Improvements in Wood and like Screws and in Screwed Shanks for various Articles.
Year: 1899

page_text: Date of Application, 24th Oct., 1899-Accepted, 30th Dec., 1899
COMPLETE SPECIFICATION.
Improvements in Wood and like Screws and in Screwed Shanks for
various Articles.
I, JOHN WILLIAM CALDWELL, of No. 231, West 4th Street, in the Borough of
Manhattan, County, City and State of New York, United States of America,
Inventor, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement:-
This invention relates to the construction of threaded devices-such, for
instance, as screws--and especially to that class of screws adapted for use in
wood.
The object of the invention is to provide a threaded device or screw which
not only has superior holding power to threaded devices or screws as ordinarily
constructed but is otherwise more efficient than such screws owing to the increased
rate of speed and facility with which the same may be forced into, or taken
out of, the wood, and this with less exertion and without the choking or clogging
of the threads thereof, as is the case with ordinary screw-threads, and is also
more efficient than such screws, since it may be readily started in ordinary wood
without the necessity, as heretofore, of first boring a hole therefor, thereby affecting
the holding paper of the wood, and may also be readily driven into place, thereby
avoiding the slow and tedious operation of inserting it by means of a screw-driver.
In the drawings accompanying and forming part of this specification, Figure 1
is a view of one form of device, such as a wood-screw, having this improved
construction of thread. Fig. 2 is a view of another form of such screw. Fig. 3
is a view, partly in vertical section, of a screw as ordinarily constructed. Fig. 4
is a vertical sectional view of the screw shown in Fig. 1. Fig. 5 is a vertical
sectional view of the screw shown in Fig. 3. Fig. 6 is an enlarged view of the
threaded portion of this improved screw, for illustrating the action of the wood
fibers. Fig. 7 is a similar enlarged view of the threaded portion of a screw as
ordinarily constructed. Figs. 8. 9, and 10, illustrate different forms of hooks
having shanks provided with this improved construction of threads. Figure 11
is a view of a square-headed screw or bolt embodying the improvements, and
Fig. 12 is an end view of the thread.
Similar characters of reference designate like parts in all the figures of the
drawings.
As a preface to a further description of this improved threaded device it is to he
understood that while the same is shown and described herein as a screw, the inven-
tion is, nevertheless, applicable to any kind of device having threads, some forms
of which are shown in Figs. 8 to 11 of the drawings: and therefore it will be
understood that by the term screw as used herein is to be understood any
device having threads.
"
"
In the use of the threaded devices-such, for instance, as wood-screws as
ordinarily constructed-it is found in practice that they not only require con-

page_text: siderable exertion in order to force them into the wood, but that it takes a
comparatively long time to accomplish this result owing to the necessity of first
boring a hole and to their slow speed, which latter is due, I apprehend, to the
shape and construction of the threads and points of the screw, which afford resist-
ance to the penetration of such screw. .
of the
.
In the screw as usually constructed, since the under beveled sides 2 (Figs. 3, 5,
and 7) of the threads project or extend below the peripheral edges 3 thereof they
first engage the wood and hence form resistant surfaces, necessitating that the
wood be forced out of the way, as at 4, Fig. 7, to permit the entrance
Moreover, owing
screw.
to the inclination of these beveled
under sides 2, the wood is forced downwardly and outwardly and in a direction
coinciding with the direction the screw is working, thereby tending constantly
to impede the effective action of the screw by pressing the same outward and by
choking and clogging the threads thereof. In other words, owing to the con-
struction of the thread, in order to force the screw into position the wood must
be displaced by a jamming or wedging action, and as the tendency of the wood
fibers is to return to their normal positions the threads are constantly being
pressed outward and are choked and clogged up, whereby the free action of the
screw is retarded. In addition to this, the screw as usually constructed is pro-
vided with a relatively flat or blunt conical or beveled point 5, which is ineffective
to cut its way into the wood, so that to drive the screw into position considerable
force is required since the wood must be forced out of the way by a wedging
action in order to permit the penetration of the screw, during which the wood
continues to impede the effective action of the screw by its resistant pressure
after the screw is entered. Furthermore, the edge of the thread being located
above the under surface thereof it has a tendency to strip the wood between the
threads so that its drawing and holding power is eliminated, and it therefore
becomes necessary to bore a hole substantially all the way in hard wood and
some distance in ordinary wood.
