An Improved Method and Means of Forming Screw Threads on Rods and the like.
Year: 1894

page_text: Date of Application, 30th Oct., 1991-Accepted, 1st Dec., 1894
COMPLETE SPECIFICATION.
An Improved Method and Means of Forming Screw Threads on Rods
and the like.
I, SAMUEL PAUL LEHMANN, Engineer, of South Villas, Camden Square, in the
County of London, do hereby declare the nature of the said invention and in what
in inner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
This invention relates to an improved method of forming screw threads on rods,
tap-bolts and the like, and to the means to be used in carrying such improved
method into effect.
The improved method consists essentially in rolling the screw threads into the
substance of the rod by the agency of rotating formers constructed and arranged
to co-operate in manner hereinafter described, without removing any of the
substance of the rod, as distinguished from the present method of cutting the screw
threads in the substance of the rod by removing a portion thereof by stocks and
dies or screw-plates.
Such present methods are disadvantageous, in that they cause a considerable
waste of the material of the rod correspondingly reducing its strength, and in that
they are liable to form the screw-thread with a relatively jagged or rough edge
caused by the cutting and dragging asunder of the particles of metal of the rod in
the formation of the screw thread and so to form the screw thread of a weakened
substance comparatively liable to be stripped off if subject to any considerable
strain, and in that they require a constant supply of lubricant to the cutting tool to
facilitate the operation thereof.
The improved method remedies or avoids these disadvantages and tends to
consolidate the peripheral parts of the rod in which the screw-thread is formed and to
produce a rolled screw-thread of a smooth and even formation and of a consolidated
substance much less liable to strip off than a screw-thread formed by a cutting
operation.
The accompanying drawings illustrate two tools adapted with rotatable forming
rollers constructed and arranged as hereinafter more particularly described.
Figs. 1 to 5, illustrate an arrangement in which the formers occupy a fixed
relation to each other, and
Figs. 6 and 7, illustrate an arrangement in which one of the formers is adjustable
in relation to the other two which occupy a fixed relation to each other.
Fig. 1, is a plan; Fig. 2, a side elevation; and Figs. 3 to 5, sections respectively
on the lines 1-1, 2-2, 3-3, Fig. 1.
Fig. 6, is a plan; and Fig. 7, a section on the line 4-4, Fig. 6.
a, represents the revolving formers, the periphery of each of which is formed
with ribs a', of the shape of the screw-thread desired to be formed, each of said
ribs being continuous around the periphery of its former and in a plane at right
angles to the axis thereof, and the series of such ribs of each former being in
planes parallel to each other and distanced apart equal to the pitch of the screw-
thread desired to be formed.
A series of such formers is arranged in concentric relation to an aperture 6', in a
holder or tool b, through which the rod c, on which the screw-thread is to be
formed, is passed. The formers will, thus, also be concentric about the rod, and,
being arranged equidistant from each other, they will be adapted to act on the rod
simultaneously at different parts of its periphery equidistant from each other.
50

page_text: Each of the series of such formers is also so arranged as to cause its parallel
ribs to occupy an angular relation to the axis of the rod in agreement with the
helical angularity of the screw-thread to be formed therein, the formers being
located by and adapted to freely rotate about studs d, which are inserted into
stud holes 62, in the tool or holder b, each in such an angular position as will cause
its former a, to present its parallel ribs a¹, in the desired angular relation to the
axis of the rod to produce a screw-thread of the desired helical angularity.
Moreover, the series of such formers a, are so arranged in successive relation to
each other that the innermost or acting surfaces of the forming ribs a¹, of each
thereof will be in the proper pitch-relation to the one immediately preceding it, so
that the series of formers will co-act to produce the desired screw thread simply
upon the introduction of the rod c, between their innermost or acting surfaces and
turning either the rod about its axis between the series of rotating formers, or
turning the tool holding the series of rotating formers about the axis of the rod,
the result being alike in both cases in producing an end wise motion of the rod
relatively to the rotating formers and the rolling of the screw-thread into the
periphery of the rod.
To facilitate the introduction of the rod c, between the formers a, I may chamfer
off part of the circular periphery of the topmost rib a', of one thereof, as at a
(Fig. 1) retaining, however, the forming edge in the same plane wholly around the
former, which allows the end of the rod to sink a little when it engages with the
top-most ribs of the other formers, and causes it to be caught between all
the formers as the full periphery of the chamfered rib comes into engagement
with it.
Fig. 6, represents an arrangement wherein one of the formers a, (held by a
pivotted arm 63,) is adjustable relatively to the others (held by an arm b*,) which
occupy a relatively fixed position, which arrangement facilitates the insertion of
the end of the rod between the formers by opening the arms 63, 6, as represented, and
then closing the arms together so as to bring the adjustable former into its proper
relation to the other formers so as to grip the inserted rod between the series.
A spring e, tends to separate the arms 63, 64, and a spring lever f, and cam 6º,
retain the arms when they have been closed together.
9, represents adjusting screws which permit of a slight adjustment of one of the
formers relative to the others thereof,
In the formation of a screw thread on a rod by the said improved means, the
material of the peripheral part of the rod in which the screw-thread is formed is
compressed, by the penetration thereinto of the adjacent ribs of each former, into
the space between such ribs, and is shaped and rolled and consolidated thereby into
a truly helical screw of equal pitch throughout.
The diameter of the core of the produced screw is determined by the diameter
of the ribs of the former, and is thus somewhat less than that of the rod, while
the external diameter of such screw is determined by the core diameter of the
formers, and somewhat exceeds that of the rod. If it is required that the diameter
of the screw should be identical with that of the rod, a sufficient turning is first
taken off that part of the rod on which the screw is to be produced.
6 is a gauge hole for the rod on which the screw is to be produced, and 67 is a
gauge hole for the produced screw.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is,
1. The hereinbefore described improved method of forming screw threads on
rods, tap-bolts and the like; the same consisting in rolling the screw threads into
the substance of the rod without removing any of the substance thereof by the
agency of revolving formers constructed and arranged to co-operate in the manner
described.

page_text: 2. The improved screw forming tool hereinbefore described with reference to
Figs. 1 to 5, of the accompanying drawings.
3. The improved screw forming tool herein before described with reference to
Figs. 6 and 7, of the accompanying drawings.
Dated this 26th day of October 1894.
DAY, DAVIES & HUNT,
321, High Holborn, London, W.C., Agents for the Applicant.