Improvements in Screw Cutting Lathes.
Year: 1893

page_text: Date of Application, 27th Nov., 1893
Complete Specification Left, 14th July, 1894-Accepted, 18th Aug. 1894
PROVISIONAL SPECIFICATION.
Improvements in Screw Cutting Lathes.
I, CHARLES JOHNSON, of 11 Holly Bush Street Parkgate Rotherham, in the
County of York, Turner and Fitter, do hereby declare the nature of this invention
for the production of coarse threaded screws to be as follows:-
My invention has for its main object, an improved method of cutting coarse
pitched screws in the ordinary screw cutting lathe.
Instead of the present method of connecting the driving belt from the counter-
shaft to the cones in the headstock, I propose to connect the driving belt of the
lathe, to a pulley keyed to a shaft, which runs in a bracket, bolted, or fastened
with studs & screws to the lathe bed.
On this shaft a pinion is keyed, giving motion to a larger wheel keyed to the
guide screw, thus driving the guide screw in the 1st place, instead of the present
practice of driving the lathe mandrel.
Under the present system, motion is given to the screw-cutting wheels, from a
wheel keyed on the mandrel at the end of the lathe, the motion is then transmitted
through the wheels on the quadrant plate to the guide screw. In cutting coarse
pitches in fact any thread coarser than the guide screw-the guide screw must
revolve quicker than the mandrel of the lathe. Thus, in cutting a screw 1 thread
in 6 inches or 6 inch pitch, with a guide screw 2 threads per inch, we should require
the guide screw to make 12 revolutions while the mandrel makes 1 revolution, thus
requiring large wheels to drive small ones, which means loss of power & great
strain on the teeth of the small wheels. The quadrant plate at the end of the
lathe on which the screw cutting wheels are fixed will remain the same, but the
mode of connecting the wheels I propose to alter in the following manner.
Instead of the wheel on the mandrel driving the other screw-cutting wheels, I
propose that the wheel on the guide screw be the driver, thus reversing the present
method & making small wheels drive large ones.
Thus the wheels would be geared as at present with this improvement.
Instead of gearing up to the lathe mandrel, I propose to carry a shaft through a
bracket, bolted or fastened with set screws to the lathe headstock, communicating
motion from the screw-cutting wheels to the pinion on the cone of the lathe, either
direct or connected up by an intermediate wheel, as the make or present back-
gearing of the lathe might require, as the system can be applied to all ordinary
lathes.
0
This arrangement would be applicable for cutting all coarse pitches, as used on
rolls, rifling guns & other arrangements where coarse pitches are necessary up to
1 thread in 10 feet, or coarser still if required.
As a modification of the above,-
I would omit the bracket & shaft for driving the guide screw, & drive the cone
in the headstock from the countershaft as at present, but would use the bracket &
shaft fastened to the lathe headstock, communicating motion from the pinion on the
cone to the screw-cutting wheels.
This method of itself would be sufficient for pitches ranging between 1 thread
per inch & 1 thread in 15 inches or more, according to the make of the lathe to
which it would be applied.
This method will be useful for other work in addition to screw-cutting, as by
simply disconnecting the back gear in the ordinary manner, motion can be given to
the guide screw while the lathe mandrel is at rest, thus with a tool in the ordinary

page_text: slide-rest set at the proper angle, grooves, keyways &c. can be cut on a shaft before
it leaves the lathe.
A verticle slide-rest can be made to temporily fit in the place of the ordinary
slide-rest, thus making the method of wider application.
Dated this 25th day of November 1893.
CHARLES JOHNSON.
COMPLETE SPECIFICATION.
Improvements in Screw Cutting Lathes.