In the present improvement, in order to avoid the defects above set forth, I
have provided a device in which the point and threads are so constructed that
they will act as a cutting medium to permit the screw to cut its way into the
wood without the necessity of forcing the fibers of such wood out of the way
by a wedging or jamming action, and which threads will also operate to clear
themselves of the fibers of the wood, thereby to avoid the resistant pressure
thereof, and will assist in pulling the screw into position.
In a general way this improved threaded device embodies a thread the peri-
pheral edge of which is so located relatively to the under side of such thread
that it will first engage the wood, whereby, when such edge is formed sharp, the
thread may act with a cutting action on the wood, thereby to permit the device
to cut its way thereinto, the upper side of such thread being so formed that it
will act to clear the threads of the fibers of the wood and so permit the free
action of the device.
This improved device furthermore comprises a plurality of cutting points or
lips, whereby the effective action of the device is increased.
In practice the screw may have its core 8 conical throughout, (Fig. 2,) or it
may have such core of the same, or substantially the same, diameter throughout.
terminating in a short beveled or sharp, cone-shaped end 9, as desired. (Fig. 1.)
In the construction shown the screw-core is provided with a plurality of spiral
threads, (shown as two in number, 10 and 12.) thereby forming a double-threaded
screw, the threads being preferably of a wide or open pitch, although it will be
understood that any desired pitch may be used. Each of these threads 10 and 12
is so formed that its outer or peripheral edge 13 will first engage the wood, this
being accomplished by so forming the under side 14 of the threads that they
do not project beyond or below the plane of such edge, and which in practice
may be secured by forming the under side of such threads relatively flat, whereby

page_text: they may be in substantially the same plane as the peripheral edge of the
threads.
The peripheral edge 13 of the thread, which in practice first engages the wood,
may be formed as a sharp cutting edge, whereby it will cut its way into the wood,
the under side of the thread, owing to its formation, not impeding the action
of the device, so that the screw can be forced into the work with superior facility
and with comparatively little exertion.
Since the peripheral or cutting edge of the screw first engages the wood or
material as herein before set forth, it follows that the under surface of the thread,
while in the same relative plane with the edge and while relatively flat, as above
set forth, nevertheless must in practice be slightly above the cutting edge of the
screw or otherwise the screw on entering the material would have the entire
under surface of its thread in engagement with the material simultaneously with
the engagement therewith of the edge, so that in practice the under side of the
screw may be somewhat dipped to insure the prior engagement of the cutting
edge with the wood, this also being the case in practice with the threads located
on the beveled end of the screw of the form shown in Fig. 1, since as the surface
of the threads are relatively flat, and as the threads will usually have in practice
the same formation throughout the screw the under surfaces will therefore be
substantially at right angles to the surface of the core on which the threads are
carried; and as the threads on the beveled end of the screw are carried on a
beveled surface and are substantially at right angles to such beveled surface they
may have in practice their under surfaces so inclined or dipped as to positively
insure the prior engagement of their cutting edges with the wood, and this
throughout the length of the beveled surface of the core.
The upper sides or surfaces 15 of the threads are formed relatively steep, thereby
forming with the relatively flat under sides a relatively sharp cutting edge, and
owing to these relatively steep upper sides of the threads the tendency of such
threads is to spring or lift the fibers of the wood upwardly and in a direction
opposite to the direction in which the screw is working, and so clear the threads
and prevent the clogging thereof, whereby it follows that the screw may be forced
into the work with greater facility and less exertion than would otherwise be the
case, the tendency of the wood fibers to return to their normal positions assisting
in forcing the screw into position and to hold the same firmer.
