Note: Descriptions are shown in the official language in which they were submitted.
~043~
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to set screws and,
more particularly, to set screws of the "cup-point" type.
2. Description of the Prior Art
Set screws are used in various applications to
removeably secure fly wheels, pinions, pulleys, cams, propellers
and the like to shafts. In such applications, the set screws
experience both vibrations and shock loads which might tend to
loosen them.
Many set screw points have been designed in the past to
increase the ability of the set screw to resist vibration.
Examples of such set screws include: U.S. Patent No. 1,330,792,
2OL~ 4
Frick; U.S. Patent No. 2,235,435, Koester: U.S. Patent No.
2,245,525, Dicely; U.S. Patent No. 2,462,gl0, Simmons; U.S.
Patent No. 2,778,265, Brown; U.S. Patent No. 2,295,314, Whitney;
U.S. Patent No. 2,907,245, Whitson; U.S. Patent No. 3,286,754,
Klooz et al.; U.S. Patent No. 3,419,058, Walker; and U.S. Patent
No. 3,920,060, Heldmann et al.
Of particular interest is U.S. Patent No. 2,314,274,
Hallowell, which discloses certain types of set screws having
knurls on the work-engaging end wherein the work-engaging
extremity is provided with centering means that will be effective
to establish the position of the screw with the work prior to
engagement of the interlocking means. Also, U.S. Patent No.
2,992,669, Fesmire, discloses a certain knurled cup-point set
screw wherein the cup is counter-bored. Additionally, U.S.
Patent No. 4,764,068, Crispell, discloses a set screw having a
threaded shank and a cup-point formed at one end of the shank
wherein the cup-point has an outer frustoconical surface and an
inner cylindrical surface which together define an annular wedge
terminating in a circular edge. A portion of the outer frusto-
conical surface remote from the circular edge is provided with
knurling.
Most of the above-mentioned prior art set screws have
cup-point configurations formed by a machining process. However,
none of these prior art references suggest the novel work-
engaging end portion of the set screw of the present invention
which can be formed by a forging process.
SUMMARY OF THE Ihv~ ON
This invention relates to a set screw comprising a
shank having external threads and a work-engaging end portion
integrally formed at one end of the shank. The work-engaging end
9 ~ ~
portion has a frustohemispherical outer surface comprising a
plurality of circumferentially spaced serrations in the form of
teeth. Each of the teeth comprises a ramp extending outwardly
from a root to a crest thereof with the ramp being inclined in a
direction which is opposite to the direction of rotation of
engaging the set screw in a workpiece. A cavity is formed in the
outer extremity of the work-engaging end portion. The cavity
cooperates with the frustohemispherical outer surface to form
therebetween an annular wedge.
The cavity can be generally conical or generally
polyhedral in shape, having its largest diameter equal tc and
coterminous with the outermost periphery of the frusto-
hemispherical outer surface. Additionally, the cavity can be
defined by a first portion immediately interior to the outermost
portion of the work-engaging end portion and comprising a
generally cylindrical wall concentric with the longitudinal axis
of the shank. The cavity can be also further defined by a second
portion interior to the cylindrical first portion with the second
portion being concentric with the longitudinal axis of the shank
and being generally conical in shape, having its largest diameter
equal to and coterminous with the innermost periphery of the
cylindrical first portion. Moreover, the cavity formed in the
work-engaging end portion can extend inwardly to a point in the
shank beyond the work-engaging end portion.
The depth of each serration decreases towards the
outermost periphery of the frustohemispherical outer surface.
Advantageously, the teeth are curv~d and equally spaced about the
frustohemispherical outer surface. The teeth of the present
invention facilitate imbedding of the set screv in the workpiece
when the set screw is rotated to engage the workpiece and the
teeth further deter loosening of the set screw after engagement
with the workpiece.
