U.S. patent number 3,794,092 [Application Number 05/198,146] was granted by the patent office on 1974-02-26 for locking fastener.
This patent grant is currently assigned to Textron Inc.. Invention is credited to Raymond H. Carlson, Bernard F. Reiland.
United States Patent |
3,794,092 |
Carlson , et al. |
February 26, 1974 |
LOCKING FASTENER
Abstract
A locking screw arrangement and fastener member are disclosed
which provide for predictability and control of the locking action
attained. In addition, there is disclosed a novel type of locking
thread configuration wherein the leading or following flank of one
or more thread turns on the fastener are bulged outwardly in an
axial direction, with the opposite flank depressed, whereby said
bulged flank will engage the corresponding flank of the female
member to produce flank-to-flank interference. In order to obtain
said predictability and control, said locking arrangement employs
an internally threaded female member having a thread configuration
formed within industry accepted tolerances, which female member is
engaged with an externally threaded fastener having a construction
which eliminates any variables due to the tolerance encountered in
the thread form of the female member that adversely effect the
locking action. In this regard, the threaded portion of the
fastener includes a preparation section and a locking section, the
thread turns and the preparation section being such as to reshape
and size the internal thread of the female member upon engagement
therewith, thereby eliminating the effect of dimensional variables
that may be encountered. Therefore, upon subsequent engagement of
said reshaped internal threads with the thread turns of the locking
portion, a predetermined locking action will be obtained.
Inventors: |
Carlson; Raymond H. (Rockford,
IL), Reiland; Bernard F. (Rockford, IL) |
Assignee: |
Textron Inc. (Providence,
RI)
|
Family
ID: |
26784276 |
Appl.
No.: |
05/198,146 |
Filed: |
November 12, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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91730 |
Nov 23, 1970 |
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Current U.S.
Class: |
411/310; 411/938;
470/185 |
Current CPC
Class: |
F16B
39/30 (20130101); B21H 3/025 (20130101); Y10S
411/938 (20130101) |
Current International
Class: |
B21H
3/00 (20060101); B21H 3/02 (20060101); F16B
39/30 (20060101); F16B 39/00 (20060101); F16b
039/30 () |
Field of
Search: |
;151/22,21B ;85/46 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Parsons, Jr.; Marion
Attorney, Agent or Firm: Olson, Trexler, Walters &
Bushnell
Parent Case Text
REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of applicant's U. S.
application Ser. No. 91,730, filed Nov. 23, 1970 and now abandoned.
Claims
We claim:
1. An externally threaded male locking fastener for engagement with
an internally threaded female member, said female member having an
internal thread which is of a substantially circular cross-section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of thread
turns of the radially relieved type, said plurality of thread turns
having one flank thereof bulging outwardly at a first axial
direction with the opposite flank of said thread turns depressed
inwardly in said first axial direction, whereby upon engagement of
said preparation portion, with the internal thread of a female
member regardless of the industry tolerances employed, said
internal threads will be reshaped and provided with uniform
corresponding bulging and depressed flanks, deflected axially with
regard to their initial configuration; and a locking thread portion
positioned further from said work-entering end of the screw than
said preparation portion, said locking portion including a
plurality of thread turns having a thread form which will upon
engagement with said uniformly reshaped axially deflected bulging
internal threads, produce a prescribed degree of interference along
one or more of the engaged thread flanks, to lock said male and
female members in assembled relation.
2. An externally threaded male locking fastener as defined in claim
1 wherein said locking thread portion includes a plurality of
thread turns having relatively straight flank surfaces, disposed to
engage said bulging flanks formed on said internal thread by the
preparation portion, said engagement producing the desired flank
interference.
3. An externally threaded male locking fastener as defined in claim
1, wherein said locking thread portion includes a plurality of
locking thread turns having one flank thereof bulging outwardly in
a second axial direction opposite to said first direction, with the
oppositely disposed flank of said locking thread turn being
depressed, such that upon engagement of said locking thread turn
with said previously reshaped internal thread, flank-to-flank
contact will be obtained between the opposed engaged bulging flanks
of said internal thread and said locking thread, respectively,
producing the desired flank interference.
4. A locking screw according to claim 1 further provided with a
transition thread section located between and joining said
preparation thread portion and said locking thread portion and
having an intermediate thread flank configuration.
5. A locking screw according to claim 4 wherein said transition
thread section is characterized by a substantially straight flank
cross section.
6. A locking screw according to claim 1 wherein said bulging flank
is convexly rounded and wherein said relieved flank is concavely
rounded.
7. A locking screw according to claim 1 wherein said bulging flank
extends angularly outwardly to an apex proximate the pitch cylinder
of said screw while said relieved flank extends angularly inwardly
to an apex also proximate the pitch cylinder of said screw.
8. An externally threaded locking fastener member adapted to be
engaged with an internally threaded female member, having an
internal thread formation which is of a substantially circular
cross section and of generally uniform dimensions held within
accepted, industry specified tolerances, said fastener member
including a driving head, a shank portion and a tapered
work-entering end, with an external thread formed on at least a
portion of said shank, said external thread including, a
preparation portion disposed adjacent said tapered work-entering
end and including a plurality of sizing thread turns of the
radially relieved type and having a standard profile, said sizing
thread turns having an effective pitch diameter which is at least
as great as the maximum allowable pitch diameter of the internal
thread of the female member to be engaged therewith, such that upon
engagement, the sizing thread turns will reshape said internal
thread to a prescribed configuration having a pitch diameter
determined by said sizing thread turns, regardless of the internal
thread tolerances encountered; and a locking thread portion
positioned further from said work-entering end of the screw than
said preparation portion, and said locking portion including at
least one full thread turn, one flank of which bulges axially
outward with the opposite flank being depressed, whereby upon
engagement with said reshaped internal thread flank interference
will be obtained along said bulging thread flank to lock the
respective male and female members in assembled relation.
9. An externally threaded male locking fastener for engagement with
an internally threaded female member, said female member having an
internal thread which is of a substantially circular cross section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of thread
turns of the radially relieved type, said thread turns having an
effective pitch diameter that is at least as great as the maximum
allowable pitch diameter of said internal thread permitted by said
industry tolerances, such that upon engagement of the preparation
portion with an internally threaded member, regardless of the
tolerances encountered, said internal thread will be reshaped and
sized to a desired, predicted uniform configuration having a pitch
diameter determined by said preparation portion; and a locking
thread portion positioned further from said work-entering end of
the screw than said preparation portion, said locking thread
portion includes a plurality of thread turns having a pitch
diameter greater than the effective pitch diameter of the thread
turns on said preparation portion, such that said locking thread
portion will, upon engagement with said internal thread after
reshaping thereof by said preparation portion, produce a prescribed
degree of interference along one or more of the engaged thread
flanks, to lock said male and female members in assembled
relation.
10. An externally threaded male locking fastener for engagement
with an internally threaded female member, said female member
having an internal thread which is of a substantially circular
cross section and of generally uniform dimensions held within
accepted, industry specified tolerances, said male member including
a driving head, a shank portion, and a tapered work-entering end,
with an external thread formation on at least a section of said
shank, said external thread formation including, a preparation
portion disposed adjacent said tapered work-entering end and
including a plurality of thread turns of the radially relieved type
said thread turns having an effective pitch diameter that is at
least as great as the maximum allowable pitch diameter of said
internal thread permitted by said industry tolerances, such that
upon engagement of the preparation portion with an internally
threaded member, regardless of the tolerances encountered, said
internal thread will be reshaped and sized to a desired, predicted
uniform configuration having a pitch diameter determined by said
preparation portion; and a locking thread portion positioned
further from said work-entering end of the screw than said
preparation portion, said locking thread portion including a
plurality of thread turns having one flank thereof bulging axially
in a first direction with the opposite flank of each said turn
depressed inwardly in the same direction, such that said locking
thread will, upon engagement with said internal thread after
reshaping thereof by said preparation portion, produce a prescribed
degree of interference along one or more of the engaged thread
flanks, to lock said male and female members in assembled
relation.
