U.S. patent number 3,903,764 [Application Number 05/415,781] was granted by the patent office on 1975-09-09 for minimum stressed wrench.
Invention is credited to Alfred Frederick Andersen.
United States Patent |
3,903,764 |
Andersen |
September 9, 1975 |
Minimum stressed wrench
Abstract
A wrench for use on polygonal fasteners, which wrench grips the
fastener in such a way that maximum leverage (moment-arm) is
obtained for turning the fastener, even at the sacrifice of marring
the fastener in the process. The fastener gripping surfaces being
roughened.
Inventors: |
Andersen; Alfred Frederick
(Berkeley, CA) |
Family
ID: |
23647164 |
Appl.
No.: |
05/415,781 |
Filed: |
November 14, 1973 |
Current U.S.
Class: |
81/121.1;
411/403; 81/186 |
Current CPC
Class: |
B25B
13/065 (20130101) |
Current International
Class: |
B25B
13/06 (20060101); B25B 13/00 (20060101); B25B
013/06 () |
Field of
Search: |
;81/120,121R,121B,186,119 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Smith; Al Lawrence
Assistant Examiner: Smith; James G.
Claims
I claim:
1. A wrench for turning a nut or bolt of regular polygonal shape,
said wrench having a closed cavity of subsurfaces for engaging and
turning said nut or bolt in either a clockwise or counterclockwise
direction of rotation about the central axis of said regular
polygonal shape, which subsurfaces are symmetrical with respect to
said axis when engaging said nut in either direction of rotation,
and at which times the engaging subsurfaces of said cavity are all
essentially parallel to said axis, and where during turning there
are one or more sets of such subsurfaces employed exclusively in
turning said nut in the clockwise direction and one or more sets
employed exclusively in turning said nut in the counterclockwise
direction of rotation, each such set having at least one pair of
opposing subsurfaces, and where one or more of said subsurfaces are
roughened to substantially increase the frictional resistance to
slipping between such subsurfaces and the faces of a nut or bolt
gripped by said subsurfaces.
2. A wrench of claim 1, where the roughened gripping surfaces
incorporate a series of sharp lugs.
3. A wrench of claim 1, where the roughened gripping surfaces
incorporate a series of sharp lugs whose gripping faces lie in
planes which pass through the geometric center of the wrench
cavity.
4. A wrench of claim 1, where the roughened gripping surfaces
incorporate a series of sharp lugs spaced so close together that no
appreciable indentation in the fastener takes place except under
very substantial torque approaching maximum torque.
5. A wrench of claim 1, where the roughened gripping surfaces
incorporate impregnated hard particles.
6. A wrench of claim 1, where the roughened gripping surfaces
employed in turning a fastener clockwise are substantially less
rough than those employed in turning it counterclockwise.
Description
SUMMARY OF THE INVENTION
In the past, wrenches have generally been designed to engage the
fastener in such a way that the fastener is turned without marring
the surface of the fastener, if possible. Thus, except in cases
where serrations are needed to prevent slipping, such as with pipe
wrenches and pliers, where the object being turned is essentially
round, the gripping faces of wrenches have understandably been
smooth; and in cases where the wrench cavity completely surrounds
the fastener, such as in box wrenches and socket wrenches, and thus
where there is no danger of slipping, there has been no thought of
putting serrations on the gripping faces. Thus, all box and socket
wrenches have been designed and manufactured with generally smooth
faces. And this practice has been only sensible and rational
considering that the avoidance of slipping and marring, where
possible, has been practically the sole concern in wrench designs
up to this time.
But the wrench of this invention is designed for quite a different
purpose; namely, to so grip the fastener that minimum stress is
generated in the wrench, even at the expense of marring the
fastener. Despite the fact that it applies to wrenches of the
closed type, such as box and socket wrenches, and thus presents no
need to employ serrations or other means to avoid slipping, it
employs such serrations and other means in order to transmit the
applied torque by way of an enlarged moment-arm, which in turn
results in a greatly reduced reactive force on the wrench and
reduced reactive stresses in the wrench.
In the preferred form of this invention the serrations, or other
means of generating friction between the faces of the wrench and
the fastener, are designed so as to increase the friction, and thus
increase the moment-arm, as applied torque is increased, so that
maximum moment-arm is attained at the time when applied torque is
maximum.
The practical advantage of reducing reactive stresses in the wrench
is in then making it possible to manufacture the wrench out of less
expensive material with less tensile strength, or to reduce the
outside diameter of the wrench, thus making it possible to engage
fasteners where clearance around the fastener is insufficient to
allow entry of conventional wrenches.
The details of how the wrench of this invention engages the
fastener so as to bring about greatly reduced stresses in the
wrench is explained in more detail in the following discussion of
the drawings.
