An Improvement in Dies for Rolling Screw Threads.
Year: 1890

page_text: Date of Application, 17th June, 1890-Accepted, 19th July, 1890
COMPLETE SPECIFICATION.
An Improvement 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 present invention has relation to dies for forming screw-threads upon screws,
more especially wood screws, by rolling the screw-blanks between them the action
of the latter when properly mounted and operated causing the metal to raise radially
from the body of the blank to form the threads.
The invention herein described and claimed is an improvement upon the die patented
to me September 20, 1887, under No. 12,730 of 1887 (in Great Britain). In that
die the series of inclined grooves and ribs were made parallel to each other, the
obliquity of the ribs and also the angle of the sides thereof being constant from ono
end to the other. The action of such former dies was to force the ribs into the
screw-blank to the required maximum depth at the commencement of the operation,
thereby limiting the pressure towards the axis to a comparatively small degree; the
continued movement of the dies caused the metal between the ribs to be more
and more compressed laterally and at the same time radially expanded into the
grooves of the dies until, at the end of the operation, it fills them, the threads
then being homogeneous or solid and a counterpart of the grooves at the end of
the dies.
As the metal between the ribs expands radially during the progress of the rolling,
the diameter of the blank measured across the threads increases and by reason of this
increase of the diameter a longer portion of the dies is required as the rolling
progresses to give a complete revolution to the blank, and inasmuch as the distance
between the central line of the threads of a screw is constant, and consequently the
distance between the central line of the ribs of the dies is constant, it is necessary,
when the length of the die required for one revolution of the blank is increased, that
the angle of the ribs of the die with its line of motion should be reduced. Unless
this is done there is a tendency to move the blank across the dies, and in the ordinary
way of arranging the dies to raise the conical point of the blank away from the
inclined portions of the faces of the dies which form the point of the screw and
produce an imperfect thread. An unnecessary strain is also brought upon the dies
which sometimes results in breaking them.
1 have found that I can remedy these difficulties by changing the pitch or
inclination of the ribs and grooves of the dies to correspond with the increasing
diameter of the blank as the rolling progresses. Theoretically this change of the
inclination should be constant so that the ribs would present curves, but for practical
purposes it is sufficient and much easier to make the dies in sections with a different
inclination of the rihs corresponding to the increase of the diameter of the blanks.
A revolution of the blank does not correspond precisely with the circumference of the
edges of the threads at different stages of the rolling but to a circumference inter
mediate between that and the circumference of the bottom of the groove.
My improved die is represented in the annexed five sheets of drawings, in which
Figure 1, sheet 1, shows a front view of the working face of a die having straight
inclined parallel ribs and grooves, the inclination being constant from one end to the
other; Fig. 2 is a similar view showing one example of my improved die. As drawn
the die is formed of four pieces or sections, the obliquity or inclination of the ribs and
grooves of one section varying somewhat from those of the adjoining section, as may
be readily determined by placing the drawing horizontally in front of the eye and
nearly level therewith, and ranging across the Figure.