11. In combination, an externally threaded male member and an
internally threaded female member, said female member having an
internal thread which is of a substantially circular cross section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of sizing
thread turns of the radially relieved type, said sizing thread
turns having an effective pitch diameter that is at least as great
as the maximum allowable pitch diameter of said internal thread,
such that upon engagement, said sizing thread turns will reshape
and size said internal thread, eliminating all variances due to
tolerances and producing a thread form of predicted uniform
configuration and pitch diameter, regardless of the internal thread
tolerances encountered; and a locking thread portion positioned
further from said work-entering end of the screw than said
preparation portion, said locking portion including at least one
thread turn having a pitch diameter greater than the effective
pitch diameter of said sizing thread turns, by a preselected valve,
such that upon engagement of said reshaped internal thread with
said locking thread turns, a predicted flank-to-flank interference
will be obtained, which interference will maintain said male and
female members in assembled relation.
12. In combination, an externally threaded male member and an
internally threaded female member, said female member having an
internal thread which is of a substantially circular cross section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of sizing
thread turns of the radially relieved type, said sizing thread
turns having an effective pitch diameter that is at least as great
as the maximum allowable pitch diameter of said internal thread,
such that upon engagement, said sizing thread turns will reshape
and size said internal thread, eliminating all variances due to
tolerances and producing a thread form of predicted uniform
configuration and pitch diameter, regardless of the internal thread
tolerances encountered; and a locking thread portion positioned
further from said work-entering end of the screw than said
preparation portion, said locking portion including at least one
full thread turn, one flank of which bulges axially outward with
the opposite flank being depressed, whereby upon engagement with
said reshaped internal thread flank, a prescribed degree of
interference will be obtained along said bulging thread flank to
lock the respective male and female members in assembled
relation.
13. In combination, an externally threaded male member and an
internally threaded female member, said female member having an
internal thread which is of a substantially circular cross section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of thread
turns of the radially relieved type, said thread turns having one
flank thereof bulging outwardly in a first axial direction with the
opposite flank of said thread turns depressed inwardly in said
first axial direction, whereby upon engagement of said preparation
portion, with the internal thread of said female member, said
internal thread will be reshaped to a desired, predicted
configuration and provided with corresponding bulging and depressed
flanks, deflected axially with regard to their initial
configuration; and a locking thread portion position further from
said work-entering end of the screw than said preparation portion,
said locking portion including at least one locking thread turn
having one flank thereof positioned to engage said reshaped,
axially deflected bulging flank of said internal thread in
interferring relation to produce a locking action.
14. In combination, an externally threaded male member and an
internally threaded female member, said female member having an
internal thread which is of a substantially circular cross section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of thread
turns of the radially relieved type, said thread turns having one
flank thereof bulging outwardly in a first axial direction with the
opposite flank of said thread turns depressed inwardly in said
first axial direction, whereby upon engagement of said preparation
portion, with the internal thread of said female member, said
internal thread will be reshaped to a desired, predicted
configuration and provided with corresponding bulging and depressed
flanks, deflected axially with regard to their initial
configuration; and a locking thread portion positioned further from
said work-entering end of the screw than said preparation portion,
said locking portion including at least one locking thread turn
having one flank thereof bulging outwardly in a second axial
direction opposite to said first direction, with the oppositely
disposed flank of said locking thread in turn being depressed, such
that upon engagement of said locking thread turn with said
previously reshaped internal thread flank-to-flank contact will be
obtained between the bulging flank of said locking thread and that
of said internal thread, respectively, producing flank-to-flank
interference which maintains said male and female members in
assembled relation.
15. In combination, an externally threaded male member and an
internally threaded female member, said female member having an
internal thread which is of a substantially circular cross section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of thread
turns of the radially relieved type, said preparation portion
including a plurality of sizing thread turns having a generally
standard profile and an effective pitch diameter at least as great
as the maximum allowable pitch diameter of said internal threads,
with engagement of said sizing thread turns with said internal
threads reshaping said internal threads to a predetermined uniform
configuration having a prescribed pitch diameter, regardless of the
internal thread tolerances encountered; and a locking thread
portion positioned further from said work-entering end of the screw
than said preparation portion, and having a thread form which will,
upon engagement with said uniformly reshaped internal threads,
produce a prescribed degree of interference along one or more of
the engaged thread flanks, to lock said male and female members in
assembled relation.
16. In combination, an externally threaded male member and an
internally threaded female member, said female member having an
internal thread which is of a substantially circular cross section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of thread
turns of the radially relieved type, said thread turns having an
effective pitch diameter that is at least as great as the maximum
allowable pitch diameter of said internal thread permitted by said
industry tolerances, such that upon engagement of the preparation
portion with said internal thread, regardless of the tolerance
encountered, said internal thread will be reshaped and sized to a
desired, predicted uniform configuration, having a shape and pitch
diameter determined by said preparation portion; and a locking
thread portion positioned further from said work-entering end of
the screw than said preparation portion, and having a thread form
which will, upon engagement with said internal thread after
reshaping thereof by said preparation portion, produce a prescribed
degree of interference along one or more of the engaged thread
flanks, to lock said male and female members in assembled
relation.
17. A combination as defined in claim 16, wherein said locking
thread portion includes a plurality of thread turns having a pitch
diameter greater than that of the thread turns on said preparation
portion.
18. A combination as defined in claim 16, wherein said locking
thread portion includes a plurality of thread turns having one
flank thereof bulging axially in a first direction with the
opposite flank of each said turn depressed inwardly in the same
direction, such that upon engagement with said reshaped internal
thread, said flank interference will be obtained along said bulging
flanks.
19. In combination, an externally threaded male member and an
internally threaded female member, said female member having an
internal thread which is of a substantially circular cross-section
and of generally uniform dimensions held within accepted, industry
specified tolerances, said male member including a driving head, a
shank portion, and a tapered work-entering end, with an external
thread formation on at least a section of said shank, said external
thread formation including, a preparation portion disposed adjacent
said tapered work-entering end and including a plurality of thread
turns of the raidally relieved type, said plurality of thread turns
having one flank thereof bulging outwardly in a first axial
direction with the opposite flank of said thread turns depressed
inwardly in said first axial direction, such that upon engagement
of said preparation portion with the internal thread of said female
member, regardless of the industry tolerances employed, said
internal threads will be reshaped and provided with a uniform
thread form determined by said preparation portion, said uniform
thread form having corresponding bulging and depressed flanks,
deflected axially with regard to their initial configuration; and a
locking thread portion positioned further from said work-entering
end of the screw then said preparation portion, said locking
portion including a plurality of thread turns having a thread form
which will, upon engagement with said uniformly reshaped axially
deflected bulging internal threads, produce a prescribed degree of
interference along one or more of the engaged thread flanks, to
lock said male and female members in assembled relation.
20. A combination as defined in claim 19 wherein said locking
thread portion includes a plurality of thread turns having
relatively straight flank surfaces, disposed to engage said bulging
flanks formed on said internal thread by the preparation portion,
said engagement producing the desired flank interference.
21. The combination as defined in claim 19 wherein said locking
portion includes a plurality of locking thread turns having one
flank thereof bulging outwardly in a second axial direction
opposite to said first direction, with the oppositely disposed
flank of said locking thread turn being depressed, such that upon
engagement of said locking thread turn with said previously
reshaped internal thread, flank-to-flank contact will be obtained
between the opposed engaged bulging flanks of said internal thread
and said locking thread, respectively, producing the desired flank
interference.
Description
BACKGROUND OF THE INVENTION
Threaded fastener devices manufactured within usual commercial
tolerances are usuallly characterized by at least a slight
clearance between mating parts, unfortunately permitting them to
shake loose under vibration unless an auxiliary device such as a
lock-nut or a lock-washer is also employed. Even in the case when a
relatively tight fit is specified between mating parts, the holding
ability of the threads is usually unsatisfactory because of
imperfection in the thread form in one or the other, or both,
parts. Substantial contact will be attained between a few points of
adjacent thread flanks when a screw is drawn up against a nut or
workpiece, with other flank portions being held apart by the
already engaged thread points.
Therefore, with a view toward elimination of auxiliary devices,
various lock screws have been devised for producing a firm but
limited contact between the threads of mating fastener devices.
Typically, such lock screws are arranged to provide interference
contact between certain portions of the locking screw and mating
portions of the female thread. However, locking screw constructions
as have been devised heretofore have had the disadvantage of
tending to gall, break or freeze portions of the mating threads. As
such, these prior constructions either produce relatively
ineffective locking, or if sufficient interference is provided so
that locking is assured, then galling or other damage occurs
leading to breakage or permanent freezing of the parts
together.