IN THE DRAWINGS
FIG. 1 shows a typical section of a conventional 12-point socket,
18, and a section of a regular hexagon fastener, 19, where said
socket is applying a clockwise torque, T, to said fastener, which
torque is transmitted by way of 6 forces, of which F.sub.1 is
typical, and which forces impinge on said fastener at 6 equally
spaced portions of the fastener, of which portions portion A.sub.1
is typical, and where both the wrench cavity and the fastener are
exactly nominal size and thus fit each other exactly.
FIG. 2 shows the same as FIG. 1 except that the wrench cavity is
shown at approximately the maximum manufacturing tolerance and the
fastener is shown at approximately the minimum manufacturing
tolerance, the resulting engagement being at the corner of the
fastener as shown.
FIG. 3 shows a section of a regular hexagon fastener, 20, and a
section of an unconventional wrench cavity with lugs on the
gripping faces, of which the lug shown, 25, is typical.
FIG. 3a shows a section of a regular hexagon fastener, 47, a
section of a wrench of this invention, 46, and a typical engagement
of the fastener by the wrench at 41, 42, 43, 44, and 45 by way of
typical forces f.sub.o, f.sub.a, f.sub.b, f.sub.c, and f.sub.d
respectively at a time when indentation is taking place under the
application of substantial torque.
FIG. 4 shows a section, 43, of a variation of the wrench of this
invention, where the wrench surfaces employed in turning the
fastener clockwise are smooth, whereas the surfaces employed in
turning the fastener counterclockwise are roughened in some way so
as to generate friction between the impinging surfaces.
FIG. 5 shows a cross-section of a typical wrench of this invention,
50, engaging a typical fastener, 51.
THE DRAWINGS IN DETAIL
Again referring to FIG. 1, F.sub.R.sbsb.1 is a typical reactive
force, equal and opposite to F.sub.1, impinging on said socket
wrench at a typical portion, A.sub.1, of said wrench. The typical
wrench and fastener surfaces, extending from 12 to A.sub.1, are
smooth, as in all conventional wrenches of the closed type, and
therefore can offer no appreciable resistance to sliding on each
other. Thus, there can be no appreciable force-component in the
direction from 12 to A.sub.1 or from A.sub.1 to 12. Thus, F.sub.1
and F.sub.R.sbsb.1 must, as shown, be essentially perpendicular to
the direction determined by the impinging surfaces. That is,
F.sub.1 and F.sub.R.sbsb.1 must, as shown, be along the line
determined by A.sub.1 and 17, and thus the perpendicular distance
from O.sub.1, the geometric center of both the fastener and the
wrench cavity for the plane shown, to the line determined by
A.sub.1 and 17 must be, as shown, the distance from O.sub.1 to 17,
and this distance, then, is the magnitude of each of the
moment-arms by means of which the 6 said forces transmit said
applied torque, T, to said fastener, 19.
The magnitude of said moment-arm is, applying trigonometry, equal,
as shown, to NS/2(Tan 30.degree. ) as a maximum attainable without
friction between the impinging surfaces, where "NS" is abbreviation
for "Nominal Size," and is the nominal perpendicular distance
across the flats of the fastener.
Thus, if the total torque applied is T, then
T = 6(F.sub.1 .times. NS/2 Tan 30.degree. )
Removing the fraction we get:
T = 3F.sub.1 (NS)Tan 30.degree.
Dividing both sides by 3(NS)Tan 30.degree.:
F.sub.1 = T/3(NS)Tan 30.degree.
Rephrasing we get:
F.sub.1 = T Cot 30.degree. /3(NS)
Substituting 1.733 for Cot 30.degree.:
F.sub.1 = (1.733)T/3(NS)
Dividing we get:
F.sub.1 = 0.577T/(NS) = F.sub.R.sbsb.1
Such, then, is the magnitude of a reactive force representative of
the six reactive forces impinging on a conventional socket-type
wrench of perfect fit with an hexagonal fastener.
Such a perfect fit is, of course, impractical in practice because
no provision is made for clearance for engagement and
disengagement. The dotted lines in FIG. 1 indicate the lines along
which the wrench surfaces would more likely lie in practice, in
order to provide clearance for engagement and disengagement. Thus,
in practice, the wedging action tending to spread the typical
conventional socket-type wrench is typically greater than that
shown in FIG. 1, and might even be as great as shown in FIG. 2.
Referring to FIG. 2, if we take the moment-arm here to be roughly,
48(NS/2), as shown, and perform the same trigonometric calculations
to determine F.sub.R.sbsb.2 as were performed to determine
F.sub.R.sbsb.1, we will find that F.sub.R.sbsb.2 will equal
F.sub.R.sbsb.1 (0.577/0.48), or approximately 0.7T/NS. Therefore,
it is unlikely that the typical reactive force impinging on a
typical conventional socket-type wrench will be under the magnitude
of 0.6T/NS. We keep this in mind as we proceed to calculate what
the typical comparable reactive forces would be in a wrench of this
invention.