page_text: Fig. 3, sheet 2, is another example of my improved die. In this drawing, however,
the ribs and grooves have a curved form, the angle of which with the line of move-
ment of the die is constantly varying, the entire die being in one piece. Fig. 4 is a
top or edge view showing successive grooves along the edge and the increasing
distance between them measured lengthwise and the increasing width of the top of
the ribs. Fig. 5 is à longitudinal sectional view taken through the bottom of one of
the grooves. Fig. 6 represents a die the same as shown in Fig. 3, except that it is
in four pieces or sections. Fig. 7 is a diagram, introduced to show graphically by
comparison the difference between the former method of arranging the ribs and my
improved way of disposing them.
Fig. 8, sheet. 3, shows in elevation a piece of a screw-blank, greatly enlarged, before
being subjected to the action of a pair of screw-threading dies. Fig. 9 represents the
same, in section, during the screw-threading operation, the ribs of the dies being
impressed into the metal to the required full depth and corresponding say to a
section taken through the blank and the dies at the end of the first half-revolution of
the blank, when both dies are made to reciprocate. Figs. 10, 11, 12, 13 and 14
represent similar sectional views showing the progressive development of the screw-
threads, and the increase of diameter. Fig. 15, sheet 5, shows sectionally the fully
developed screw-thread resting in the dies at the end of the operation. Fig. 16 is a
view of the front end of a die, in reduced scale, adapted to roll a gimlet-pointed
wood screw. Fig. 17 represents the opposite end of the die. Fig. 18 shows in cross-
section, a pair of such dies at the completion of the screw-threading operation, having
a screw retained between them, and Fig. 19 is an enlarged sectional view of a rolled-
thread wood screw, cut through its longitudinal axis.
ር
In the several Figures, the parts marked indicate the ribs or bars of the dies,
and the grooves between the ribs. A designates my improved die, that is, a die
having the inclination or obliquity of the ribs and grooves variable or changing from
one end of the die to the other, while A' Fig. 1, indicates a die having straight
inclined grooves and ribs, substantially as common to former construction of dies,
wherein the amount or degree of inclination of the ribs is uniform from one end of
the dies to the other end. I would state that the several dies represented in sheets 1
and 2 of the drawings, as drawn, would roll the screw-thread only on the straight
or cylindrical part of a rod, or blank; the face of the ribs of the die transversely
being flat. In order to produce gimlet-pointed screws a, see sheet 5 of the drawings,
the general contour of the face of the dies transversely would be modified accordingly,
as indicated in Figs. 16, 17 and 18, at the upper and lower edges of the dies, wherein
the ribs and grooves are adapted to produce upon the point portion of the
blank a screw-thread e' (Fig. 19) having a constantly diminishing depth towards the
point. In the drawing I have represented, cross-sectionally, what I consider to be
the best form for the grooves and ribs; the face of the ribs is thin and slightly
truncated at the entering or front end where the rolling commences, and much wider
at the opposite end; the angle of the two sides of the ribs being alike and constant
from one end to the other, as stated in the Specification to the Letters Patent before
referred to. In forming the threads of a screw by means of a pair of these dies the
thin end of the ribs are forced directly into the metal of the body b of a blank at the
commencement of the operation to the maximum depth required, and as the rolling
progresses the metal is more and more compressed between the ribs and gradually
expands into the grooves of the dies until at the end of the operation, it fills them and
the thread is completed.
A manner of forming the grooves g of the dies A¹, shown in Fig. 1, is to place the
steel blank (annealed) upon the table of a suitable milling machine and then block it
up to the desired angle and secure it in place; the machine is further provided with a
revolving arbor carrying a milling tool or cutter, or a series of cutters, having
transversely the counterpart of the grooves to be produced; now upon feeding the
table ahead slowly the revolving cutters will cut away the blank and form ribs r,
angle of its sides being constant from one end of the die to the other. The die after
being hardened is then ready for use. The die shown in the other Figures may be
the

page_text: cut in a similar manner to that just described except that a cam or former may be
employed to give an endwise movement to the revolving cutting arbor corresponding
to the varying obliquity or inclination of the grooves and ribs coincident with the
travel of the table.
By referring to the diagram represented in Fig. 7, the light diagonal line m'
indicates say the centre of a rib, or groove, of a die, the inclination being constant
from its commencement to the end of the die, substantially as common to dies formerly
made. In said Fig. 7 the vertical distance between the horizontal lines indicates
the corresponding or axial distance between the screw-threads produced by a pair of
suitably operated dies. It will be seen that as the inclination of the ribs m¹ is constant
the horizontal divisions being alike, the several intersections of the lines n and m¹ will
be equi-distant, therefore the horizontal distance between the corresponding
ordinates 1, 2, 3, &c. along the upper edge of the Figure are also equal. But as
the metal of the blank between the ribs is continuously rising during the process of
forming the screw-threads it follows, as before stated, that each succeeding revolution
of the blank on its axis should travel an increased distance, this increase I have
endeavoured to indicate by the heavy line m which corresponds relatively with the
line m' just described. The curved line m where it intersects the lines n it will be
seen cuts it at unequal points; the resulting series of ordinate 1, 2, 3 &c. being
indicated at the lower edge of the figure. Assuming now that the horizontal distance
along the die from the commencement "0" to the first ordinate "1" represents say
one-half the circumference of the blank at the root of the screw-thread, the successive
bottom ordinates 2, 3, 4, 5, 6 and 7 indicate the correspondingly increasing circum-
ference of the screw due to the gradual development of the thread, the length of the
divisions gradually increasing in a corresponding ratio, although the diameter 6' of
the screw at the bottom of the thread remains practically the same throughout the
operation, as represented by Figs. 9 to 15. It will be seen that an ordinary die as
shown in Fig. 1, and as indicated by line m¹, Fig. 7, is made considerably shorter than
my present improved die, notwithstanding the number of divisions or revolutions of
the blank is the same in both cases.
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 die for rolling screws by expanding the metal axially to form threads, provided
with ribs and grooves the acute angle of which with the line of movement of the die
diminishes continually or by sections towards the finishing end of the die to correspond
with the increasing diameter of the threads of the screw.
Dated the 15th day of May 1890.