Another factor that has contributed to the unacceptable nature of
prior art locking arrangement is their inability to accommodate the
relatively wide industry accepted tolerances encountered with
regard to mating threaded parts, and still provide effective
predictable locking or holding action. In this regard, most forms
or types of prior art locking screws employ a measure of
interference between the male and female threads. However, since
both the male and female thread configurations will vary within
relatively wide tolerances, any attempt at predicting the degree of
locking action is religated to an educated guess, there being no
certainty in the control of this factor.
With present day mass production methods, not only is it more
difficult to form an internal thread than an external thread, but
it is also significantly harder to maintain close dimensional
tolerances with an internal thread. While all of the various thread
dimensions may be important when attempting to control the locking
action, depending of course, on the type of locking engagement to
be effected, it is believed that a specific example will clarify
this point.
Where flank-to-flank interference in one or both thread flanks is
to be obtained, the pitch diameters of the respective mating
threads can be a critical factor. In the screw thread art, the
"pitch diameter" is defined as the diameter of an imaginary
cylinder, the surface of which would pass through the thread
profiles at such points as to make the width of the thread and that
of the groove equal. For example, with a conventional 5/16 inch nut
and screw assembly, the industry standards will accept a pitch
diameter for the nut that varies between 0.2764 and 0.2817 inches,
a tolerance of 0.0053 inches. The industry accepted tolerances for
the pitch diameter of the corresponding male screw member is 0.004
inches, the pitch diameter being between 0.2712 and 0.2752 inches.
It must be emphasized that these dimensional tolerances are
employed where no locking action is envisioned, and a clearance is
to be maintained. In order to obtain a locking action of the
flank-to-flank type with the nut and thread of the preceeding
example, the form or configuration of one or more of the thread
turns on the male threaded member must be varied in some manner so
as to bring the respective thread flanks into interfering
engagement. However, the degree of flank interference that will be
obtained will vary considerably, depending on whether the
dimensions of the thread form on the nut are at the upper or lower
end of the tolerance range.
Whether flank-to-flank interference is employed, or some other
known type of thread interference is utilized, to be commercially
acceptable, a locking arrangement must produce thread interference
which falls within certain limits, depending of course on the
intended use. If the interference is only slight, the locking
action obtained may be insufficient for the user's purpose, and the
threaded engagement may be loosened under vibration or prolonged
use. On the other hand, if interference is excessive, galling of
the threads may ensue and also, extremely high driving torques will
be required to engage the mating elements properly. Therefore, it
is extremely desirable that some measure of predictability and
control of the degree interference be provided, and that this be
obtained by present day mass production methods, without resort to
precision machining or forming.
Unfortunately however, with conventional internally threaded
members, the relatively wide tolerances encountered introduces a
variable that will effect the degree of locking interference which
preclude the obtaining of adequate predictability and control of
the locking action. Accordingly, the present invention overcomes
this problem, inherent in prior art locking arrangements by
providing an externally threaded fastener which can effectively
eliminate any variables due to the internal thread tolerances, and
thus predictability and control of the locking action is
obtained.
More specifically, the present invention provides an internally
threaded fastener for use in a locking assembly wherein the
threaded segment of said fastener includes a preparation portion,
and a locking portion. The preparation portion includes a thread
form preferably of the radially relieved type which is capable of
reshaping the threads of the female member to a desired, predicted
configuration. The thread turns on the locking portion are designed
and configurated to provide a desired type and degree of
flank-to-flank interference when engaged with the internal threads
of the female member subsequent to reshaping thereof by the
preparation portion. As such, when the locking thread turns engage
the reshaped internal threads, the interference, and
correspondingly, the locking action obtained, is predictable and
controllable. Therefore, the variances in the nut thread dimensions
due to the industry tolerances no longer are factors which bear
significantly on said locking action obtained.
The hereinafter disclosed embodiments of the present invention
envision the elimination of the variables occasioned by the thread
tolerances in several manners, as will be explained more completely
with reference to the drawings. One form of the invention employs a
preparation portion having a plurality of sizing thread turns of a
general standard form or configuration. That is, the thread turns
have relatively flat or straight flank profiles, which define the
included angle of the thread form. These thread turns are of the
radially relieved type designed to engage and cold work the
internal thread of the female member, thereby reshaping the thread
form of said member to a configuration determined by the relative
form and dimensions of the sizing threads. In this regard, the
sizing thread turns are provided with an effective pitch diameter
that is at least as great, or greater than the maximum allowable
pitch diameter that will be encountered with corresponding female
members having an internal thread formed to the industry accepted
tolerances. Therefore, no matter what the variance in the pitch
diameter of the thread on the female member, it is assured that
upon initial engagement said thread will be cold worked and
reshaped to a desired configuration which, when engaged with the
locking section, will give a predicted type and degree of locking
action.
Another embodiment of the present invention envisions employment of
a preparation portion wherein the relative dimensional differences
between the sizing thread and the internal thread are of little or
no significance. In this regard, the sizing threads on the
preparation portion of the male fastener are provided with a
specific configuration designed to deform or deflect the internal
threads of the female member in a first axial direction. As such,
the resulting thread form which is presented to the locking portion
of the male fastener will have the flank displaced axially, which
displacement will produce flank-to-flank interference. Since the
final relative flank displacement which produces locking is, in
fact, controlled solely by the relationships existing between the
thread turns on the preparation and locking portions, respectively,
any variances in the nut thread form are of little or no
significance.
The form of locking action obtained pursuant to engagement of the
thread turns on the locking portion with the reshaped internal
threads of the female member may be of various known types. One
novel form of locking, envisioned by the present invention, is the
employment of a bulging flank configuration on either the locking
portion of the male fastener, or the internal thread, or both,
which will produce relative flank displacement, and the necessary
interference to attain locking. Another form of locking is obtained
by providing the thread turns on the locking portion with the
standard thread form having the pitch diameter greater than the
effective pitch diameter of the sizing threads, and
correspondingly, greater than that of the reshaped internal thread
turns to be engaged therewith. As such, flank-to-flank interference
will be obtained along the opposed flanks of the locking thread
turns.
It must be emphasized that the type of locking engagement obtained
with the present invention may vary, and various known forms of
thread locking systems may be employed. The critical feature is the
reshaping of the internal thread of the female member prior to
locking engagement so as to eliminate any variables occassioned by
the thread tolerances encountered.
As to the preparation section, the thread form employed can be any
of those known in the art and used in self-tapping fasteners
wherein the internal or female thread is cold formed or cut. With
the present invention, the cold forming operation is preferred, and
as such, a radially relieved thread configuration for the
preparation section has been illustrated in the drawings. This
thread form is of a trilobular design, such as disclosed in detail
in U.S. Pat. No. 3,195,156, issued to Harvey F. Phipard, on July
20, 1965. It must be kept in mind that other known types of cutting
threads or radially relieved cold forming threads may be utilized.
It is important only that the threads on the preparation section be
capable of effecting the desired reshaping or sizing of the
internal threads to eliminate the variables due to nut thread
tolerances.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side, elevational view, partially in section and
partially broken away, illustrating a fastener member and locking
arrangement according to the present invention employed in holding
two members in assembled relation;
FIG. 2 is a partial, longitudinal sectional view of the male
fastener member and the nut of the locking arrangement of FIG. 1,
illustrated in an enlarged scale and in disassembled relation;
FIG. 3 is a partial, longitudinal, sectional view on still a larger
scale of the male fastener member and nut of FIGS. 1 and 2, in
assembled relation, and illustrating the type of locking action
obtained thereby;
FIG. 4 is a longitudinal, partial, sectional view of a fastener
member having a thread configuration constructed in accordance with
another form of the present invention;
FIG. 5 is a side view, partially broken away, of a locking screw
according to one form of the present invention;
FIG. 6 is a longitudinal cross section of FIG. 5 locking screw
engaged with a female member;
FIG. 7 is a side view, partially broken away, of another locking
screw arrangement according to the present invention;
FIG. 8 is a longitudinal cross section of the FIG. 7 locking screw
engaged with a female member and illustrating the locking action
obtained;
FIG. 9 is a side view, partially broken away, of yet another
locking screw according to the present invention;
FIG. 10 is a transverse cross section through a locking screw
according to one form of the present invention together with a
female member engaged thereby illustrating of a tri-lobular
configuration;
FIG. 11 is a longitudinal cross section of a locking screw
according to FIG. 9, together with a female member engaged thereby,
as taken, for example, at 11--11 in FIG. 10;
FIG. 12 is a similar longitudinal cross section of still another
locking screw according to the present invention, together with a
female member engaged thereby;
FIG. 13 is a plan view of a thread-rolling die of the present
invention, and of the type used to produce fasteners such as
illustrated in the foregoing FIGS. 1-12; and
FIGS. 14-16 are sectional views taken along the line 14--14 of FIG.
