Improvements in Dies for Rolling Screw Threads.
Year: 1891

page_text: e of Application, 20th Oct., 1891-Accepted, 28th Nov., 1891
CUMI DETE
Improvements in Dies for Rolling Screw Threads.
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 :-
"
My invention has relation to dies such as are employed in forging (cold) the
screw-threads upon screws by what is termed the "rolling process;" the class of
screws to which the invention more especially appertains being known as "wood-
screws.' Rolled wood screws even though made of the same wire vary greatly in
their holding power according to the form or shape and inclination of the ribs and
grooves of the thread-forming dies; the form of the ribs of such dies transversely
as first employed in thread-swaging was I believe V-shaped, the shape and area of
each rib being uniform throughout its length; the action of such dies upon a screw-
blank is to elongate it, the diameter of the threaded portion being the same as that
of the wire itself, or unthreaded part. I would state that the die just referred to was
employed to produce the threads on small machine screws having fine pitch, such for
example as are used to secure the knobs or handles to the spindles of door-latches.
A later example of thread-rolling machines and dies is that shown in Lake's British
Specification No. 13302 of 1884. In that Specification the ribs of the dies cross-
sectionally are V-shaped at the commencement or entering end but are gradually
transformed into a truncated shape; in operation the ribs are gradually forced into
the screw-blank axially from the commencement to the end, thereby producing a
groove which is gradually deepened and widened, the metal being forced outwardly
from under the ribs of the travelling dies in the form of ridges or threads which
gradually increase in diameter; in that die the angle or inclination of the sides of
the ribs varies throughout its length, that is to say the included angle formed by
the sides of adjacent ribs at the entering end of the die is much greater than
that at the opposite end.
There are still other forms of dies adapted to swaging screw-threads. I have
invented one wherein the inclined ribs and also the grooves thereof transversely are
uniform in shape and area throughout, such dies, however, cannot well produce
screws having the threads raised above the normal surface of the blank to the
extent necessary or essential to wood-screws adapted to be inserted into wood by a
screw-driver, therefore I employ the dies in making what are termed "drive-screws,'
that is, screws having multiple threads and coarse pitch; screws of this class and as
made by my said dies are readily driven into wood by the blows of a hammer and
turn axially while being driven.
In the Specification to British Patent Number 12,730 granted to me Sept. 20th,
1887, I have shown and described "dies for forming the threads upon wood-screws
by rolling the blanks between them and raising the metal to form the thread radially
from the body of the blank without extending the blank lengthwise." In using
the dies the pressure upon the metal towards the axis of the blank is limited to the
commencement of the rolling operation and to a comparatively small part of the
metal displaced." The work of raising the threads is mainly performed by
the inclination of the adjacent or lateral sides of the ribs, such inclination being

page_text: constant from one end of the die to the other. The face of the ribs at the entering
end where the rolling commences is quite narrow in order that they may be required
to displace but little metal; the ribs gradually increase in thickness laterally from
the commencement to the end of the die, the faces thereof being flattened or trun-
cated throughout. A pair of these dies in operation produces a gradually developed
screw-thread, because at each successive revolution of the blank the metal lying
between the constantly varying (in thickness) ribs is more and more compressed
laterally and at the same time gradually expanded radially into the grooves of the
dies until, at the end of the operation, it fills them, and the thread is completed.
The thread cross-sectionally is solid and wedge-shape, being quite thin at its base
or root where it joins the core, and sharp at the point or edge. In these screws the
bottom of the groove being parallel for its whole width with the axis of the screw
the top of the ribs must be flat and the metal of the blank at the bottom of the
groove must be displaced by the ribs of the die to the full width of the groove by a
kind of shearing action at the bottom of the groove.
The present invention is an improvement of the above mentioned die and is
designed to act by a lateral pressure of the metal of the screw blank and its radial
expansion as with the dies just referred to, but by an easier displacement of the
metal with less or none of the shearing action at the bottom of the groove of the
screw as above explained in the use of flat-faced ribs.
I accomplish this object by rounding transversely the top of the ribs of a die for
a part or the whole of their length. The effect of this is to reduce the width of the
inclined sides of the ribs which act upon the metal laterally as the thickness of the
ibs transversely increases and to leave a portion of the metal undisturbed which
would be displaced to form the angle at the bottom by flat-faced ribs, and a groove
rounded at the bottom is produced instead of a flat-bottomed groove forming an
angle with the sides of the threads or ribs of a screw.
In the annexed three sheets of drawings illustrating my present improvements,
Figure 1, Sheet 1, represents a plan of the working face of one die. The lightly
shaded parts indicate the faces of the ribs;
Fig. 2 is a longitudinal sectional view, taken say on line m m of Fig. 1, showing
the ribs constantly decreasing in height;
Fig. 3 is a similar sectional view, the height of the ribs being constant
throughout;
Fig. 4 is a transverse sectional view taken through a pair of the dies, at or near
the finished end, showing a screw, in partial section, between them;
Fig. 5 is a plan view of one of the ribs of the die, detached; one portion of the
rib's face being flat or truncated, the other being rounded as indicated by the
shaded lines;
Fig. 6 is a similar view of a rib, its face being rounded throughout its length;
Figs. 7, 8 and 9 are cross-sectional views of the rib, taken respectively on lines xx,
and 0, of Fig. 5;
20 W,
Fig. 10 is a transverse sectional view, taken on line xx, of Fig. 6 ;
Figs. 11 and 12 are similar sectional views showing modified forms of the ribs;
Fig. 13, Sheet 2, is a longitudinal sectional view, showing my improved die bent
to a circle or curved. in lieu of being straight;
Figs. 14 and 15 are transverse sectional views, showing the form of die-ribs as
Patented by Lake 13302 of 1884 and by Clarke & Harvey U.S. 306132.
Fig. 16 is a plan view of one of the last-named ribs provided with a rounded
face;
Figs. 17 and 18 are cross-sectional views thereof taken respectively on lines xx,
and oo of Fig. 16;
Fig. 19 is a longitudinal sectional view enlarged taken through the centre of a
gimlet-pointed wood screw provided with my improvement;
Fig. 20 is a similar view of the screw, having a double-thread and unthreaded
spur-point ;
Fig. 21, Sheet 3, is a plan view of the working-face of a die embodying my