~ 0 ~ 4
The rounded work-engaging end portion or "cup-point"
configuration of the present invention allows its cup-point to be
shorter than a straight knurl cup-point having the same cup and
point diameters. Therefore, the threads on the shank are closer
to the cup-point, which is particularly advantageous when the set
screw's length is less than its diameter. Furthermore, the
serrations are stronger at the outer edge of the cup-point where
stress is high than it is on the side because the serration depth
increases away from the edge. This allows the serrations to
engage more of the mating surface of the workpiece when the
serrations penetrate deep into the surface. The edge remains
more durable because the serration depth is smaller at the cup-
point edge. Additionally, the unique work-engaging end portion
of the present invention can be readily and efficiently formed by
a forging process.
Accordingly, it is an object of the present invention
to provide a set screw having a novel work-engaging end portion
configuration. It is a further object of the present invention
to provide a work-engaging end portion which can be readily and
efficiently formed on the shank by a forging process. It is also
an object of the present invention to provide a novel set screw
having more of the shank's threads near the outer edge. It is an
additional object of the present invention to provide a work-
engaging end portion configuration which is stronger at the outer
edge where stress is higher.
These and many other objects, features and advantages
of the present invention will become apparent to those skilled in
the art when the following description of the preferred
embodiments is read in conjunction with the drawings appended
hereto.
6 4
BRIEF ~ESCRIPTION OF THE DRAWINGS
In the drawings, where like refere~nce nu~erals refer to
like elements throughout:
FIG. 1 is a side elevational view of the point or work-
engaging end portion of the set screw in accordance with thepresent invention;
FIG. 2 is a top plan view of the set screw in
accordance with the present invention;
FIG. 3 is a partly cutaway side elevational view of the
point or work-engaging end portion of the set screw in accordance
with the present invention;
FIG. 4 is an exaggerated schematic cross sectional view
taken along 4-4 of FIG. 2 illustrating a tooth in accordance with
the present invention; and
~IG. 5 is an exaggerated schematic view taken along 5-
5 of FIG. 3 illustrating the tooth profile of the serrations
formed on the set screw in accordance ~ith the present lnvention.
2 0 ~
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, ~IGS. 1 throuqh 3
illustrate a set screw lO adapted to engage a workpiece in
accordance with the present invention. The set screw 10 is
comprised of a shank 11 having a longitudinal axis 12 and
external threads 13 along a substantial portion of the shank's
length. The threads 13 define a direction of rotation of
engaging the set screw lO in the workpiece. In use, the set
screw 10 is in threaded engagement with a member and is tightened
in the member against a workpiece, such as a shaft or rod. The
directional arrow 14 in FIGS. 2 and 3 shows the direction of
rotation of engaging the set screw 10 as defined by the threads
13 for the embodiment of the present invention illustrated
therein. In FIGS. 2 and 3, the direction of rotation is in a
counterclockwise direction. However, the direction of rotation
may also be in a clockwise direction as can be appreciated by
those skilled in the art.
A cup-point or work-engaging end portion 15 is
integrally formed at one end of the shank 11. A wrench receiving
socket (not shown) of any desired configuration can be formed at
the other end of the shank 11 for receiving a suitable screw
rotating wrench so that the set screw 10 can be rotated for
tightening against the workpiece. The work-engaging end portion
15 has a frustohemispherical outer surface 16. The term
"frustohemispherical" as used herein means a half sphere-type
2~3~
configuration in which the top portion is cut off by a plane
generally parallel to the base. In a preferred em~odiment, the -
intersection of the outer surface 16 of the work-engaging end
portion 15 and the shank 11 defines the end portion's base or a
first plane 17 generally normal to the shank's longitudinal axis
12. Also, the frustohemispherical outer surface 16 is comprised
of a plurality of circumferentially spaced serrations in the form
of teeth 18. The serrations are radially disposed on the outer
surface 16 in relation to the shank'~ longitudinal axis 12. The
teeth 18 are curved and, advantageously, the teeth 18 are equally
spaced about the outer surface 16. For example, the teeth 18
will be separated by an angle 39 of 20~ if the screw 10 has a
total of eighteen teeth, as illustrated in FIG. 2. However, the
total number of teeth is not critical and may vary depending on
the size and application of the screw, as can be appreciated by
those skilled in the art.