To increase the working effect of the screw, I provide the same with a cutting
lip or point, which may project beyond or below the apex of the core. In practice
a plurality of these cutting-lips are provided and may correspond in number with
the number of threads carried by the core 8. In the present instance a pair of
such cutting lips or points are shown, cach spiral thread 10 and 12 terminating
in a cutting lip or point 101 and 12, respectively adjacent to the apex of the
screw. The outer ends of these spiral threads 10 and 12 are shown as coming
together near, or just beyond, the apex of the core S and forming two radial sharp
cutting edges or points, somewhat in the nature of wings, disposed in opposition
and in angular relation to the axis of the core and adapted to effectively and
quickly cut their way into the wood, whereby the screw will enter the work
These
with increased facility and less exertion than would otherwise be the case
cutting edges are in the nature of chisel cutting-points with the cutting edges
lower than the heel, and readily lift the wood upwardly and outwardly and
quickly form a hole to admit the core of the screw.
It will be understood that in the formation of a single-threaded screw only one
of these cutting edges or points may be provided.
In practice the screw may be provided with a relatively sharp pitch, which is
practicable in this construction of serew, whereby its speed may be increased.
It is preferable in the formation of this device that the threads around the
core should be of an open or wide pitch, though not necessarily the pitch shown
in the drawings, so that the threads, as they draw the device into the wood, will

page_text: bite the wood firmly without splitting and at the same time draw the device into
the wood at an increased rate of speed.
By constructing the screw in the manner set forth it has been found in practice
that it will enter nearly all wood without boring, and in exceptionally hard wood
by boring only a slight distance, so that the wood is left in position to hold
the screw firmer than otherwise, whereas in the use of the ordinary screw it is
necessary first to bore a relatively deep hole, which displaces and removes the
wood, so that when the screw is forced into position such wood will not hold the
screw with the same efficiency; hence its drawing and holding power to a great
extent is destroyed. Moreover, by forming a screw with a pair or a plurality
of cutting edges or points the device will cut across or through cracks, holes,
knots, &c. without altering or changing its course.
It will be seen that since in this improved screw the threads are beveled at
their upper sides in a somewhat similar manner to that in which the ordinary
threads are beveled at their under sides, it follows that the action of the wood
on this improved device, when a drawing or outward force is exerted thereon,
will be in a direction opposite to that in which it is worked-that is to say, the
upper inclined or beveled surface of the screw-threads acts to jam or wedge the
wood when an outward or drawing force is exerted on the screw in a similar
manner to that in which the wood is jammed or wedged by the under faces of
the ordinary screw when rotated into position, so that the holding power of this
screw is superior to the ordinary screw.
This improved screw is, of course, especially intended for use in wood and is
applicable for use in woods of various kinds and degrees of hardness, and is
in one form thereof especially adapted for being driven in place by means of a
hammer, thereby avoiding the slow and tedious operation of inserting the screw
by means of the screw-driver.
In driving a screw of this improved construction in this manner into the
wood the extended spiral, relatively flat, under surface 14 of the thread forms a
resistance surface against which the force of the blow is expended, and this force
being distributed over such a relatively extensive area tends to prevent the driving
of the screw downwardly, in view of the angle of the thread, with sufficient energy
to sever the fibers of the wood immediately under said resistance surface and in
the line of the edge of the thread, while at the same time this action of the
under surface, in connection with the relatively steep pitch of the thread, tends
to rotate the screw during the driving action with greater speed than it otherwise
might be rotated, and so furnishes the power for operating the cutting-points 10¹
and 12 at the apex of the screw, whereby these points are made to co-operate for
boring a hole into which the threaded portion of the screw is forced.
It will therefore be observed that the peculiar co-operation between a screw-
thread having the particular construction described and the two cutting-points is
such that this improved thread furnishes an effective means for operating said
cutting-points for cutting away the wood to form the small bore into which the
somewhat larger core of the screw will be forced by the blows to which the screw
is subjected while it is being driven into place.