page_text: improvement. The shaded portions indicate the ribs having rounded faces. The
general arrangement of the ribs being in the form of steps, or terraced, substantially
as represented in British Patent No. 18,155, granted to me Nov. 11th, 1890.
Figs. 22, 23, 24 and 25 are cross-sectional views taken respectively on lines a a,
b b, c c, and d d of Fig. 21;
Fig. 26 is a plan view of a rib enlarged, having a uniform width and -shape
throughout its length, and
Fig. 27 is a transverse sectional view, taken on line ee of Fig. 26, showing the
relation of adjacent ribs to each other.
A in the several figs. indicates my improved die as a whole. The ribs of the die
are designated by a, and the grooves or spaces lying between them by b. The
grooves and ribs at the commencement or entering end of the die are substantially
V-shaped, the angle or inclination of the adjacent sides of the grooves being
practically constant from one end of the die to the other, as represented in Sheet
of the drawings. The height of each rib a may vary throughout as indicated by
Fig. 2, or they may be uniform in height, as in Fig. 3. In any case the width of
the face of the rib varies, being narrowest at the entering end of the die and widest
at the opposite or finishing end. Such width of ribs may vary constantly and
gradually, as shown in Fig. 1, or they may be in the form of a series of increasing
steps, as c, c', c², c³, Fig. 21. The face of the rib at the entering end should be
made as thin or narrow as is consistent with the work imposed upon it. The face
thereof for a portion of its length may be flat or truncated, as at a', Figs. 5 and 7,
such flat portion being joined to a gradually increasing rounded part, see Fig. 5,
the latter terminating in well-rounded ribs, as clearly indicated by Fig. 9, which
represents enlarged a partial cross-section taken on line of Fig. 1, and.also on
line o o of Figs. 5 and 6. The face of the ribs a may be rounded throughout as
shown by Fig. 6 and its sections ra, w to and oo, represented by Figs. 10, 8 and 9,
respectively. Obviously the shape of the grooves 6 gradually changes from the
V-form at the front end, Figs. 7 and 10, to the opposite or finishing end of the die,
where the grooves diverge laterally in curved sides, Figs. 4 and 9, which are the
counterpart of the sides of the screw-threads t, see also Figs. 18 and 25.
In the Clarke & Harvey die before referred to the oblique ribs and grooves are
uniform in height throughout the length of the die, but the angle or inclination of
the sides thereof constantly varies, as indicated by Figs. 14 and 15; the former fig.
shows enlarged, cross sectionally, a portion of the die at the entering end and the
latter a similar fig. taken at the opposite or finishing end. The rib a is V-shape
at the front, its face being sharp and gradually widening therefrom to the other
end, see a³,. Fig. 15, thereby gradually changing the angle of its sides until a sharp
V-shape groove is produced (Fig. 15) which is a counter part of the thread. The
ribs and grooves of such a die may be rounded, as indicated by Figs. 16, 17 and 18;
the latter then representing ribs & and grooves 6 substantially like those shown by
Figs. 4, 9 and 25. Although dies having ribs and grooves, as shown by said
Figs. 16, 17 and 18, may be employed to swage or roll the threads of screws, I
preferably use dies having the angle or inclination of the sides of the ribs a sub-
stantially constant from one end of the die to the other, Figs. 1 to 10, because the
threads thus produced are more gradually developed and more homogeneous, the
per centage of loss is less and the work is accomplished with less power.
The die A may be secured to a revolving cylinder or carrier m Fig. 13, the
operation of rolling the screws then (if combined with a stationary die) being sub-
stantially as set forth in the Specification of the said Clarke & Harvey hereinbefore
referred to.
In Figs. 11 and 12 the bottom of the ribs a are rounded as well as the faces, the
last or finishing section however would be substantially as represented by Fig..9.
An advantage resulting from thus filleting the root of the ribs for a portion of their
length is that it increases their strength in a lateral direction.
Aldie provided with ribs a', Figs. 26 and 27, having a uniform width and area
transversely throughout their length may be employed, but the ribs cannot produce