Each of the teeth 18 is comprised of a root 19, a crest
20, and a ramp 21 extending outwardly in relation to the
longitudinal axis 12 from the root l9 to the crest 20 thereof.
Furthermore, the ramp 21 is inclined outwardly in a direction
which is opposite to the direction of rotation of engaging the
set screw 10 in the workpiece. For example, if the direction of
rotation of engaging the set screw lO in the workpiece is in a
counterclockwise direction, then the ramp 21 is inclined
outwardly in a clockwise direction, as illustrated in FIGS. 2 and
3. However, if the direction of rotation of engaging the set
2 ~
screw 10 in the workpiece is in a clockwise direction, then the
ramp 21 is inclined outwardly in a counterclockwise direction.
The orientation of the teeth 18 in relation to the direction of
rotation of engaging the set screw 10 facilitstes imbedding of
the set screw 10 in the workpiece when the set screw 10 is
rotated to engage the workpiece and also deters loosening of the
set screw 10 after engagement with the workpiece.
A cavity 22 is formed in the outer extremity of the
work-engaging end portion 15. The cavity 22 generally extends
inwardly towards the first plane 17 and to the longitudinal axis
12 of the shank 11. The cavity 22 can also extend inwardly to a
point in the shank 11 along the longitudinal axis 12 beyond the
first plane 17. The cavity 22 cooperates with the frusto-
hemispherical outer surface 16 to form therebetween an annular
wedge 23, which is generally concentric with the shank's
longitudinal axis 12 and terminates with the outermost periphery
of the outer surface 16 in an edge 24. In a preferred
embodiment, the edge 24 defines a second plane 25 generally
normal to the shank's longitudinal axis 12. The ~dge 24 can be
sharp or rounded. Preferably, the edge 24 is rounded. Also, the
length 30 of the ramp 21 extending outwardly from the root 19 to
the crest 20 of each tooth 18 decreases from the first plane 17
to the second plane 25.
The work-engaging end portion 15 presents the edge 24
of the wedge 23 to the surface of the workpiece to cause it to
2 ~
displace the surface material of the workpiece when the set screw
10 is used. As can be appreciated by those skilled in the art,
the end portion 15 is designed to bite into the workpiece's
surface material when the set screw 10 is tightened. Upon
S further tightening, the teeth 18 engage the ~orkpiece. The
cavity 22 limits the penetration of the teeth 18 into the
workpiece's surface. As noted above, the orientation of the end
portion's teeth 18 resists the loosening effects of vibration,
and anchors the set screw 10 to the workpiece.
The cavity 22 can have various configurations. For
example, the cavity 22 can be conical in shape, having its
largest diameter 26 equal to and coterminous with the outermost
periphery of the frustohemispherical outer surface 16. The
included angle 27 of the conical cavity can be from about 90~ to
about 130~ and, preferably, the included angle 27 is 90~.
Another cavity configuration that can be utilized in accordance
with the present invention, is a cavity 22 that is generally
polyhedral in shape, having its largest diameter 26 equal to and
coterminous with the outermost periphery of the frustohemispherical
outer surface 16.
Advantageously, the cavity 22 can be of the type
illustrated in FIG. 3 in which the cavity 22 is defined by a
first portion 28 immediately interior to the outermost portion of
the work-engaging end portion 15. This first portion 2~ is
comprised of a cylindrical wall concentric with the shank's
2048~64
longitudinal axis 12. This type of cavity 22 can be
further defined by a second portion 29 interior to the
cylindrical first portion 28. The second portion 29 is
concentric with the shank's longitudinal axis 12 and it
is generally conical in shape, having its largest
diameter 26 equal to and coterminous with the innermost
periphery of the cylindrical first portion 28. The
above-mentioned cavity configurations are described in
U.S. Patent No. 4,764,068, Crispell.
