Improvements in Dies for Rolling Wood Screws.
Year: 1890

page_text: Date of Application, 11th Nov., 1890-Accepted, 13th Dec.. 1890
COMPLETE SPECIFICATION.
Improvements in Dies for Rolling 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 be performed, to be particularly
described and ascertained in and by the following statement. :-
;
In the manufacture of rolled wood screws, that is, screws having the thread raised
from the body of the blank by compression and by rolling between dies provided with
a series of oblique grooves, into which the metal is forced by the ribs between the
grooves, it has been the usual practice to employ dies whose working faces are provided
with parallel inclined grooves and ribs which have a gradually varying arca cross-
sectionally in other words, the ribs at the entering or front end of the die are
made V-shape or narrow so as to enter the blank more easily; from this point the
ribs extend toward the rear or
the area of the ribs gradually increasing correspondingly. I am aware that some
finishing end in a gradually changing form and size,
of the first dies employed in rolling threads on the body of the screw-blank had a
uniform size and shape throughout their length; in such case there could be no
gradual development of the thread; in fact, such dies were used to produce the threads
of "machine-screws," that is, screws having comparatively shallow V-shape threads
of fine pitch, the metal thus transformed being in a longitudinal direction, rather
than radial.
An objection to the use of dies provided with gradually varying ribs and grooves
employed to raise the metal radially from the blank's surface, particularly when used
to produce the threads of gimlet-pointed wood screws, is that the blank in its passage
between a suitably mounted and operating pair of such dies is liable to become more
or less changed from its proper position or true relation to the dies, the product then
being imperfect. It is well known that it is extremely difficult to so accurately adjust
a pair of dies that the blank will "track" properly with the grooves and ribs at all
points of the die; consequently any material variation in the dies, or even in
introducing the blanks to them at the proper instant, will cause the blanks to issue at
the end of the operation as imperfect, if not wholly worthless screws.
stated, if gimlet-pointed screws are to be produced, a slight variation of the blank
As before
from its true relation, vertically, either up or down, will from this cause alone be
ufficient to discard the product; that is, if the blank rises and is not immediately
orrected, the screw thus produced will not have a full thread on its point portion; on
he other hand, if the blank moves in the opposite direction, or downwardly, there
vill be an excess of metal to be provided for, which results in clogging the dies, &c.
The object I seek to accomplish by my present improvement is to provide thread-
orming dies with grooves and ribs so constructed and arranged that the objections
efore referred to are practically overcome.
ssentially of a die having its working face provided with a series of inclined parallel
To that end, my invention consists
rooves and ribs which are arranged in the form of two or more steps or terraces;
at is, suppose the face of the die is formed longitudinally, say in four rectangular
ections, in the first section, or entering portion, the several ribs are alike and
iform in cross-section throughout; in the next section the ribs are also alike, but
ider than the first-named section; the ribs of the third section are also uniform,
t wider than those of the second; and the ribs of the last or finishing section
ing still wider, but uniform throughout this portion of the die; the said rectangular
ctions being connected by quite short sections having beveled or curved edges.
By reason of my improvement I find that in case the axis of the blank is not at
actly right angles with the plane of movement of the die, the tendency of the ribs
ID 77

page_text: at the junction or intersection of any of the stepped sections is to slightly retard
the blank at the adjacent junction until the corresponding portion of the opposite
die corrects such variation in the blank's position, when the continued action of the
dies completes the screw and drops it from them.
In the appended sheet of drawings, Figure 1 represents a side elevation of a thread-
rolling die having its working face provided with a series of stepped ribs and grooves
embodying my invention, the shaded portions indicating the ribs. Figs. 2, 3, 4, 5 are
cross-sectional views of the die, taken on lines a a, b b, c c, d d, respectively, of Fig. 1,
the angle of the sides of the ribs transversely being the same throughout; Figs. 6,
7, 8, 9 are similarly taken sectional views, the angle of the sides of the ribs being
variable; and Fig. 10 shows in detail, although somewhat enlarged or exaggerated,
a face or front view of one of the ribs of my improved die, the die in this case having
seven sections or steps.
In the drawings, A indicates my improved die as a whole. As represented, it is
adapted to be used as a reciprocating die, although the improvement may be equally
applicable to a curved or cylindrical-shaped die. The lower portion p extends above
or in front of the general surface of the die for the purpose of forming threads on the
point portion of the screw-blanks, as in making gimlet-pointed wood screws;
obviously this raised portion 2 may be omitted without departing from the invention.
indicates my improved form of ribs, and g the grooves between the ribs.
These ribs are made as thin and sharp as possible (consistent with the strength and
quality of the metal employed) at the front portion of the entering end, so as to be
more easily impressed into the screw-blank at the commencement of the thread-
forming operation. Figs. 2 and 6 represent cross-sectionally two forms of ribs, taken
on line a a of Fig. 1, well adapted for dies of this character. The said ribs and
grooves are arranged parallel with each other and extend obliquely across the face of
the die. As represented in Fig. 1, the face of the die is formed longitudinally into
four substantially equal rectangular sections; see s, s1, 52, 53, at the bottom of the
die. In these sections or divisions the form of the ribs and grooves transversely
throughout any individual section is alike or uniform, but the ribs change or vary in
width or thickness at each section; or in other words, each individual rib r is also
formed of a series of rectangular-shaped sections, as indicated by s, s', s², &c. At the
junction or intersections of the several rectangular sections of the rib, the face of
the rib at its opposite edges has the form of a truncated cone, or it may be curved at
such points in lieu of such truncated or beveled edges. In the last or finishing
division (as s, Fig. 1, or so, Fig. 10), the ribs are quite wide, while the grooves are
correspondingly narrow; in fact, the form of the grooves of this section are the
counterpart of the threads to be produced upon the blank; see Figs. 5 and 9.
In Fig. 10, I have indicated a single rib r, somewhat exaggerated, having seven
divisions, viz.: s, s', $², s³, s¹, s², so. The number of divisions used may be increased
or diminished without departing from my invention, the essential feature of which is a
die provided with a series of ribs, each consisting of two or more rectangular
divisions s, s', &c., having different widths, the sides of which throughout the length
of the die, except at the points of intersection t, are parallel with a line drawn through
the centre or axis of the rib.
In rolling screws I prefer to use a pair of straight dies (alike), the same being
reversely arranged and mounted to reciprocate past each other; the screw-blank is
stationary, except the axial motion imparted to it by the action of the dies.
A manner of producing a die having stepped ribs or divisions is as follows: The
die-blank is first properly mounted and secured to a table of a suitable milling or
other machine, over which an arbor carrying a number of milling cutters is mounted
to revolve; these cutters are so shaped and arranged that upon bringing them in
contact with the die-blank, commencing at the rear end and feeding it ahead, the
narrowest portion 3 (as in Fig. 1) of the groove will be cut into the die throughout
its length next, by substituting other cutters adapted to the section and again
feeding the blank ahead, the cutters act to trim away the sides of the grooves, com-
mencing au the back end of the section s²; in a similar manner the sections & and s