page_text: a gradually developed screw-thread as compared with my improved die provided
with developing ribs a, because the grooves (Fig. 27) themselves are uniform
throughout.
s indicates my improved wood-screw, the threads t thereof being produced by
rolling, by means of the dies A hereinbefore described. The shank or unthreaded
portion of the screws I make slightly tapering or conical, this is performed in
the dies simultaneously with the operation of upsetting the metal therein to form
the heads h; practically I prefer that the diameter of the shank at its intersection
with the head shall be substantially the same as the diameter of the threaded
portion. The threads are filleted at the bottom t¹ thus adding to their strength
in a lateral direction. The screws may be gimlet-pointed, as at p Fig. 19, or the
point-thread may be wholly, or in part, omitted, thereby producing a spur-point p¹,
Fig. 20.
The ribs a and grooves b of my improved die A may be cut by a revolving
milling-tool, or a series of them, having the proper form to give the required
inclination or bevel to the sides of the ribs. The die-blank is first elevated at one
end and secured to a reciprocating table or carriage in such a manner that its longi-
tudinal axis in a horizontal plane is not parallel with that of the moving table,
which latter carries the blank past and in contact with the tool; the rounded form
given to the face of the ribs may be done simultaneously with the cutting of the
grooves, but practically I prefer to first truncate them by the tool just referred to
after which the rib's faces are rounded off by another cutter or cutters or by other
suitable means. The dies are subsequently hardened thereby rendering them ready
for use.
The action of the dies in forming the filleted threads t, t', of a screw may be
described as follows:-Let it be assumed that a pair of the dies A, with the ends
reversed, are arranged to move back and forth past each other in a suitable
machine, or substantially as shown and set forth in the Specification to British
Patent No. 12,717 granted to me Sept. 4th, 1888. To roll a screw, the blank is
introduced vertically between the ends of the separated dies (the latter then being
at the end of the stroke or on the "dead centre") which immediately seize it from
opposite sides, the blank is rolled axially by the action of the two travelling dies
until they pass each other, when it drops from them completely threaded. At the
commencement of the operation the narrow ends n of the ribs a of the dies are
forced into the metal to the maximum depth required, the lateral separation of the
working faces of the opposite dies being constant throughout and corresponding to
the diameter of the root or core of the screw; as the rolling progresses the metal
seized between each pair of the ribs above the curved portion of the ribs is com-
pressed and at the same time gradually expanded into the grooves 6 of the dies
until, at the end of the operation, it fills them, and the thread t, t, is completed, the
threaded portion then being substantially as represented by Figs. 4, 19 and 20.
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 die for raising the threads of a rolled screw radially from a screw-blank by
compressing the metal for the thread laterally between the converging sides of the
ribs of the die and having the faces of the ribs rounded to form a concave bottom
of the grooves of a screw; said ribs being narrow at the end where they commence
to form the thread, so that they may be forced at the commencement of their action
into the metal to the depth required to form the body of the screw, and increasing
in width act laterally upon the metal between the ribs and force it into the
grooves which at the end of the operation give it the precise form required for the
thread.
2. The die A, substantially as herein before described, for raising the threads of
a rolled screw radially from a screw-blank; the working surface of the die being
provided with a series of obliquely arranged expanding or developing ribs a having

page_text: rounded faces and converging adjacent sides, each rib being narrow at the end
where it commences to form the thread and increasing in width transversely to the
opposite end of the die.
Deted the 2nd dex of October 1891
CHARLES DAKE ROGERS,
Inventor.