I, CHARLES JOHNSON of 11 Holly Bush Street, Parkgate, Rotherham, in the
County of York, Turner and Fitter 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 invention has for its main object, an improved method of cutting coarse
pitched screws, in the ordinary screw cutting lathe. By reference to Figures 1 & 2
Sheet 1, & Figures 3 & 4, Sheet 2, it will be seen that instead of the present
method of connecting the driving-belt from the counter-shaft to the cones A in the
headstock B, I propose to connect the driving-belt of the lathe to the pulley C,
keyed to a shaft which runs in the bracket D bolted to the lathe bed E. On this
shaft a pinion F is keyed giving motion to the wheel G on the guide screw H, thus
driving the guide screw as a first motion instead of the lathe mandrel I. Under
the present system, motion is given to the screw-cutting wheels from a wheel keyed
on the mandrel I at the end of the lathe, the motion is then transmitted through
the wheels on the quadrant plate J to the guide screw H.
In cutting coarse pitched screws, in fact any thread coarser than the guide screw,
the guide screw must revolve quicker than the mandrel. Thus in cutting a
screw 8 pitch with a guide screw 2 threads pr. in. we should require the guide
screw to make 16 revolutions while the mandrel made 1 revolution, thus requiring
large wheels to drive small ones, which means loss of power & great strain on the
teeth of the small wheels. The quadrant plate will remain the same, but the mode
of connecting the wheels, I propose to alter in the following manner. Instead of
the wheel K on the mandrel I driving the other screw-cutting wheels, I propose
that the wheel on the guide screw be the driver thus reversing the present method
& making small wheels drive large ones, the guide screw wheel being a driver
instead of a driven wheel, oweing to the guide screw being a first motion instead of
the mandrel.
Thus with the exception of reversing the position of driver & driven, the wheels
will be geared as at present with this further improvement.
Instead of gearing up to the lathe mandrel, propose to carry a shaft
through the bracket L which is fastened with set-screws or studs to the head-
stock B.
On this shaft is a wheel M transmitting motion from the screw-cutting wheels to
the pinion of the cone A as shown in Fig. 4 Sheet 2 through the intermediate
wheel N or direct as shown at M Fig. 11 Sheet 5, the method adopted being
determined by the ratios of the back gearing of the lathe to which it would be
applied, as the new system can be adapted to all ordinary lathes.
Figs. 1 & 2 Sheet 1, & Fig. 3 Sheet 2, shows the wheels in position that would
be required under the new system for cutting a right-handed thread 2 ft. pitch the
drivers 50 × 32
wheels necessary being
the
driven 100 × 48
drivers 120 x 128
present method would require
thus showing at a glance, the advantage of the new system, the
driven 20 × 16
smaller wheels as drivers giving a better distribution of power & less strain on each

page_text: tooth; under the present system, the driven wheels 20 & 16 would sustain very
great pressure, involving the use of stronger screw-cutting wheels & larger lathes
for cutting coarse-pitched screws, the new system will not require another set
of change-wheels, as all the wheels at present in use can be utilized, thus making
them more useful than heretofore.
Another advantage will be, that the coarser the screw to be cut, the greater the
power for cutting it, which is exactly the reverse of the present method. The
cone C Fig. 2 Sheet 1, is fixed on the lathe bed in a line with the cone A the belt
being crossed for right hand threads & run open for left hand threads, the motion
of the lathe mandrel will thus be always in the usual direction, an extra wheel to
be added when left hand threads are required. The sizes of the wheels F & G will
be determined by the speed of the countershaft, & the cutting speed required on the
screw to be cut, the cone C can also have 23 or more steps if required, to vary the
speed for cutting. When finer pitches than the guide screw are required,
the intermediate wheel N (Fig. 4 Sheet 2) can be thrown out of gear by the
bandle b, the collar c Fig. 3. being replaced by a wheel of the same number of teeth
as K, thus causing the spindle in the bracket L to run the same speed as the lathe
mandrel. Fig. 4 is an end view of the sections cut through O, P, & Q, R,
in Fig. 2.
This arrangement will be applicable for cutting all coarse pitches for rolls,
rifling guns &c. & other arrangements where coarse pitches, are necessary up
to 1 thread in 10 ft. or coarser still if required.
As a modification of the above I would omit the bracket D, the shaft & wheels F
& G for driving the guide screw, & drive the cone A. in the headstock B as
at present, but would use the bracket L fastened to the lathe headstock & the shaft
& wheel M communicating motion from the pinion on the cone A to the screw-
cutting wheels.