In the operation of inserting the screw, the fibers of the wood, as these are
separated by the relatively sharp thread, lie, some of them, those immediately
under the thread, as a, relatively straight or, perpendicular to the axis of the
screw. Those fibers, as h, however, which naturally come just above the edge
of the screw-thread are not cut off or destroyed, as ordinarily happens with th
old kinds of screws, but are turned upwardly, so that the fibers which pass just
over the extreme edge are bent at said edge and lie inclined upwardly along the
steep surface of the thread, as at c. In other words, the lower fibers of the
inclined mass of fibers push upwardly the other fibers immediately above them,
and also push the fibers outwardly so as to form a compact mass adjacent to the
inclined upper surface 15 of the screw-thread, thereby constituting a bracing

page_text: member between said inclined surface and that region of the wood which lies
ust outside of the screw. Furthermore, this bracing action and the inclination
of the upper surface of the thread co-operate to prevent the retraction of the
screw by the pressure applied thereto in an outward direction, since this inclina-
ion of the upper surfaces of the screw-thread, which forms, to a certain extent,
a double wedge, owing to its steep inclination both downward and sidewise,
operates towards counteracting the effect which would otherwise be produced by
the relatively steep pitch of the screw-thread, which would naturally tend to
reduce the security of the fastening.
Owing to the features of construction, which I have hereinbefore more fully
pointed out, the fiber of the wood into which the screw is driven is properly
separated to form the space for the screw-thread, and this with a minimum of
destructive action on such fiber, thereby securing a superior holding power of
the screw in the wood while not retarding the introduction of the screw by driving
instead of by the use of a screw-driver to turn the screw into place.
In the use of a screw constructed in the manner set forth, it has been found
by actual test that it will penetrate ordinary wood one inch thick in about sixteen
(16) turns, while an ordinary screw for the same kind and thickness of wood
requires from thirty-eight (38) to (42) turns under equal power.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:
1. A screw comprised of a core provided with one or more threads each having
a sharp cutting edge located relatively to the under side of such thread to first
engage and upwardly displace the material, thereby to decrease the resistance
to the entrance of such thread.
2. A screw comprised of a core provided with one or more threads each having
a sharp cutting edge located relatively to the under side of such thread to first
engage and upwardly displace the material and thereby decrease the resistance
to the entrance of the thread, and each thread terminating in a cutting-lip pro-
jecting beyond and at an angle to the axis of the core.
3. A device of the class specified comprised of a core provided with a plurality
of threads disposed thereon, each thread having a beveled upper face, a relatively
flat under face, and a sharp cutting edge located relatively to the under side of
such thread to first engage and upwardly displace the material and thereby decrease
the resistance to the entrance of the thread, and each of said threads terminating
in a cutting edge or lip projecting beyond and at an angle to the axis of said
core.
4. A screw comprised of a core provided with one or more threads located
thereon and extending beyond the entering end of said core, each forming a radial
cutting lip or wing so disposed that its pitch angle is less than the angle between
the under surface of the thread and the core.
5. A screw comprised of a core cone-shaped from end to end and provided
with one or more threads each having a sharp cutting edge located relatively to
the under side of such thread to first engage and upwardly displace the material
and thereby decrease the resistance to the entrance of such thread, each of said
threads terminating in a cutting lip or wing projecting beyond and at an angle
to the axis of said core.
6. A screw having a core, cone-shaped from end to end, and a pair of spiral
threads disposed thereon, each of said threads having a relatively flat under face
and a beveled upper face and terminating in a cutting edge or point adjacent to
the end of said core.
7. The herein-described device comprised of a core provided with a cone-
shaped or beveled end and with a plurality of threads thereon, each of the threads
of such cone-shaped end having a sharp cutting edge located relatively to the
under side of such thread to first engage and upwardly displace the material and

page_text: thereby decrease the resistance to the entrance of the thread, and each of said
threads terminating in a radial cutting lip or wing projecting beyond said core.
8. A device having a core provided with a conc-shaped end and two wide
or open pitch spiral threads of the same depth throughout and extending beyond
the apex of the core and forming two radial cutting wings or points, each of said
threads having a relatively flat under face and a relatively inclined upper face.
Dated this 24th day of October 1899.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.