Improvements in Wood Screws.
Year: 1890

page_text: Improvements in Wood 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 he performed, to be
particularly described and ascertained in and by the following statement :-
In the manufacture of wood screws it is now, as well as for some years past, the
almost universal practice to provide such screws with what is termed a
gimlet-
point," that is, screws adapted to be inserted into wood without the necessity of first
boring a hole into the wood for the screw. This type of screw is not confined alone
to cut screws, that is, screws in which a spiral groove is cut into the blank's body to
produce a thread by the aid of a cutting tool, but it also includes the more modern
or "rolled" screw, as it is termed. The latter are in some instances produced by
introducing the blanks cold between a pair of oppositely travelling dies having their
working faces provided with a series of inclined grooves and ribs. The action of these
grooves and ribs is to roll a spiral groove or crease into the blank's shank portion,
the displaced metal being at the same time gradually transformed into a raised rib or
thread having a suitable form cross-sectionally. Sometimes the threads of a rolled
screw are produced without an appreciable elongation of the blank, the thread then
being considerably larger in diameter than the normal size of the blank; again the
screw is elongated, and not enlarged laterally, by the rolling process, the diameter of
the threaded and unthreaded portions being alike, and sometimes the screws are both
enlarged and elongated by the action of the dies to which they are subjected. I
believe that in each of the methods of rolling just referred to the point portion of
screws thus produced are to a great extent imperfectly screw-threaded.
I have discovered that it is not necessary that a rolled screw shall have a screw-
threaded point in order to readily enter it into wood, one reason being that the metal
now used is more homogeneous, or less fibrous, than that formerly employed; there-
fore the thread can be made thinner and consequently sharper, so that it is more
easily inserted, because the edge of the thread readily cuts the wood as the screw is
advanced into it. This latter feature is especially noticeable when the threads are
produced by my improved dies, which form a solid thread, as clearly described in the
Specification to British Letters Patent No. 12,730 of 1887.
The improved wood screw forming the subject of my present application differs
from others of its class, in that it has an unthreaded sharpened or cone-shaped
centering end or tip formed on its point portion adapted to be inserted into wood by
a slight blow; the point portion is also provided with oppositely arranged screw-
threads commencing at the base of the tip, which extend radially and form chisel-
shape or cutting edges; from this point the two threads extend rearwardly along the
blank's body any desired distance, the screw terminating at the adjacent end in an
enlarged head provided with a slot or other suitable form by which the screw is
adapted to be inserted into the wood. The unthreaded portion of the body of the
screw uniting the head and threaded portion I prefer to make slightly tapering or
conical, thereby increasing its strength. An advantage of my improvement is that
in inserting the screw the unthreaded tip serves to first centre and steady or support
the screw laterally, after which the sharpened or chisel-pointed end of the two
threads act to cut their way readily into the wood. By the employment of the
double-thread the work or resistance opposed to the entrance of the screw is equalized
at all points, so that it is more easily and truly introduced than screws having a
single thread and unprovided with the sharpened tip and chisel-shaped thread
termination.

page_text: threaded and as made from wire, a portion of its upper portion being broken away;
Fig. 2 is a similar view of the blank after being screw-threaded, and forming my
improved rolled wood screw;
Fig. 3 is an inverted end view (enlarged) of the screw ;
Fig. 4 is a plan view;
Fig. 5 is a side view of the lower portion of a blank having its spur or entering
end polygonal or pyramidal shaped;
and
Fig. 6 is a similar view of the blank shown in Fig. 5 after being screw-threaded;
Fig 7 is an inverted end view (enlarged) showing modified forms of the pyramidal
point.
In the drawings, indicates the blank as a whole, consisting of the headed
portion h, an enlarged or tapering shank portion s¹, the cylindrical shank portions,
and the point portion p; the latter provided with a comparatively blunt part p²,
extending from the plain portions and terminating in a sharpened tipp, having the
inclination of its sides more acute than those of the proximate portion p². The blanks
are made singly from a continuous length of wire whose normal diameter is sub-
stantially the same as that of the cylindrical parts, the head and enlarged portion s¹
being formed simultaneously by upsetting the metal in a suitable die by means of a
heading machine. The nick n may also be produced at the same time. The headed
wire is next forced out of the die and fed ahead the desired distance to produce a
blank, after which properly shaped cutting-off dies conjointly sever the blank from
the wire and form the point portion p.
The blanks are next introduced to a machine which forms the double screw-
threads t upon the body of the blank by rolling it between dies which force the
metal to expand radially into grooves in the die which give the form required for
the threads; the completed screw being indicated by a, Fig. 2. It will be noticed
that the diameter of the threaded portion t is substantially the same as the diameter
of the enlarged plain portion s¹ of the shank at its junction with the head h, as
indicated by the parallel dotted lines c. The screw-threads terminate practically
about midway of the point portion p, or at the intersection of the parts p² and p³,
in oppositely arranged sharpened edges t¹. See Figs. 2 and 3. These sharpened or
chisel-shaped edges are first to enter the wood (after the introduction of the spur p¹),
and readily cut their way through it as the screw is advanced (see arrow direction)
by the aid of the driver.
The full efficiency or holding capacity of the screw a is thus obtained, it being
well known that a screw threaded to the extreme end of a cone-shaped point adds
nothing to its holding powers.
It is obvious that the sharpened or spur-shaped tip p¹ may have a pyramidal form,
substantially as represented by Figs. 5, 6 and 7, in lieu of the conical form shown
by the other figures, without departing from the spirit of the invention. In such
case the blanks, Fig. 5, are cut off by means of dies having a correspondingly shaped
cavity.
I would further state that if the point be extended as indicated by dotted lines in
Fig. 1, then the point p would be too blunt to serve one of the purposes required, or
in other words, the resistance to entering the wood would be too great, whereas the
spur-point portion p¹ serves to overcome the objections by having a more acute angle.
Another advantage of the double-angle formed on the point portion of the blank, see
Fig. 1, is that the part p² having a less acute angle is essential in order to provide
the amount of metal necessary to be transformed into the enlarged threads on the
point as compared with an ordinary rolled wood screw having a screw-threaded point.
That is to say, if the sides of the point formed a true cone, then the metal taken to
produce the thread would leave the contiguous sides more acute than the entering end,
which is un desirable. Practically, by first making the sides of the point p of the
blank substantially as represented in Fig. 1, the root of the thread when formed

page_text: thereon will then be substantially a continuation of the sides forming the entering
portion p'. See Fig. 2. By means of such construction it will be observed that a
reentrant angle is formed in the blank at the intersection of the two parts p², p¹,
forming the point portion, which angle practically disappears when the thread is
produced. See Fig. 2.
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
1 claim is :-
1. A screw with the threads of the cylindrical portion extended on to the
conical surface of the point, but reduced in diameter to correspond with the diameter
of such surface, and terminating in a cutting edge before the extreme point is
reached.
2. A wood screw having the threads of the cylindrical portion extended on to the
surface of the point portion, but reduced in diameter to correspond with the diameter
of such surface, and terminating in a cutting edge, and having an unthreaded spur-
shaped entering portion p', substantially as hereinbefore described.
Dated the 21st day of October 1890.
PHILIP M. JUSTICE,
55 & 56, Chancery Lane, London, Agent for the Applicant.