Improvements in Drive Screws.
Year: 1889

page_text: Date of Application, 6th Aug., 1889-Accepted, 28th Sept., 1889
COMPLETE SPECIFICATION.
Improvements in Drive Screws.
I CHARLES DAKE ROGERS of 21 Stevens Street Providence in the State of Rhode
Island United States of America Works Superintendent do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particu-
larly described and ascertained in and by the following statement :-
The invention herein described is that of a wood screw adapted to be rapidly
inserted into wood without disintegrating its fibres, either by turning it in the
ordinary manner according to the pitch of its spiral threads, or by driving it, as a
nail is driven, the screw having great strength and capacity to hold firmly, and which
can be cheaply made by rolling and without waste of material. These qualities are
secured by the peculiar form of the surface which comes from the groove and thread
which I form, and from the normal surface of the blank which I retain between tho
threads. In the ordinary wood scrow the pitch of the threads or the angle formed
by the thread with a line touching it at any point and parallel with the axis of the
screw is nearly a right angle. Such a screw when inserted into wood in the ordinary
manner by turning holds against longitudinal strain mainly by the engagement of its
threads with the wood. A smooth nail, on the contrary, holds by the adhesion of the
wood to its surface, and it is well known that if the integrity of the wood is not
impaired by the entrance of the nail, the hold is very firm.
If a screw with such a pitch of the thread is driven into wood by the blows of a
hammer like an ordinary nail, it will advance into the wood like a nail and form a hole
equal in diameter to the diameter of the screw across the threads, and there will be no
engagement of the wood with the threads of the scrow, except perhaps to a slight
degree, due to the elasticity of the wood. On the other hand, the wood is liable to be
very much ruptured. If the pitch is increased, that is, if the acute angle it forms
with a line touching it and parallel with the axis of the screw be diminished, the
difficulty of inserting it into wood in the ordinary manner by turning will be increased,
by reason of the tendency of the threads to shear the wood, and if the pitch be greatly
increased the insertion of the screw in that way becomes impossible. On the other
hand, the advance of the screw into the wood with a given turning of the screw will
increase. To secure, therefore, a quick advance of the screw into the wood, its threads
should have a steep pitch, and if the pitch becomes too great for insertion by turning,
the screw may be driven into the wood like a nail, but turning on its axis as it
advances. There is, however, a tendency of a screw thus driven to shear the wood,
and this, together with the adhesion of the wood to the metal, often causes the disin-
tegration of the fibres of the wood and diminishes its power to hold the screw,
especially if the pitch of the screw is such that, after being driven into the wood, it
may be withdrawn by turning in the ordinary manner. It is of especial importance
with screws of steep pitch that the integrity of the wood shall be preserved, for as
the pitch increases, the holding power of the wood, due to its direct engagement with
the metal, diminishes, and its dependence upon the adhesion to the metal increases.
If the fibres of the wood are broken up in the insertion of a screw, either by turning
or driving, its capacity for holding the screw is correspondingly diminished. The
tendency of a screw inserted by turning to break up the fibres of the wood increases
as the pitch increases, while its tendency to do this when driven diminishes.
But it is often desirable that a screw which is inserted by driving should be with-
drawn by turning with a screw driver or wrench, and, therefore, it must contain the
antagonistic conditions above referred to. These conditions are most nearly balanced
when the pitch of the grooves and threads is nearly at an angle of forty-five degrees
with the axis of the screw. The pitch cannot, I believe, be greatly varied from this
without destroying the capacity of a screw for being driven, or for being withdrawn