This method of itself will be sufficient for pitches ranging between 1 thread
pr. inch & 1 thread in 15 inches or more, according to the make of the lathe to
which it would be applied; for treble-geared lathes, this modification will be
almost equal to the method shown in Sheet 1 & 2, owing to the greater difference
in ratios of speed, gained from an internal geared face plate.
Figs. 5 & 6 Sheet 3, shows this modification applied to another type of lathe in
common use, the letters describing its general features, corresponding with the
letters previously used, the end view of the section O, P Fig. 6 being arranged in
the same way as Fig. 4 Sheet 2. The spindle J Fig. 6 is run at the same speed as
the mandrel I, the motion being reversed by the lever X for left-hand threads.
In adapting the new system to this class of lathe, I would extend the spindle J
beyond the reversing wheels Y, so as to key on the wheel Z, connecting motion
through the spindle in the bracket L to the pinion of the cone A. When requiring
the new motion the reversing lever X would be placed in mid-position, thus
allowing the speed of the spindle J to be governed by the new additional wheels.
The number of teeth in the wheels M, A & Z being determined by the ratio of the
back-gear wheels, the principle point to be attained is, that the speed of the
spindle J should be an even ratio of the lathe mandrel I. In Fig. 5 Sheet 3,
driver 50
the wheels necessary to cut a thread 5" pitch are shown
driven 60
the wheels required under the present system consisting of
Fig. 7 shows
drivers 36 x 100
driven 18 × 20
thus
showing the great advantage of even a modification of the new system.
When fine threads below 1" pitch are required, all that is necessary to revert to
the present method, is to lower the intermediate wheel out of gear with the pinion
on the cone C. In Figures 8 & 9 Sheet 4, & Figs. 10 & 11 Sheet 5, are shown the
simplest application of the new system adapted to those whose requirements would
not extend beyond 5 or 6′ pitch. It consists of the bracket L & the wheel M,
geared direct to the pinion of the cone C & in this case containing 32 teeth, the

page_text: number required to bring an even ratio, each of the back-gear pinions having
16 teeth & the wheels 64 teeth thus giving the speed of the wheel & shaft d,
8 revolutions to 1 of the lathe mandrel I. Figures 8, 9, 11, shows the lathe geared
driver 40
Under the present
for cutting a 4" pitch consisting of two equal wheels
drivers 80 x 40
system we should require driven 20 × 20
the simplest application of the new system.
driven 40°
thus showing the great advantage of even
Figures 10 & 11 show how easily this particular form of the new system can be
disconnected when finer pitches than the guide screw are required, by simply taking
off the wheel M & changing the places of the collar c & the wheel d, the spindle in
the bracket is obliged to revolve the same speed, as K & d have each equal
number of teeth.
Some back gears are not an even ratio, for these lathes I would provide brackets
as in Figures 12, 13, & 14, Sheet 6, having two bearings, the bottom one h
carrying the lever X for throwing the wheels in & out of gear; Fig. 12 shows a
section through ƒ & g Fig. 13, the two bearings enable the wheels I & J to
be added, which must contain the odd number of teeth required to bring the speed
of c an even ratio of the mandrel I. The centres of h & k of course being made to
suit the odd wheels I & J, care being taken to fix the bearing k at such a distance
from the mandrel I as to enable two equal wheels to be connected from the lathe
mandrel to the shaft c as shown in Fig. 12, to be used when finer pitches are
required, the intermediate wheel N being thrown out of gear by the handle X.
The equal wheel keyed on c, is replaced by a collar when the new system is
required. Motion can be given to the guide screw independant of the lathe
mandrel by simply disconnecting the back gear in the ordinary way, thus driving
the saddle while the face plate of the lathe is at rest, enabling grooves, keyways &c.
to be cut if desired.
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
1. Driving the guide screw as a first motion, instead of the lathe spindle.
2. Gearing the screw cutting wheels to the cone, pinion instead of the lathe
spindle.
.
Dated thin 19th 1
STI
1004
CHARLES JOHNSON.