13, and illustrating die constructions according to the present
invention capable of producing the fasteners of FIGS. 5, 2, and 4,
respectively.
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS
Referring to the drawings, and initially to FIGS. 1-4, there are
disclosed two embodiments of the present invention, wherein a
standard thread form is employed in the preparation portion of the
fastener. The embodiment of FIGS. 1-3, differ from that of FIG. 4,
in the thread form utilized on the locking portion of the fastener,
and correspondingly, in the type of locking action obtained.
Considering now FIGS. 1-3, in FIG. 1, a fastener arrangement in
accordance with a first embodiment of the invention is shown in an
assembled relation. Said arrangement includes an externally
threaded male element or screw 10, having a driving head 12 and a
shank portion 14 with a thread form 17 and a tapered work entering
end 16.
The unthreaded segment of the shank, is designated 13 and is known
in the art as the "grip." The grip 13 extends through aligned
apertures 11 in the illustrated plate members 15, such that said
plate members 15 are maintained in abutted relation by the fastener
head 12 and a nut 26 engaged with the thread form 17.
The locking action between the nut 26 and the thread form 17
attained by the present invention, and detailed hereinafter,
maintains the nut in position and assures that same will not work
loose.
FIG. 2, illustrates a preferred arrangement of the thread form 17
for the fastener 10, with the nut 26 shown in disassembled relation
thereto. Thread form 17, includes a preparation portion "A" and a
locking portion "B," the former including a plurality of sizing
thread turns 17A, capable of cold working and reshaping the
internal thread 27 of nut 26, the locking portion having one or
more thread turns 17B for effecting a locking action with the said
reshaped internal thread 27. This locking action is illustrated in
FIG. 3, and will be discussed in detail hereinafter.
With specific reference to FIG. 2, the thread 17 illustrated
therein is of a generally standard form. That is, the following
flank 22 and the lead flank 24 are substantially straight or flat
in profile, and define an included angle of 60.degree..
As mentioned previously, the thread turns 17A on the preparation
portion "A" are of the radially relieved type, and preferable
tri-lobular, as illustrated in FIG. 10 and thereby capable of
resizing the internal thread of nut 26. In this regard, the thread
crests 23 and thread roots 25 define helices of a somewhat
irregular configuration, as a plurality of circumferentially
disposed lobes are provided due to the tri-lobular configuration.
This configuration is that as taught by the aforementioned U.S.
Pat. No. 3,195,156, and is discussed in detail hereinafter with
reference to FIG. 10. The thread turns 17B on the locking portion
"B" of the screw 10, may be either of a tri-lobular form, or of a
circular cross section. With the tri-lobular form, the radial
relief provided reduces the driving torque; however, with a
circular form, an increased locking action will be obtained,
although the driving torque may be higher. In either case, the
thread will be rolled, and the final cross sectional form of the
thread turns will be controlled by the initial configuration of the
blank, as is well known in the art.
More specifically, considering the operation of the fastener 10,
the sizing thread turns 17A on the preparation section, although of
the radially relieved type, have a given effective pitch diameter
or pitch line indicated by the datum line 28. It must be kept in
mind that in the illustrated form threads 17A are tapered, to
provide a lead-in and gradual reshaping action. Therefore, the term
"effective pitch diameter" as employed herein and designated 28,
denotes the maximum pitch diameter of the thread turns 17A, i.e.,
that of the thread turns or turns on portion "A" having the
greatest crest height. Should a straight thread form be employed
for thread turns 17A, as is within the scope of this invention,
then the standard pitch diameter and the effective pitch diameter
would coincide.
The internal thread 27 on nut 26, will also have a given pitch
diameter, indicated by datum line 29, which falls within a
prescribed range or tolerance. In forming the fastener 10, the
standard industry accepted tolerances for a corresponding internal
thread 27 is taken into consideration, and the effective pitch
diameter 28 of the sizing thread turns 17 on the preparation
section "A" is adjusted such that same is at least as great, and
preferably greater than the maximum allowable pitch diameter 29,
permitted pursuant to said standards. Accordingly, as the sizing
thread turns 17A engage the internal thread 27, said internal
thread will be worked and reshaped to a desired configuration
determined by said radially relieved sizing thread turns 17A.
Thread turns 17B on the locking portion "B," are preferably formed
as a straight thread having a pitch diameter, indicated by datum
line 30. The pitch diameter 30 is selected such that it is greater
than the effective pitch diameters 28 of sizing thread turns 17A,
by a predetermined valve indicated at 32, in FIG. 2. Accordingly,
relative to the thread turn 17A having the maximum crest height,
respective portions on the thread flanks 22 and 24 of thread turns
17B will be disposed radially upward a distance equal the
difference in the respective pitch diameter, i.e. distance 32.
Directing attention now to FIG. 3, the locking operation obtained
upon engagement of the reshaped internal thread 27 with thread
turns 17B is illustrated. In this regard, the overall form of the
reshaped internal thread 27, and correspondingly the resultant
pitch diameter 29, are controlled by the dimensions of the sizing
thread turns 17A. As such, the pitch diameter 30 of the thread
turns 17B will exceed the pitch diameter 29 of the thread 27, by an
amount approximately equal to the previously discussed distance 32.
As a result of this difference in pitch diameter, and due to the
controlled form of the reshaped internal thread 27, the lead and
following flanks 22 and 24 of thread turns 17B, will be displaced
upwardly relative to the corresponding flanks 68 and 74 of said
internal thread 27. Upon engagement, as shown in FIG. 3,
interference in the form of flank-to-flank engagement with be
obtained, with the respective flanks of the internal thread 27
being deformed to correspond to the shape of thread turns 17B.
In FIG. 3, the configuration of the lead and following flanks 74
and 68 of the internal thread are illustrated in dotted outline,
while the flanks 22 and 24 of the thread 17B are in solid outline.
As such, it can be seen that along each flank interface a
prescribed degree of interference, designated by reference
character 40, is obtained. The degree of interference 40, thus
achieved, produces the locking action imparted to the engaged
threads 17 and 27.
From the preceeding, it can be appreciated that due to the resizing
accomplished by thread portion 17A the relative form of the
internal thread 27 will be consistent, upon engagement with the
thread turns 17B, regardless of the variances in the form of said
thread 27 before engagement. Thus, the degree of interference 40
and correspondingly the locking action obtained depends upon the
relative dimensional difference between thread portion 17A and 17B,
which can be selected and varied in the design and forming of
external thread 17. It follows then that a manufacturer of
fasteners can, by utilization of the present invention, predict and
control the locking action obtained during use of the fasteners
10.
In FIG. 4, an alternate configuration for the thread form 17 is
disclosed and to avoid repetition and confusion wherever possible,
reference characters identical to those used in FIGS. 1-3 are
employed. Basically, the configuration and operation of the thread
turns 17A on the preparation portion "A" are the same as discussed
above with regard to FIGS. 1-3. The primary difference with this
embodiment lies in the form of the thread turns 17B and type of
locking action thus obtained. While these features of the thread
form 17B of this embodiment, as discussed briefly in conjunction
herewith, a more detailed discussion of the type of locking action
will be given with regard to FIGS. 5-12. It should be noted, that
in this embodiment the effective pitch diameter of the sizing
thread turns 17A and that of the locking thread turns 17B and are
the same, being designated 28. While the thread profile of thread
turns 17A is of a standard form, the thread turns 17B are of an
irregular shape having lead flanks bulged outwardly in an axial
direction, with the opposite following flank being depressed in the
same direction by a generally similar amount.