page_text: by turning, and whatever the pitch may be, and however the screw may be inserted,
it is of the greatest importance that the integrity of the wood shall not be impaired.
I have devised a form of thread and groove which, in connection with a part of the
surface of the blank left in its normal condition, secures all these conditions and gives
a screw which, according to the pitch of its threads, may be rapidly inserted and
withdrawn by turning like an ordinary screw, or it may be inserted by driving and
withdrawn by turning; while in dither case the holding capacity of the wood is
preserved. I believe all this has never been done with such practical success before as
to secure any considerable use of such screws.
The surface of my screws presents three features which are not, I believe, to be
found together in any screw heretofore made.
1st. A shallow groove impressed into the metal of a blank and having transversely
a curved form.
2d. Threads at the edges of the groove raised slightly above the normal surface of
the blank by the compression and displacement of the metal to form the groove.
3d. A portion of the normal surface of the blank between the threads, having the
same spiral inclination or pitch as the threads and groove.
In the accompanying two sheets of drawings I have represented my improved
wood-screw in several different forms.
Figure 1 is a side elevation or perspective view of a single-groove screw, the
thread extending to the point; Fig. 2 is, a sectional view taken through the longi-
tudinal axis; Fig. 3 is a transverse sectional view taken on line m m of Fig. 2,
through the plain portion of the shank; Fig. 4 is a similar view taken through the
threaded portion, on line k k of Fig. 2; Figs. 5, 6 and 7 represent modified forms of
the screw head.
Fig. 8 is a perspective view of the improved screw, having two grooves and un-
threaded point; Fig. 9 is a longitudinal sectional view, taken through the center of
the screw Fig. 10 is a cross-sectional view taken through the screw on line oo of
Fig. 9; Fig. 11 is a similar view taken on line of Fig. 9.
Fig. 12 is a perspective view of my improved screw, having a head adapted to
receive a wrench; Fig. 13 is a similar view of the screw, having the unthreaded
portion of the shank or stem cone-shape; and Fig. 14 represents a perspective view
of my wood-screw having a tapering or cone-shape threaded portion.
In the drawings, A indicates my improved screw complete, having a head of any
well-known form; the shank a immediately adjacent to the head is plain or unthreaded,
or it may be conical, as shown in Fig. 13.
The threaded portion of the screw is provided with one or more shallow spiral
concave grooves b, extending below the normal surface of the blank; the two edges
of the grooves extend beyond the normal surface of the blank, thereby forming
threads c, which continue to the point p, as shown, or the threads may terminate at
the base of the point p', as shown in Figs. S and 9. Intermediate of the grooves and
adjacent threads is the spiral surface a¹, which is a part of the normal surface of the
blank. The grooves and threads e like those 1 have described may be formed by
cutting away the metal of the blank, but I design to make them by rolling the blanks
between dies in a similar manner to that described in a U. S. patent granted to me
Sept. 20, 1887, No. 370,354, but having faces fitted especially to produce the screws
herein described, and which are the subject of an application filed herewith for a
separate patent. Although the thread c of the screw rises but slightly above the
normal surface of the blank, yet it is very efficient in advancing and withdrawing the
screw, for its surface on a radial line may be at right angles or very slightly inclined
to the axis of the screw, and its action as an inclined plane is exerted to the best
advantage to move the screw along its axis. The groove, which is efficient in con-
nection with the thread, is insufficient alone.
The spiral thread at the edges of the groove performs an important service in
enabling the wood to fill the groove without rupture or disintegration. The wood
which enters the groove is not so much compressed as that in contact with the spiral
normal surface a of the blank, and the action of the raised thread in making a defined

page_text: line of separation between the portions of the wood subjected to different degrees of
compression appears to relieve the wood in the groove from strain due to the greater
compression of the adjacent portion and allows it to take the form of the groove more
easily and perfectly and without rupture of its fibres. If the thread is omitted or
removed, the liability of the fibres of the wood to be ruptured as the screw is inserted
is much increased.
The transverse curvature of the groove (see Figs. 4 and 11) is important in
raising the thread by rolling, as it facilitates the lateral flow of the metal under the
die. It also diminishes the tendency of the blows by which the screw is driven into
the wood to break up the fibres of the wood, and facilitates the compression of
the wood so as to fill the groove completely. The cutting edge c of the thread
also facilitates the entrance of the screw without breaking up the fibres of the
wood.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
A screw provided with one or more spiral grooves impressed into the metal of
a screw blank and with spiral threads raised between the grooves and the adjacent
normal surface of the blank by the compression and displacement of the metal in
forming the grooves.
Natal ..
Tl
1000
CHARLES DAKE ROGERS,
Inventor.