IMPROVEMENTS IN MACHINERY FOR THREADING SCREWS
Year: 1876

page_text: LETTERS PATENT to Thomas Garnett, of Birmingham, in the County of
Warwick, Mechanical Engineer, for the Invention of "IMPROVEMENTS IN
MACHINERY FOR THREADING SCREWS."
Scaled the 27th February 1877, and dated the 11th December 1876.
PROVISIONAL SPECIFICATION left by the said Thomas Garnett at the
Office of the Commissioners of Patents on the 11th December 1876.
THOMAS GARNETT, of Birmingham, in the County of Warwick, Mechanical
Engineer. "IMPROVEMENTS IN MACHINERY FOR THREADING SCREWS."
My said Invention has for its object to effect a more rapid throwing into gear of
those parts of the said machinery by which the traversing motion of the thread
cutting tool is effected.
After the axis carrying the said tool has once performed its traversing motion,
the comb is disengaged from the regulator screw, by which the said axis had been
advanced, and by the action of a spring its return motion is effected. It is now
ready to be advanced again by throwing the comb into gear with the regulator
screw, which is thereby made again to advance the axis carrying the cutting tool.
The time occupied by the parts in making their return motion is lost time, and the
object of my Invention is to reduce this time to a minimum. This I effect in the
following way: The end of the sheft actuating the cutting tool carries a leather
washer, supported by a metal washer. The collar through which the shaft slides is
furnished with a divided bush of a conical figure externally, and situated in a
conical bearing. When the shaft is forced back by the spring, the leather washer
strikes the divided bush, and forcing it into its conical seat, makes it grip the shaft.
The said shaft is thereby brought quickly to rest without any vibratory motion, and
the comb may be quickly brought into gear with the regulator screw without risk
of injury to the machinery.
In order to throw the said comb into and out of gear with the regulator screw I
give the advancing motion to the comb by means of a cam having on it a series of

page_text: rises so shallow as to move the said comb only through a small angle, and thus to
give the required motion to the comb promptly. The return motion of the comb is
produced by a spring.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Garnett in the Great Seal Patent Office on the 5th June
1877.
THOMAS GARNETT, of Birmingham, in the County of Warwick, Mechanical
Engineer. IMPROVEMENTS IN MACHINERY FOR THREADING SCREWS."
My said Invention has for its object to effect a more rapid throwing into gear of
those parts of the said machinery by which the traversing motion of the thread
cutting tool is effected..
After the axis or shaft carrying the said tool has once performed its traversing
motion, the comb is disengaged from the regulator screw, by which the said axis
or shaft had been advanced, and by the action of a spring its return motion is
effected. It is now ready to be advanced again by throwing the comb into gear
with the regulator screw, which is thereby made again to advance the axis or shaft
carrying the cutting tool.
The time occupied by the parts in making their return motion is lost time, and
the object of my Invention is to reduce this time to a minimum. This I effect in
the following way:-The end of the shaft actuating the cutting tool carries a leather
washer, supported by a metal washer. The collar through which the shaft slides is
furnished with a divided bush of a conical figure externally, and situated in a
conical bearing. When the shaft is forced back by the spring, the leather washer
strikes the divided bush, and forcing it into its conical seat, makes it grip the shaft.
The said shaft is thereby brought quickly to rest without any rebound or vibratory
motion, and the comb may be quickly brought into gear with the regulator screw
without risk of injury to the machinery.
In order to throw the said comb into and out of gear with the regulator screw I
give the advancing motion to the comb by means of a cam having on it a series of
rises so shallow as to move the said comb only through a small angle, and thus to
give the required motion to the comb promptly. The return motion of the comb is
produced by a spring.
I will now proceed to describe with reference to the accompanying Drawings the
manner in which my Invention may be performed.
Figure 1 represents in side elevation partly in longitudinal section a screw
threading or worming machine to which my Invention is applied; Figure 2 is a
plan of the same; and Figure 3 is an elevation of the same taken at the left-hand
end of the machine.
Figure 4 represents in longitudinal section drawn to a larger scale the holding
mechanism for preventing the rebound of and vibration in the cutter holder shaft
when the latter makes its return stroke after each cut.
The same letters of reference indicate the same parts in the several Figures of the
Drawing.
A is the frame of the machine; B is the spindle driven in the ordinary way.
From this spindle the several motions of the machine are taken. The said spindle B
is hollow, and has within it the clams by which the blank is held while being
threaded; the blank is marked 2 in the Drawing. C is the cutter holder, which
has a longitudinal or traversing motion given to it, the traverse of the said cutter
holder C being varied according to the length of the screw to be threaded.
The cutter held in the holder C is indicated in dotted lines in Figure 3. The said
cutter holder C is fixed firmly on the cutter holder shaft D, to which shaft D an
advance traversing or longitudinal motion is given by means of the regulator