The above mentioned irregular shape of the locking thread turns of
this embodiment, is best understood with reference to the thread
profile designated 17B. The dotted outline of a thread profile
corresponding to that of thread 17A, is superimposed over said
thread profile 17B. From this it can be seen that the net result is
that the respective lead and following flanks 24 and 22, have been
displaced in an axial direction toward the sizing thread portion
"A," with the maximum amount of bulge taking place approximately
along the pitch diameter 28.
In operation, the thread 17 is fabricated such that the effective
pitch diameter 28 is as great, or greater than the maximum
allowable pitch diameter of a corresponding nut (not shown) to be
engaged therewith. Upon engagement of sizing thread turns 17A with
said nut, the internal thread will be reshaped to a specified
configuration determined by said sizing thread portion A.
Subsequently upon engagement of the irregular shaped thread turns
17B with the reshaped internal threads of the nut, said internal
threads will be deflected and a preselected and determinable flank
interference will be obtained along the interface of the lead flank
24, which produces the locking action. Due to the depressed nature
of the following flank 22, little or no interference will be
encountered, along this interface.
Thus, as was the case with the embodiment of FIGS. 1-3, with the
present form of the invention, the locking action can be predicted
and controlled by adjusting the relative dimension of the thread
turns 17A and 17B. Also, due to the sizing operation preferred by
the preparation portion 17A any variables that might be encountered
due to nut thread dimension variances are eliminated.
The embodiment of the invention illustrated in FIGS. 5 and 6,
differ from those previously discussed, in that only a locking
thread formation is employed, there being no sizing or preparation
portion to rework the internal thread of the nut and eliminate the
variable due to the industry accepted tolerances. In this instance,
the fastener illustrated employs a type of locking thread similar
to that discussed briefly with regard to FIG. 4, with the exception
that the following flank is bulged and the lead flank depressed,
opposite to that as shown in FIG. 4. Here again, wherever possible,
fastener elements have been designated by the same reference
character employed previously, with the addition of a prime
designation (') to all of the reference characters employed in
FIGS. 5 and 6.
Referring to FIG. 5, a screw indicated generally at 10' is shown
having a driving head 12', shank 14', and a tapered work entering
end 16'. The driving head 12' represents only one form of driving
end since the screw may be a headless stud or a set screw. The
screw shank is provided with a straight thread formation 17'
adjacent the tapered work-entering end, while the remainder 13' of
the shank between the thread formation and the driving head 12' is
unthreaded, and may be termed the grip. It is understood the
last-mentioned shank portion 13' is intended for extension through
an apertured structural member or the like secured against a
workpiece or nut by the head of screw 10'.
A following thread flank 22' in thread formation 17' bulges axially
outwardly, e.g. it is convexly curved in cross section, in a
direction toward driving head 12' for at least one thread
convolution. The leading flank 24' is then depressed or relieved.
For example, the leading flank is deflected concavely in a
direction away from the work-entering end for at least one thread
convolution. The aforementioned bulge and relief on the opposite
sides of each thread cross section are relative to the crest and
root portions of the thread formation, or relative to straight
lines describing the positions of conventional straight flanks
between crest and root. Normally, the bulging and corresponding
depressions are present throughout at least several convolutions of
the thread form.
With a thread form circular in cross section, the thread crest 23'
and thread root 25' will comprise uniform helices adapted to have a
predetermined mating relation with a given female thread, for
instance, a standard 60.degree. included angle thread. The flank
deviations of the present invention, which are substantially axial
of the screw, are maximum approximately along the pitch line 30' of
the screw with the thread cross-sectional widths along the pitch
line being approximately half of the thread pitch. Thus, the
outwardly bulging condition of the thread flank 22', for example,
will correspond to a substantially equal amount of relief or
depressed condition of the opposite flank 24'.
As hereinafter more fully explained, the screw of FIG. 5 is adapted
for deflecting or swaging an already existing female thread in a
nut or workpiece to provide firm flank engagement with such female
thread, and tension between a following female thread flank and the
head of the screw. As the outwardly bulged following flank 22'
engages a female thread, it deflects the female thread into a shape
corresponding with that of the following flank 22' thereby
establishing a firm pressure area against the following flank of
the female thread.
FIG. 6, further illustrates the locking operation of the screw 10'
with a nut 26'. It is understood that the screw 10' has advanced in
the direction of arrow 77', i.e., from the left to right in the
drawing, into a previously threaded nut 26'. The thread flanks
bulge in a direction opposite to the direction of advance of the
screw. It is further understood that the female thread, before
insertion of the screw, is typically round in cross section and
standard, having been previously tapped, and has the same pitch as
the male thread on screw 10'. Its thread is suitably one providing
a standard clearance fit with a standard screw having the same
crest and root dimensions as the present screw. The screw thread
according to the present invention may be round in cross section,
departing from the standard thread form principally as regards the
bulging and relieved thread flanks. The clearance between male and
female parts can be as great as will still provide substantial
pressure contact between the same male and female flanks as herein
described, that is, the axial bulge should exceed the maximum
tolerance for both external and internal threads of the general
class comprising the screw and the nut or workpiece, plus any
allowance therebetween, permitted for a conventional clearance fit.
Alternatively, the screw thread may be slightly oversize in
dimension as regards the thread of the nut as hereinafter described
in connection with subsequent embodiments.
As illustrated in FIG. 6, male threads 52', 54', and 56' have each
deflected the female thread of nut 26' to produce a depressed,
relieved or concave following flank, and a bulging leading flank,
by a deflecting or swaging action. Thus bulging following flank 62'
of screw thread 54' has produced a relieved following flank 68' on
the female thread by swaging action, urging metal of the female
thread to the left along pitch line 30'. Therefore, a bulging
female leading flank 74' is produced which nearly "fills in" the
relieved leading flank 76' of screw thread 56'. Similarly, a
bulging leading female flank 64' is established adjacent relieved
screw flank 66'. As a result of the male thread relief on the
leading flank thereof, a space is thus provided for reception of
the metal of the female part which has been moved to the left by
the swaging action, and binding or galling is thereby avoided. A
deflection of the female thread may be restricted to remain within
the elastic limits of the material from which nut 26' is
constructed, but this is not necessarily the case. The original or
undeflected position of the female thread is illustrated by the
straight, dashed lines 69' and 75' in FIG. 6.
At the location of contact between the bulging screw thread flank
and the relieved female thread flank, e.g., along adjacent flanks
62' and 63' in FIG. 6, intimate engagement is necessarily present,
since screw thread flank 62' is responsible for the exact formation
of female flank 68'. In other words, appreciable interference is
present along the interfaces of the flanks 62' and 68', with an
interference also being present at least at the top and bottom of
the following screw flank 64', i.e., at points 70' and 72'. The
intimate and extensive flank contact is provided, however, without
deforming the female thread to an extent or at a location where
galling might take place.
As can also be seen, the pressure against the female 68' 68'is in
the direction of screw head 12'. Thus, as the screw is drawn up
tight, the following female flank 68' is placed in tension toward
the screw head.
Referring to FIG. 7, still another embodiment of the invention is
shown. This embodiment is similar to the two previously discussed
embodiments of FIGS. 1-4 in that the fastener, designated 110, is
provided with a sizing or preparation portion "A" and a locking
thread portion "B." Similarly, with the fastener 110, the
preparation portion "A" will reshape the internal thread of the
nut, thus eliminating any variables in thread form occassioned by
the nut thread tolerances that may be encountered due to industry
accepted standards or tolerances. However, it should be noted that
these variables are eliminated in a manner somewhat different than
that employed with the fasteners of FIGS. 1-4.
More specifically, the fastener 110 will deflect the internal
thread of the nut to attain a desired deflection or swaging of the
thread to axially displace the thread flanks. This should be
compared with the reforming of the threads to a standard profile
with enlarged thread dimensions as was done by the fastener of
FIGS. 1-4. The deflected internal thread is then engaged with the
thread turns of the locking portion to attain the desired locking
action.
As such, a fastener 110 is provided, having a driving head 112 or
other form of driving end, a shank 115, and a work-entering end
116. The thread formation on the screw is divided into two
portions, the preparation thread portion A, the end of which is
tapered toward work-entering end 116, and the locking thread
portion B. The remainder 117 of the shank or the grip, which may
extend through an apertured structural member or the like, is shown
broken away.
