Improvements in Screw Cutting Apparatus.
Year: 1891

page_text: Date of Application, 17th Nov., 1891
Complete Specification Left, 12th Aug., 1892-Accepted, 22nd Oct., 1892
PROVISIONAL SPECIFICATION.
Improvements in Screw Cutting Apparatus.
I, THOMAS ALEXANDER BOYD, of the Shettleston Iron Works, Shettleston in
the County of Lanark, North Britain, Engineer, do hereby declare the nature of
this invention to be as follows, that is to say:-
My said invention has for its object the cutting of screw threads on bolts, pins,
spindles, shafts, rods, tubes, and the like, in an improved, expeditious, and
economical manner.
In carrying out my invention I employ a rotating milling cutter, which is by
preference made as hereinafter described, and to which I present the bolt or other
article, upon which the screw thread is to be cut, in an inclined position, the said
article being at the same time made to rotate slowly and with a screwing motion
corresponding to the pitch of the screw thread to be cut.
The milling cutter is made with several circular rows of cutting teeth and
operates simultaneously on the parts between several convolutions of the intended
thread, so that for each complete turn of the bolt or other article operated on, a
length of thread is formed corresponding to the number of circular rows of
cutting teeth.
For the purpose of forming the milling cutter in an accurate manner, I prefer
to first form on a primary piece of ground steel a screw thread having a number
of convolutions corresponding to the number of circular rows of teeth of the
intended milling cutter, this being done by means of an accurate screw-cutting
lathe operating in the ordinary way. A gap or groove is cut across the threads of
the primary cutter, and the severed or cut ends of the thread are applied as
cutters to form the milling cutter. The gap or groove is cut with an inclination
to the axis of the primary cutter and so as to be at right angles to the screw
threads;
and this causes the ends of the threads to present a slight convexity,
which produces a corresponding concavity in the milling cutter. This concavity
of the milling cutter is necessary because of the inclination of the bolt or article
operated on, and as otherwise the milling cutter would cut more deeply at its
middle part than at the ends.
The bolt or article to be operated on is held in a chuck at the end of a tube
carried in a pair of bearings, between which there is on the tube a wheel
connected by suitable gearing with the driving mechanism of the milling cutter.
The wheel turns the tube by means of a longitudinal groove and a key, and a part
of the tube is screwed externally to work in an internally screwed boss or tube
having on it a handwheel. Whilst an operation is in progress the internally
screwed boss or tube is fixed and the rotation of the inner tube makes it screw
forwards so as to give the bolt or other article the proper movement; but
afterwards it is unfixed and then the hand wheel is turned quickly to move the
inner tube backwards.
The parts of the improved apparatus can be adjusted or shaped so as to form
screw threads on tapered or curved articles.
Dated this Sixteenth day of November 1891.
EDMUND HUNI,
Applicant's Agent.

page_text: COMPLETE SPECIFICATION.
Improvements in Screw Cutting Apparatus.
I, THOMAS ALEXANDER BOYD of the Shettleston Iron Works, Shettleston, in
the County of Lanark, North Britain do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement :-
My said invention has for its object the cutting of screw threads on bolts, pins,
spindles, shafts, rods, tubes & the like & also internal screws in an improved
expeditious & economical manner. A sheet of explanatory drawings is hereunto
appended to be hereafter referred to in describing my invention.
Fig. 1 shews the end of an ordinary milling machine spindle carrying a rotating
milling cutter hereafter fully described & which is the main feature of my
invention & an apparatus for holding & giving the required movements to the
bolt or other article upon which the screw thread has to be cut.
Figs. II & III shew (full size) the rotating milling cutter.
Figs. IV & V shew (also full size) a primary cutter hereafter described with
which I prefer to form the rotating milling cutter shewn in Figs. II & III.'
In carrying out my invention I employ a rotating milling cutter as shewn No. 1,
Fig. 1 and in Figs. II & III on annexed sheet of drawings which is by preference
made as hereinafter described & to which I present the bolt 2 Fig. 1 or other article
upon which the screw thread is to be cut in an inclined 'position, the said 'article'
being at the same time made to rotate slowly & with a screwing.motion corresponding
to the pitch of the screw thread to be cut.
The milling cutter is made with several circular rows of cutting teeth &
operates simultaneously on the parts between several convolutions of the intended
thread so that for each complete turn of the bolt or other article operated on a
length of thread is formed corresponding to the number of circular rows' of
cutting teeth.
For the purpose of forming the milling cutter in an accurate manner I prefer to
first form on a primary piece of round steel (Figs. IV & V) a screw thread having
a number of convolutions corresponding to the number of circular rows of teeth of
the intended milling cutter this being done by means of an accurate screw cutting
lathe operating in the ordinary way. A
across the threads of the primary cutter & the severed or cut ends of the thread
gap or groove (11 Figs. IV' & V) is cut
are applied as cutters to form the milling cutter 1 Fig. 1 & Figs. II & III. The
gap or groove 11, Figs. IV & V is cut with an inclination to the axis of the
primary cutter & so as to be at right angles to the screw threads' as shewn by
line 12 Fig. 4 & this causes the ends of the thread to present a slight 'convexity
which produces a corresponding concavity. This concavity of the milling cutter is
necessary because of the inclination of the bolt or article operated on and as
otherwise the milling cutter would cut more deeply at its middle part than at the
ends..
1
The bolt or article to be operated on is held in a chuck 3 Fig. 1 at the end
of a tube 4 Fig. 1 carried in a pair of bearings 5 Fig. 1 between which there is
on the tube a wheel 6 connected by suitable gearing with the driving mechanism of
the milling cutter. The wheel 6 turns the tube 4 by means of a longitudinal.
groove & a key, & the tube 4 carries a virrel 7 which is screwed externally 4
same pitch of thread as is to be cut on the bolt 2 to work in an internally screwed
boss or tube 8 Fig. 1 having on it a hand wheel 10 Fig. 1.
Whilst an operation is in progress the internally screwed boss or tube 8, Fig. 1
is fixed by means of a set screw 9, Fig. 1 & the rotating of the inner tube 4
makes it screw forwards so as to give the bolt or other article the proper
movement; but afterwards it is unfixed & then the hand wheel 10 is turned
quickly to move the inner tube 4 backwards. The bearings 5. 5 are carried upon

page_text: a cross slide which is used to feed the bolt 2 Fig. 1 on to the cutter 1 Fig. 1 & to
draw it back from same when the screw is formed. The said bearings 5. 5 are
arranged so that they can hold the bolt 1, Fig. 1, in an inclined position suited to
the angle of the thread being cut.
The parts of the improved apparatus can be adjusted or shaped so as to form
screw threads on tapered articles.
Fig. 6 shews two of my improved cutters (Figs. 2 & 3) at work at one time upon
a bolt.
In this case I prefer to arrange the milling machine with two spindles 13 & 14
placed one above & one below the bolt 2, these spindles being arranged so as to
hold the cutters at the required angle in relation to the bolt & so that they can
be set at the required distance apart. They are driven by suitable gearing.
Having now particularly described & ascertained the nature of my said inven-
tion & in what manner the same is to be performed, I declare that what I
claim is
(1) The employment of a rotating cutter having two or more circular rows of
cutting teeth & operating simultaneously on the parts between several convolutions
of the intended thread so that for one complete turn, with the screwing motion
described, of the bolt or other article operated on, a length of thread is formed
corresponding to the number of circular rows of cutting teeth.
(2) The employment of two or more rotating cutters similar to the above
operating at the same time upon one bolt or other article.
T. A. BOYD,
Applicant.