page_text: screw G on the said shaft D being thrown into gear with the comb or comb holder
nut F, carried by the lever F2 pivotted to the frame of the machine.
When the cutter holder shaft D and cutter holder C have made the required
advance traversing motion to effect one cut of the thread on the blank under opera-
tion, the comb or comb nut F is thrown out of gear with the regulator screw G, and
the return motion of the said cutter holder shaft D and parts carried by it is rapidly
effected by the strong spring L acting on the said shaft. The comb or comb nut F
is now thrown into gear with the regulator screw G, and the cutter holder shaft
makes another advance motion, and the screw is cut a second time, and so on.
The throwing into and out of gear of the comb or comb nut F are effected by the
cam E on the cam shaft H. The said cam E is provided with a series of shallow
rises and depressions, so that the comb or comb nut is moved by the said cam only
through a small angle to throw the comb into gear with or to allow it to be ungeared
from the regulator screw. The lever F2, carrying the comb or comb nut F, is pro-
vided with a stud, which bears upon the cam E. When one of the depressions in
the cam comes opposite the said stud of the comb lever F, the said stud drops into
the said depression (being pressed against the cam by a spring, not shown in the
Drawing), and the comb or comb nut F is consequently drawn back or ungeared
from the regulator screw G, when the return motion of the cutter holder shaft D
takes place by the action of the spring L. When one of the rises of the cam E
comes into action, the comb or comb nut F is again thrown into gear with the
regulator screw G, and the cutter holder shaft D again commences its advance tra-
versing motion.
.
The cam shaft H is driven in the ordinary way by means of gearing at 6³ and H*
from the spindle B.
The cut cam marked I is fixed upon the cam shaft H, which said cut cam I
actuates the rocking cradle J by means of the lever K, as seen in Figure 3. The
cutter holder C rests upon the rocking cradle J, and the motion given to the said
cradle J by the cut cam I determines the depth of the cut of the cutter held in the
cutter holder C. The steps in the cam E agree in time with the steps in the cam I,
so that when the stud of the lever K falls into a space or depression in the cut
cam I, thereby allowing the cutter holder C to fall back from the screw blank at the
same time, the stud on the comb nut lever F2 falls into a space or depression
in the cam E, thereby allowing the cutter holder shaft D, the cutter holder C, and
the regulator screw G, which are acted upon by the spring L, to be returned to their
original positions.
The cutter holder shaft D is so rapidly returned to its normal position by the
spring L that if not prevented the said shaft D and the other parts acted upon by
the spring L would rebound, and time would have to be allowed to let the regulator
screw G come to rest before the comb or comb nut F could fall again into gear with
it. To prevent this rebound I bevil the hole in the cradle J to form a conical seat,
as shown in Figures 1 and 4, and in this conical seat I place a conical split bush M,
through which the cutter holder shaft D slides, and in which it fits accurately. On
the end of the cutter holder shaft D I screw two lock nuts N, and between these
lock nuts and the split bush M I place a leather washer M³, or other soft material,
to prevent noise. When the cutter holder shaft D is rapidly returned to its normal
position by the spring L, the nuts N strike the conical split bush M, which bush is
thereby forced into the conical seat in the cradle J, and the said bush.is thus made
to close tightly on or grip the cutter shaft D and prevent it rebounding, so that the
comb or comb nut F falls into the regulator screw G immediately, and begins
another cut without loss of time.
Having now described the nature of my Invention and the manner in which the
same is to be performed, I wish it to be understood that I do not limit myself to the
precise details herein described and illustrated, as the saine may be varied without
departing from the nature of my Invention, but I claim as my Invention of improve-
ments in machinery for threading screws, the construction and combination or
arrangement of the parts of mechanism, herein-before described and illustrated in

page_text: the accompanying Drawing, for rapidly throwing into gear those parts of the said
machinery by which the traversing motion of the thread cutting tool is effected, that
is to say, forming in the rocking cradle of the machine a conical seat for receiving a
divided conical bush through which the cutter holder shaft slides, by the action of
which parts, in conjunction with screw stop nuts on the cutter holder shaft, the said
shaft on making its return.motion is rapidly brought to rest without rebound or
vibratory motion, and the comb or comb nut rapidly brought into gear with the
regulator screw, substantially as described and illustrated.
In witness whereof, I, the said Thomas Garnett, have hereunto set my hand
and seal, this Thirty-first day of May, in the year of our Lord One
thousand cight hundred and seventy-seven.
Witness,
RICHARD SKERRETT,
Clerk to George Shaw,
Birmingham.
THOMAS GARNETT. (L.S.).