A leading thread flank 118 in preparation portion A bulges axially
outwardly, e.g., is convexly curved in cross section for at least
one thread convolution in a direction axially away from driving
head 112. The following flank 120 is then relieved; for example,
the following flank is depressed concavely away from the screw's
driving head. The described condition is desirably present
throughout portion A. The second thread portion B suitably
comprises a substantially standard thread form having substantially
flat or straight flanks. In any case, as viewed in FIG. 7, the
thread flanks in section B are located to the left of the position
of thread flanks in section A, if the thread crest and root
portions in the two sections were juxtaposed for comparison.
The thread on screw 110 desirably has substantially the same lead
throughout the thread formation. Thus, the bulges and depressions
in the thread are relative to substantially standard, uniform crest
and root helices which are maintained approximately the same
through the thread formation and adapted to have a predetermined
mating relation with the female thread, e.g., a standard clearance
fit with a standard nut thread. The flank deviations from the
standard screw are maximum along the pitch line of the screw. Also,
the width of the screw thread cross section is desirably maintained
equal to approximately half the thread pitch.
The preparation portion A of the FIG. 7 screw deflects or swages
the existing thread in a nut or workpiece in a direction axially
away from driving head 112, as portion A is driven into the nut or
workpiece. After the female thread is deflected to the right by
thread portion A of the screw, the second thread portion B engages
the female thread and the following flank thereof establishes
pressure against the following flank of the female thread which was
theretofore deflected by preparation portion A. The previously
deformed following flank of the female thread is thus placed in
tension between the following flank of thread portion B and driving
head 112, as driving head is tightened. The flank-to-flank contact
thereby established is appreciable more extensive than in the
normal screw and nut combination.
FIG. 8 illustrates locking of screw 110 with a nut. In FIG. 8, only
one thread, 150, of a preparation thread portion A is illustrated,
while a pair of threads, 146 and 148, correspond to portion B in
FIG. 7. It is understood that the female thread is typically
standard and formed to conventional, accepted tolerances, as in the
previous embodiment, suitably provide a standard fit with a
standard screw having the same crest and root dimensions as the
present screw. The screw thread may be round in cross section and
may be slightly oversize in dimension as regards the dimension of
the thread of the nut, as hereinafter described. The general
configuration of thread portion B exemplified by threads 146 and
148 corresponds to a standard or typical male thread adapted for
engaging the nut thread. Thus, the flank-to-flank angle for threads
146 and 148 is 60 degrees, and the crest and root portions 129 and
136 have a conventional relation to the pitch line 30.
As illustrated in FIG. 8, preparation thread 150 having a bulging
leading flank 118 has deflected the female thread to produce a
relieved or concave leading flank 154 by a swaging action,
deforming the flank 154 to the right. The original or undeflected
position of the female thread is illustrated by dashed lines 153 at
the right in FIG. 8. In the course of reaching the position
illustrated in FIG. 8, thread 150 has similarly deflected the
preceding female thread axially to the right. Thus, flank 156 will
have been similarly deflected to the right during at least the
previous revolution of the screw. The female thread is displaced
from left to right producing bulging following flank 158, e.g.,
which is convexly rounded away from the screw's driving head, early
"filling in" the relieved flank 120 accommodating the material from
the female thread swaged to the right.
When thread 148 moves into the previously distorted female thread,
it tends to deflect the female thread to the left in FIG. 8.
Therefore, the following flank 162 of the internal female thread
will necessarily be in intimate contact with the following flank
160 of the screw since the screw thread portion A swages the final
surface configuration of the female thread. Inasmuch as a flat
screw thread flank from section B has not yet encountered female
thread flank 158, to force material to the left, some gap or space
will remain between the leading flank 159 on the screw thread, and
flank 156 of the female thread. Then as hereinbefore mentioned,
thread 148 swages remaining female threads to the left. The
material swaged to the left along the pitch line produces a female
flank 165 for nearly "filling in" along the straight leading flank
of screw thread 146.
As a result of the swaging of the female thread to the right and
then the re-forming of the same to the left, appreciable
interference is produced along the faces of flanks 160 and 162, for
example. Since the form or degree of deflection upon engagement
with the screw thread 14B is determined solely by the preparation
portion A, regardless of the original dimensions of said female
thread, the tolerances employed in forming said female thread will
have no effect on the locking action. The female following flank,
for example flank 162, is placed in tension between following flank
160 of the male thread and the head 112 of the screw. Locking is
accomplished primarily on the flank area by bending of the female
thread along the pitch line, and regions of the threads where
galling or breaking would more likely occur, are avoided. Thus, the
crest and root portions of the male thread are not materially
deflected from their normal position, and there is therefore less
tendency for the female thread crest and root portions to be broken
or damaged. Galling is also avoided, as hereinbefore mentioned, as
a consequence of the following flank relief on thread portion A.
The fastener results in desired tension and reduced driving torque
as compared with prior locking screws. In this embodiment,
increased working of the female thread, with the female threads
being returned substantially to their original position for
locking, results in increased locking strength and high removal
torque.
Referring now to FIG. 9, still another embodiment of the present
invention will be described with reference to a screw indicated at
210 having a driving end 212, a shank 214, and a work-entering end
216. In this instance, the thread formation on the screw is divided
into three portions: a preparation thread portion A which is
generally tapered toward work-entering end 216, a transition or
identification thread portion B, and a locking thread portion C.
The remainder of the shank between locking thread portion C and
driving end 212, i.e., the grip, is shown broken away. It is
understood that this part of the shank is again intended for
extension through an apertured structural member or the like
secured against a workpiece or nut by screw 210.
The preparation portion A of this embodiment functions in the same
manner as that discussed with regard to FIGS. 7-8 to eliminate
female thread variables which might effect locking. A leading
thread flank 218 in preparation portion A bulges outwardly or is
convexly curved in cross section in a direction axially away from
driving end or head 212 throughout at least one convolution, and
desirably throughout thread portion A. The following flank 220 is
then depressed or relieved, for example the following flank is
depressed concavely away from the screw's driving end or head.
Transition thread portion B suitably comprises a substantially
standard thread form having substantially flat or straight thread
flanks. However, the locking portion C comprises a thread formation
wherein the thread flanks deviate from standard threads in an
opposite direction from the thread flanks in preparation portion A.
Thus, a following flank 222 bulges or is convexly curved in cross
section throughout at least one thread convolution toward driving
end or head 212. The leading flank 224, on the other hand, is
correspondingly relieved or concavely depressed in the direction of
the screw head. The same configuration is preferably followed
substantially throughout all convolutions of portion C.
It should be noted that the thread on screw 210 desirably maintains
substantially the same lead throughout the thread formation. Thus,
the aforementioned bulging regions of portions A and C, and the
corresponding relief on the opposite sides of each cross section,
are relative to substantially standard and uniform crest and root
helices maintained approximately constant throughout the thread
formation and adapted to have a predetermined mating relation with
a female thread. The flank deflections in directions substantially
axial of the screw are maximum approximately along the pitch line
of the screw, and merge gradually with the substantially
undeflected crest and root portions of the same thread formation.
Moreover, the cross-sectional width of the thread along the pitch
line generally remains approximately half the thread pitch whereby
a bulge on one thread flank will correspond to a substantially
equal relief on the opposite side of the same thread cross
section.
The screw of FIG. 9 suitably deflects or swages an already existing
female thread in a nut or workpiece first in a direction axially
away from driving head 212 as preparation thread portion A is
driven into the nut or workpiece. The thread preparation thereby
accomplished renders the subsequent locking operation more certain
and consistent between male and female members having considerable
variations in tolerance. The preparation makes sure that the female
threads are in position for subsequent optimized engagement on the
opposite side thereof by the male locking thread. Thus strong
flank-to-flank contact is assured throughout 360 degrees as the
screw deflects the female thread in an opposite direction toward
driving head 212 when locking portion C engages the female thread.
The following flank 222 establishes a firm pressure engagement
against the adjacent flank of the female thread which was itself
theretofore deflected by preparation portion A. The previously
deformed flank of the female thread is placed in tension between
the following flank of thread portion C and driving head 212, as
driving head 212 is tightened against a member secured against the
nut or workpiece by screw 210. The flank-to-flank contact
throughout 360 degrees established in thread portion C is extensive
and optimizes the locking or holding ability of the screw in the
total tolerance of the tapped nut.
