is shown as terminating in a flat
surface 32, The flat surface 32 can be seen to have the same
sh~pe as the cxoss section of the shank portion 14, or as a
hexagon, as in the preferred e~nbodiment. The flat surface 32 has
a width preferably as a function of khe width of the shank portion.
The width is, of course, dependent upon the si~e of the cap screw
with which the wrench is to be used. It is to be understood that
while we show a flat end surface 32, the surface can be rounded or
take any other suitable form.
Between the end surface 32 and elliptical surface 22
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z~
there may be an inclined surface 34 to provide a smooth transitionbetween elliptical surface 22 and flat end surface 32. The inclin-
ed surface 34, whexe provided, is preferably some function of -the
diameter of the hex wrench. The starting point of the inclined sur-
face is de~ermined by the angle ~ which may be a 60~ angle formedwith the major ax.is at either foci, Fl or F2.
The neck portion 16 is a portion formed between the
head portion 18 and the shank portion 14. As shown, the neck
portion substantially conforms to a portion of a hyperboloid of
revolution whose axis of revolution is the central axis 27 of the
hex wrench. The neck portion may be the form of an inwardly
curved surface 36 of revolution, however. Where it is feasible
to make the head of a larger cross-sectional width than the
shank, the neck may simply curve inwardly from the head to the
shank. The neck begins at an area of confluence 42 and at that
area is tangential to the elliptical surface of the head portion 18.
The area of confluence 42 is spaced from the intercept 29
by an angle ~ which depends upon the amount of tilting desired.
This angle ~ may vary from 10 to 50~ depending upon the extent
to which the neck is recessed to obtain more tilting. Obviously,
the greater the angle ~ is, the smaller will be the neck and
the more tilting will be possible. Where it is desired -to have
a thicker neck for purposes of strength and where a large amount -
of tilting is not necessary, the angle ~ will be relatively small.
It has been found that by making the surface of the
head elliptical with the elements of theellipse related, as
described above, to the numbers o~ sides o~ the tool, it is 7
possible to obtain a much greater tilting without bending of
the wrench as it is used than has previously been possible.
In actual practice, curved surfaces 22 need not be strictly
elliptical. They can be arcs of a circle with a center of
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curvature at the point Fl, rather than along the center line
28 as would normally be the case. As has been explained above,
the distance between the point Fl and the midpoint 28 is de-
pendent upon the number of sides. If one had an infinite
number of sides, this distance would be zero and the surfaces
22 would be arcuate surfaces with the centers of curvature
at the midpoint 28. The fewer the number of sides, the greater
will be the displacement of the center of curvature of the
suxface 22 from the midpoint 28. By providing a surface of this
type, closely approaching a portion of an elliptical surface,
it is possible, as explained above, to get a very substantial
degree of tilting of the tool as the tool is turned without
binding between the head of the tool and the socket of the
screw with which the tool is being used.
While we have shown a specific embodiment of the
invention for purposes of illustxation, it is to be understood
that the invention is limited solely by the scope of the
appended claims.
