Improvements in Screws.
Year: 1889

page_text: COMPLETE SPECIFICATION.
Improvements in 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
particularly described and ascertained in and by the following statement :-
In wood screws and in many other kinds of screws the bottom of the grooves
between the threads is a spiral cylindrical surface which, if developed into a plane,
would be flat. This surface, the area of which is often more than half the area of
the cylinder from which the screw is formed, contributes nothing to the holding
capacity of the screw, except by its friction upon the corresponding plane surface of
the wood or nut in which it is inserted.
With a screw of a given diameter and a thread of a given shape and size, the
pitch of the tread depends upon the width of the groove, and an increase in the
width of the groove increases the surface, which is comparatively inefficient in the
holding capacity of the screw. My improvement makes the bottom of the groove
efficient in its hold upon the wood or nut in which it is inserted. This I do by
giving different diameters to different parts of the bottom of a groove so as to form
surfaces inclined to the axis of a screw and produce surfaces which will resist a
longitudinal strain upon the screw. Such surfaces may be regarded as minor threads
or ribs and grooves auxiliary to the larger threads or ribs, which engage more
deeply with the wood or nut.
In the drawings hereto annexed, one form of my improved screw is represented in
Fig. 1, in which a rectangular rib is formed at the bottom of a wide groove between
the principal threads. Fig. 2 is a longitudinal section of the lower part of the screw
represented in Fig. 1. Fig. 3 is a similar section of a screw with the threads
extending to the point. Figs. 4 and 5 represent different forms which may be given
to the bottom of a groove. Figs. 6, 7 and 8 show different forms which may be
given to the point of a screw.
b
In all the figures a represents the principal thread or rib of a common form, and
in Figures 1, 2 and 3, 6 represents a rectangular thread or rib at the bottom of the
groove between the principal threads. In Fig. 4 c represents an angular rib at the
bottom of the groove, and in Fig. 5 d represents a curved convex rib. It is obvious
that, while these low projecting surfaces might not of themselves be efficient for the
introduction of the screw into wood or a nut, they add materially to its capacity to
resist a longitudinal strain.
The bottom of a groove might be formed of a number of the common V-shaped
or rectangular grooves and threads or ribs of low elevation. All these forms may be
produced by cutting away the metal in the ordinary way or by rolling in the manner
described in a U.S. patent granted to me Sept. 20, 1887, No. 370,354.
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 :-
1. A screw having the bottom of the grooves between the threads formed into low
auxiliary ribs or projecting surfaces, which engage with the wood or nut into which it
is inserted and increase its holding canacity.

page_text: 2. A rolled screw having the diameter of the threaded portion exceeding that of
the plain or unthreaded portion, and having the bottom of the grooves between the
said threads formed into low auxiliary ribs or projecting surfaces, the outer faces of
which have substantially the same diameter as the said unthreaded portion.
Dated this 20th day of August 1889.
CHARLES DAKE ROGERS,
Inventor.