With the embodiments discussed to this point, and those of FIGS.
11-12 to be detailed hereinafter, the thread form of either the
preparation section A, the locking section B, or both, may be of a
standard, round cross section, or of the radially relieved type.
Where a considerable amount of reshaping is anticipated, the
radially relieved type of thread form is especially desirable for
the preparation portion A, as it will reduce the driving torque
during deformation of the internal thread. Conversely, with regard
to the locking portion B, the greatest locking action will be
obtained with a circular thread form. Therefore, a manufacturer can
adjust the form of the respective thread portions A and B to suit
the intended use to which the fastener is to be employed.
While various types of radially relieved threads are known such as
disclosed in U.S. Pat. No. 3,426,642 and the aforementioned U.S.
Pat. No. 3,195,156, a preferred thread cross section exhibiting
radial relief is illustrated in FIG. 10. While the cross section of
FIG. 10 is of particular value for the screw of FIGS. 1-4, and 9,
since the work accomplished in reshaping the female thread is
appreciable, nevertheless, the same cross section can be used if
desired for the other screws disclosed.
Referring to FIG. 10, a screw of the radially relieved type
referred to above engages a female thread in a female member here
comprising a nut 226, illustrated as partially broken away. The
thread formation on the screw is of arcuate polygonal cross
section, and in particular of arcuate, triangular cross section, a
form which is termed tri-lobular as set forth in U.S. Pat.
3,195,156. Line 228 indicates the peripheral or crest edge of the
screw thread, line 229 the root of the thread, and dotted line 230
represents a cross section of the pitch cylinder of the thread. The
pitch cylinder is not round, but is of arcuate, polygonal cross
sectional configuration. The line 232 represents the root of the
thread in the nut 226.
The radius of circular line 232 corresponds to the distance between
the screw axis 234 and the outermost points of screw thread lobes
236, 238, and 240. Only these lobes 236, 238, and 240 are in
relatively complete contacting engagement with the female thread.
The relatively broad sides 242, 244, and 246 will be supported out
of engagement to provide the aforementioned radial relief.
Accordingly, frictional resistance between the screw and the nut is
reduced. The lobes 236, 238, and 240 merge smoothly and gradually
with arcuate sides 242, 244 and 246 therebetween with the arcuate
radii or curvature of sides 242, 244, and 246 being appreciably
larger than the arcuate radii of curvature of lobes 236, 238, and
240. The degree of eccentricity depicted for the tri-lobular
configuration in FIG. 10 is by way of illustration only and may be
greater or less than shown. The screw according to the present
invention is preferably hardened more than the nut 226.
FIG. 11 further illustrates the locking operation of the FIG. 9
screw with a nut or workpiece. For the purposes of convenient
illustration, the transition portion B here comprises a single
thread 248 preceded by a preparation thread 250 and followed by a
locking thread 252. It is understood that screw 210 as illustrated
has advanced in the direction of arrow 277 from left to right into
nut 226. It is also understood that the longitudinal cross section
viewed in FIG. 11 may be considered as taken at the lobe of the
screw thread, i.e., at 11--11 in FIG. 10 if the screw has the FIG.
10 transverse cross section, at which location approximately a
tight fit occurs. Such fit would be uniform around the screw in the
case of a round screw.
Typical pitch diameter tolerances for a previously tapped nut and
screw in accordance with FIG. 11, and in the case of a particular
example of 5/16 inch -18 thread size, are given as follows:
Min. Max. Nut, standard class 2B 0.2764 -- 0.2817 inch (example
5/16"-18) Lock Screw 0.2817 -- 0.2837 inch
In the case of a lock screw having the FIG. 10 cross section, the
pitch diameter is measured at the lobes. Of course, the same
dimensions may apply to a round screw. It is to be understood that
for a nut of the above given dimensions, the comparable standard
dimensions for a round screw, standard class 2A size 5/16 inch -18
threads per inch, are 0.2712 inch min. and 0.2752 inch max.
These preferred tolerances set forth above thus indicate the screw
thread lobes suitably produced from a tight to an interference fit.
While these tolerances are typical and preferred, it is understood
the present invention is not limited to a tight or interference fit
at the lobes of a screw. It is further understood that the female
thread is initially typically standard and round in cross section.
Also, the general form of the male threads, for example in the
screw transition thread portion corresponds proportionately to a
typical male thread for engaging such internal or female thread of
the standard nut. Thus the included angle between the flanks of
thread 248 in the transition thread portion in FIG. 11 is typically
60.degree..
As illustrated in FIG. 11, wherein a tight fit is assumed for
purposes of illustration, preparation thread 250 having a bulging
leading flank 218 will have deflected the female thread to produce
a relieved or concave leading flank 254 by a deflecting or swaging
action, deforming the flank 254 to the right as illustrated. The
original or undeflected position of the female thread is
illustrated by dashed lines 255 at the right in FIG. 11 for
comparison. Also, in the course of reaching the position
illustrated in FIG. 11, thread 250 will have similarly deflected
the preceding female thread axially to the right, or away from the
screw's driving head. Thus, flank 256 will have been similarly
deflected to the right during at least the previous revolution of
screw 210 illustrated. The female thread will have been displaced
from left to right producing the bulging following flank 258 which
is convexly rounded in a direction away from the screw's driving
head, substantially "filling in" the relieved flank 220 of screw
thread 250. Thus, the width of the nut thread along the pitch
diameter 230 remains the same as before deflection.
However, when trasition thread 248 moves into the previously
distorted female thread, it may tend to deflect the female thread
to the left in FIG. 11. Thus, the following straight flank 262 on
the female thread. It will be apparent that the following flank 262
will necessarily be in rather intimate contact with the
aforementioned following flank 260. However, since a flat
transition screw thread has not yet encountered female thread flank
258 to force material to the left, a gap or space 257 will remain
between the leading flank 259 of thread 248 and flank 256 of the
female thread.
Locking thread 252 is effective for displacing the female thread
flank to the left, for example to the left of dashed line 266 in
FIG. 11, the dashed line being indicative of the original position
of the female thread. Bulging following flank 222 of locking thread
252 deflects the female thread toward the driving head of screw
210, producing a relieved concave flank surgace 268 in the femlle
thread. At this thread location, and at the location of following
threads of the locking thread portion, intimate engagement between
adjacent flanks, i.e., screw flank 222 and nut flank 268, is
substantially maximized. An appreciable area of interference is
produced along the faces of flanks 222 and 268, with interference
also being present at least at the top and bottom of following
screw flank 224, i.e., at points 270 and 272. The intereference is
produced without galling or undesired freezing of the parts
together.
While a gap is present between leading flank 224 of thread 252 and
adjacent flank 264 of the female thread, this gap is characteristic
of only the first locking thread convolution which encounters the
female thread. Since each female thread remains substantially
constant in width along the pitch line 230, female threads between
locking thread 252 and the screw driving head will "fill in" the
relieved leading flank of the screw thread. Thus, following flank
222 of thread 252 will urge the next adjacent female thread cross
section to the left along the pitch line, and so on.
Intimate and extensive flank contact is thus provided by deflecting
the female thread first in a direction axially away from the
screw's driving head without deforming the female thread to the
point where galling between the screw and the nut might take place.
Then, the female thread is deflected in the opposite direction
toward the driving head, preferably past its original location,
resulting in optimized flank contact and tension between the female
thread flank and the screw driving head when the screw is
tightened. The possible displacement of the female thread produced
by the preparation screw thread portion, and the locking screw
thread portion to provide this firm flank-to-flank contact has a
greater deflection value than could be accomplished in one step. In
other words, the female thread could not have been satisfactorily
deflected all in one direction, e.g., toward the screw head, by a
distance equaling the maximum practical deflection that can be
herein easily accomplished subsequent to female thread preparation
by the screw's preparation thread portion. Locking is also
accomplished with a change or reformation of the female cross
section, but only by bending the female thread along pitch line
230. As hereinbefore mentioned, the crest and root portions of the
female thread are substantially unaffected by deviation along the
pitch line, whereby undue interference at a location frequently
associated with galling or breaking of the nut or screw thread is
avoided. Also, as in the previous embodiments, not only is
premature or undesired freezing of the mating parts eliminated, but
driving torque is reduced. The relief opposite a bulge in a thread
cross section is instrumental in reducing torque and also in
avoiding galling. The total axial bulge (of a preparation thread
plus a locking thread) should exceed the maximum tolerance for both
external and internal threads of the general class comprising the
screw and nut or workpiece, plus any allowance therebetween,
permitted for a conventional fit. The fastener has been found to
provide a low driving torque to attain a desired tension while
maintaining maximized removal torque in the total tolerance of a
tapped nut.