Referring to FIG. 3, we see here a way to secure the maximum
possible moment-arm by having the wrench exert tangential force
only, with no radial component. The result is a moment-arm more
than twice the magnitude obtained, as shown in FIGS. 1 and 2, in
the typical conventional socket-type wrench. Accordingly, the
reactive force F.sub.R.sbsb.3 would be less than half of even the
impractical conventional ideal, F.sub.R.sbsb.1. But the wrench
suggested in FIG. 3 would be impractical from another standpoint;
namely, that its lugs would tend to sheer off the corners of the
fastener, such as at 22, and would severely mar the fastener. This
brings us close to the compromise solution which constitutes the
essential feature of the wrench of this invention.
Referring now to FIG. 3a, we see here a modification of FIG. 3. All
of the forces impinging on the fastener, and all the reactive
forces impinging on the wrench are, as in FIG. 3, tangential
forces, utilizing the maximum practical moment-arm, but instead of
only one lug, there are several, the number varying with
circumstances and with desirable outcomes. The estimated resultant
of all these forces, F.sub.3a, therefore calculates to be roughly
half of what can be expected in the typical conventional
socket-type wrench. Note that the surfaces of the lugs by means of
which these forces impinge on the fastener all lie along planes
which pass through the common center, O.sub.3a, of the wrench and
the fastener. It is this feature which assures that none of the
forces will have radial components, the significance of which will
be discussed subsequently. Thus, the gripping faces of said lugs
are not parallel to each other, and are not serrations in the
common usage of that word. Strictly speaking, they are a series of
lugs, each angled with respect to the common center, rather than to
each other.
These lugs can be sized and spaced such that when only a minor
torque is applied to the fastener the lugs, shown at 41, 42, 43,
44, and 45 as typical, would not penetrate the fastener, in which
case the moment-arms and resultant forces would be roughly as shown
and calculated in the discussion of FIG. 1. However, when
substantial torque was applied, then the lugs would penetrate; the
greater the torque, the greater the penetration. Thus, these lugs
could be sized and spaced so that even though torque was
substantially increased, such increase would not increase the
reactive forces reacting on the wrench, and might even serve to
decrease them.
Since F.sub.3a is roughly half of F.sub.1 the reactive stresses set
up in the wrench by F.sub.3a would, all other things being equal,
be roughly half those set up by F.sub.1. But all other things are
not equal, for there is a further advantage of F.sub.3a over
F.sub.1 ; namely, the direction in which it impinges on the
fastener, which determines in turn the direction of the reactive
forces on the wrench, and thus the direction of the estimated
resultant reactive force, F.sub.R.sbsb.3.sbsb.a. The explanation is
as follows:
The direction of F.sub.R.sbsb.1, being largely radial, sets up
bending moments, and the stresses accompanying these, in the thin
sections of the wrench wall, whereas F.sub.R.sbsb.3.sbsb.a, having
no radial component whatever, avoids these bending moments
completely, for it is completely tangential. Thus, whereas the
forces set up in a conventional socket-type wrench tend to change
the shape of the wrench, and thereby generates substantial
bending-moment stresses, the forces set up in the wrench of this
invention do not tend to change the shape of the wrench: that is,
not at the time of maximum applied torque, which is the time when
fracture would occur if it is to occur.
Therefore, the stresses in the wrench of this invention would, from
a complex of factors, be only 1/3, or perhaps only 1/4, as great as
the stresses set up in the conventional wrench of the socket-type,
when maximum torque is applied.
The wrench illustrated in FIG. 4 is a variation on the wrench of
this invention, where in retaining smoothness for those surfaces
employed in turning the fastener clockwise, generally the
tightening direction, and the direction in which maximum torque is
not generally applied, moment-arm is sacrificed in order to
completely remove the possibility of marring the fastener. However,
some means of generating friction between the impinging surfaces is
retained for those wrench surfaces employed in loosening, for it is
in loosening, such as in loosening a corroded fastener, that the
maximum torque is generally applied, and thus it is in the
loosening (counterclockwise) direction that the frictional means
contributed by the wrench of this invention are most called
for.
FIG. 5 shows the general form of the wrench of this invention, 50,
engaging a hexagon fastener, 51, to turn said fastener clockwise by
way of gripping surfaces of which 52 is typical, and where some
frictional means are incorporated into said gripping surfaces, the
nature of which frictional means may vary from one practical
application to another and may vary between those surfaces employed
in turning the fastener clockwise, of which surface 52 is typical,
and those surfaces employed in turning the fastener
counterclockwise, of which surface 53 is typical, for the reasons
stated above.
The frictional means, other than a series of lugs, referred to
above, might include impregnating the wrench surfaces with sand
particles, carbide particles, or some other hard particles, or
simply roughing up said surfaces sufficient to generate substantial
friction.
* * * * *