Details of the teeth in a preferred embodiment
of the present invention are illustrated in FIGS. 4 and
5. Common points of reference A', B', C' and D' for a
tooth in FIGS. 2 through 5 assist in understanding the
tooth's dimensional details. FIG. 4 shows an
exaggerated schematic cross sectional view taken along
4-4 of FIG. 2. A first radius 31 defines the crest 20
of the tooth, and the first radius 31 terminates at the
first plane 17 normal to the shank's longitudinal axis
12. A second radius 32 defines the root 19 of the
adjoining tooth, and the second radius 32 terminates at
another plane 33 normal to the shank's longitudinal
axis 12 and parallel to the first plane 17. The
difference between the first radius 31 and the second
radius 32 is shown as the distance 36 in FIGS 4 and 5.
The radii would meet at point 34 on the shank's
longitudinal axis 12 if the first radius 31 and the
second radius 32 were extended to the longitudinal axis
12, as illustrated in FIG. 4. FIG. 4 also illustrates
that the depth 35 of each tooth or serration
--10--
, .
~ 2~3~lt~
decreases towards the edge 24 or outermost periphery of the
frustohemispherical outer surface.
FIG. 5 shows an exaggerated schematic view of the tooth
profile taken along 5-5 of FIG. 3. In FIG. 5, the root B', ramp
21, and crest C' of a tooth are shown, along with the crest A'
and root D' of adjoining teeth. The angle 37 between the ramp 21
of the tooth and a line intersecting the crest C' of the tooth
and the crest A' of the adjoining tooth in the first plane 17 can
be about 6~ to about 15~ and, preferably, the angle is 15~.
Furthermore, the internal angle 38 between the crest C' wall and
the ramp 21 is approximately 9O~.
Advantageously, the work-engaging end portion of the
present invention can be formed by a forging process at low
pressure. Since the normal high production forging methods known
in the art require that such a work-engaging end portion be
impressed on the screw blank by tooling in the bed of the forging
machine, a work-engaging end portion had to be develop~ed at
minimum pressure since friction on the wall of the die absorbs
some of the forging force as the screw's length increases.
Therefore, the available pressure at the point of the blank is
dependent on product length. A work-engaging end portion
configuration that can be forged at low pressure allows a greater
range of lengths to be forged. The configuration of the present
invention utilizes an extrusion die design concept for the
external shape. In order to reduce pressure further, the preform
20~8~
utilized, which is subsequently extruded, has a cavity to
facilitate the inward collapse during extrusion.
Furthermore, the forged edge of the work-engaging end
portion can be rounded, which has the potential for performing
better than a machined sharp edge because the outer surface is
work hardened instead of cut. Moreover, the serrations of the
present invention are stronger at the edge where stress is high
than on the side of the outer surface because the serration depth
increases away from the edge. This allows the serrations to
engage more of the mating surface of the workpiece when the
serrations penetrate deep into the mating surface. The edge also
remains more durable because the serration depth is small at the
cavity edge. The serration penetration further works in
conjunction with the cavity design. The cavity limits the
penetration of the serrations into the mating surface.
Additionally, the rounded work-engaging end portion or cup-point
configuration of the present invention allows its cup-point to be
shorter than the straight knurl cup-point known in the prior art.
Therefore, more threads on the shank are closer to the cup-point
when compared to a straight knurl cup-point having the same cup
diameter and point diameter. This is an advantage when the set
screw's length is less than its diameter since more collar thread
engagement prevents the screw from stripping the collar's threads
in such an application.
2~ 4
While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous
other forms and modifications of this invention will be obvious
to those skilled in the art. The appended claims and this
invention generally should be construed to cover all such obvious
forms and modifications which are within the true spirit and
scope of the present invention.
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