An additional advantage of the various embodiments of the present
invention relates to the decreased nut spreading or dilating, based
upon a smaller thread pressure angle. The standard thread pressure
angle is 30 degrees as illustrated, for example, in the case of
transition thread 248 in FIG. 11. However, as a result of the
deflection of the female thread produced by locking thread 252, the
thread pressure angle is reduced, this angle being measured
approximately between a tangent to the thread flank and a line
perpendicular to the screw axis. In the case of a particular screw,
this angle was approximately 25.degree. as illustrated for thread
32 in FIG. 11. Therefore, the components of force directed radially
outwardly when the screw's driving head is tightened is reduced,
whereby nut spreading is minimized.
Another embodiment of a locking screw according to the present
invention is illustrated in cross section in FIG. 12, together with
the cross section of a female thread engaged thereby. In FIG. 12,
primed reference numerals are again employed in referring to
corresponding elements designated by unprimed reference numerals in
FIG. 11. In the FIG. 12 embodiment, screw 210' is provided with a
preparation thread portion exemplified by thread 274, a transition
portion, exemplified by thread 276, and a locking thread portion
exemplified by thread 278. As in the previous embodiment, the
screw's transition thread is of a substantially standard formation
and would suitably engage the female thread with a tight or slight
interference fit. Moreover, the screw threads may have arcuate
polygonal shapes in transverse cross section as illustrated in FIG.
10, or may be round in cross section. Screw 210' as illustrated has
advanced to the right as indicated by arrow 287.
The FIG. 12 embodiment differs from the previous embodiment in that
the preparation and locking threads, instead of being convexly
bulging and concavely relieved, are angularly bulging and angularly
relieved with respect to pitch line 230'. However, the crest and
root portions of the screw thread remain substantially standard and
undisplaced as before. Radially outwardly from pitch line 230',
leading flank portion 280 of preparation thread 274 makes a larger
than standard angle with a line perpendicular to the screw axis.
Thus, in a particular instance, this angle was 32.degree. rather
than the standard 30.degree.. Leading flank portion 282 radially
inwardly from the pitch line, on the other hand, makes a smaller
than standard angle with the said perpendicular, this angle being
26 degrees in the particular example. As a consequence, the leading
flank of preparation thread 274 bulges as in the previous
embodiment. In order for the following flank of thread 274 to be
relieved, following flank portion 284 radially outwardly from the
pitch line is related to the perpendicular by an angle of
28.degree. with flank portion 286 radially inwardly from the pitch
line having an angular difference of 34.degree. from the same
perpendicular to the screw axis. In each case, the total
flank-to-flank angle remains 60.degree. in the case of the flank
portions outwardly from the pitch line, or in the instance of the
flank portions inwardly from the pitch line. These particular
angular values are exemplary only.
In the case of locking thread 278, since the bulging region and
relief are reversed between following and leading flanks, the
aforementioned angles are similarly reversed as illustrated in FIG.
12. The operation of the locking screw 210' in deflecting and
re-deflecting the female thread is substantially the same as
hereinbefore described for the previous embodiment. The FIG. 13
embodiment is illustrative of the typical extent of flank bulge and
relief provided on screw thread preparation and locking portions in
this and the previously described embodiments. Thus, while the
preparation and locking thread flanks in the FIG. 11 embodiment are
smoothly curved, the angular measurements in FIG. 12 typify
approximate angles which tangents to the flank surfaces in FIG. 12
near the crest and root of the screw thread would make with the
aforementioned perpendicular line. The actual lineal deviation of
the preparation and locking threads along the pitch line with
respect to the screw driving head will, of course, vary with the
size of the screw, and the clearance which would be present between
the engaged female thread and a conventional male thread of the
same general proportions as the present screw. The greater this
clearance, the greater the deviation which will be desired for firm
contact. Quite obviously the flank variations have been in order to
more clearly illustrate the concepts involved.
Although a preferred embodiment of the invention for most
efficacious results comprises a screw with a preparation thread
portion, a transition thread portion, and a locking thread portion,
it will be appreciated that a locking screw according to the
present invention may alternatively comprise a preparation thread
portion, wherein the individual threads bulge to the right,
followed substantially immediately by a thread portion where the
individual threads bulge to the left for producing the intimate
contact between male and female threads. Or, as hereinbefore
described, the screw may employ a locking thread alone.
Although screws are generally described herein as having a driving
head, it is appreciated that a head as such is not necessary and
may be eliminated. The locking screw may have any other form of
driving means or driving end and may, for example, comprise a stud,
set screw, or the like.
Referring to FIG. 13, there is illustrated in plan view a die 308
for forming a thread of screws manufactured according to one of the
embodiments of the present invention. The FIG. 13 die is
particularly designed for the screw of FIG. 9, in that it is
divided into portions generally corresponding to the thread
portions of said screw, that is, die portion A is employed for
rolling the preparation thread portion A of the screw, and so on.
The FIG. 13 die is illustrated in partial transverse cross section
in FIG. 14 wherein the various thread-forming portions thereof are
more clearly illustrated, and wherein it can be seen the die is
substantially complementary to the FIG. 9 thread form. In FIGS. 15
and 16, die profiles are illustrated which are capable of forming
the fastneers of FIGS. 1-3 and 4, respectively. The showings of
FIGS. 13-16 are illustrative only and are not intended to be
dimensionally accurate.
In accordance with one feature of the present invention, the die
illustrated in FIGS. 13-16, is employed to roll threads in a manner
somewhat different from the methods heretofore employed. Each die
groove, for example, die groove 302 employed in the formation of a
preparation thread portion, is of substantially unchanging cross
section from the right-hand end of the die to the left-hand end of
the die as illustrated in FIG. 13. The same is true for the grooves
of the die which form the the transition and locking thread
portions. Since the screw form itself is desirably provided with
transition portion B, which form is substantially duplicated on the
die, the desired transition is provided whereby each die groove can
be milled with the same cross section all along its length.
A given screw blank is formed into a screw by engaging the same
between a die as illustrated in FIG. 13, and the surface of a
complementary die of substantially similar construction positioned
for forming or swaging the die thread form into such screw blank.
The screw blank will be disposed at substantially right angles to
the dies and at a predetermined angle with respect to the grooves
thereof, as illustrated, for instance in outline form at 304 in
FIG. 13. The screw blank will first engage the die at the left-hand
side, and will be rolled between moving and stationary dies so the
blank proceeds to the right. A given thread form cross section, as
rolled upon the blank by the die, may vary as such blank is rolled
from left to right. Thus, at a given distance from the screw head,
the blank may first engage a portion 306 of the die adapted for
forming a preparation thread therein. As the blank moves in a
direction to the right, the same thread form cross section will
successively be formed into a transition thread configuration and
then a locking thread configuration at the right-hand end of the
die. Die construction is much simpler than multi-portion dies
heretofore wherein a division between said thread-forming portions
would be made intermediate the ends of individual thread-forming
groove of the die, whereby, for instance, a given portion of the
screw blank would encounter only thread-forming grooves of a given
formation. The practice according to the present invention avoids
the necessity of changeover in milling cutters or the like part way
along a groove. Approximately the same crest and root spacings are
maintained throughout.
The dies are desirably tilted slightly in a conventional manner so
that thread forming is somewhat progressive. That is, the dies will
be further apart when they first encounter the blank, and will
gradually deepen their impression. Also, the blank employed is
desirably provided with a slight up taper in the direction of the
head so that the locking threads are slightly more pronounced than
the preparation threads.
While we have shown and described several embodiments of our
invention, it will be apparent to those skilled in the art that
many changes and modifications may be made without departing from
our invention in its broader aspects. We therefore intend the
appended claims to cover all such changes and modifications as fall
within the true spirit and scope of our invention.
* * * * *