Improvements in Apparatus for Cutting the Teeth of Wheels for Screw Gears, specially applicable to Worm-wheels and Worms.
Year: 1895

page_text: Date of Application, 10th Dec., 1895
Complete Specification Left, 10th Sept., 1896-Accepted, 24th Oct., 1896
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Cutting the Teeth of Wheels
for Screw Gears, specially applicable to Worm-wheels and
Worms.
I, JOSEPH HAMILTON GIBSON, of 12 Brattan Road, Birkenhead in the
County of Chester, Engineer, do hereby declare the nature of this invention to be
as follows:-
This invention relates to apparatus for cutting the teeth of wheels for screw
gears, and is specially applicable to worm wheels and worms.
The teeth of worm-wheels are at present cut by means of a worm similar to the
one with which the wheel is designed to engage but having cutting edges produced
by grooving it after the manner of a tap; the necessity of making a cutting worm
of this kind for each different size of worm employed renders this process a some-
what expensive one, and the object of my invention is to dispense with the cutting
worm and to substitute for it an ordinary rotating cutting tool.
It will be seen that when a cutting worm is employed as described it serves both
to cut the teeth and to rotate the worm-wheel which is being cut; according to my
invention, however, I employ a rotating tool which merely effects the cutting, and
I independently rotate the worm-wheel by suitable change gear. The shape of
the teeth produced by both processes is the same, as it is evident that the rotating
tool may be regarded as one of the many cutting edges of the cutting worm, the
necessary relative movement between the tool and the worm-wheel being produced
by the independent means.
A machine for cutting screw gear according to my invention, broadly described,
comprises the following;-A standard worm-wheel operated by a driving worm on
the driving shaft, and adapted to form a face-plate on which the wheel to be cut
is secured; a cutter shaft carried in bearings capable of adjustment relatively to
the standard worm-wheel, and adapted to carry the cutter; change wheels for
rotating the cutter shaft at the required speed relatively to the standard worm-
wheel; means for moving the cutter relatively to the cutter shaft, or to the driving
wheel on the cutter shaft, so that, during the process of cutting, the cutting edge
may occupy successive positions on an imaginary helical curve of pitch equal to
that of the worm with which the wheel to be cut is adapted to engage; and an
automatic device whereby the rotation of the standard worm causes the cutting
edge of the cutter to occupy these successive positions.
The standard worm-wheel is pivoted on a vertical axis, and the face plate, to
which the wheel to be cut is secured, is attached directly to the standard worm-
wheel, so that the wheel to be cut is driven by the latter without the driving force
having to be transmitted through a mandrel; the standard worm-wheel is supported
by conical rollers which take the pressure of the cut.
The driving shaft and the cutter shaft are preferably arranged on opposite sides
of the worm-wheel, and the usual arrangement of quadrants, to carry the change
wheels, is provided so that the latter shaft can be driven from the former at any
required velocity ratio.
The necessity for moving the cutting edge to occupy successive positions on an
imaginary helix corresponding to the engaging worm, will be understood when it is
borne in mind that in the ordinary method of cutting the teeth of worm-wheels by

page_text: means of a grooved worm, the teeth are formed by several cutting edges, each
rotating in a different plane; and I have found it necessary in cutting the teeth
according to my invention, to move the cutting edge so that it occupies successive
positions corresponding to the various cutting edges of the grooved worm.
The
cutting edge may be made to occupy these successive positions by making the tool
box in the form of a nut adapted to engage with a worm, on the cutter shaft,
corresponding with the engaging worm of the wheel to be cut, and gradually
rotating the said tool box, relatively to the cutter shaft, on this worm as the shaft
rotates. This method, however, introduces certain structural difficulties and
I prefer to adopt the following method.
The driving end of the cutter shaft is screwed to a pitch corresponding to the
worm adapted to engage with the worm-wheel to be cut, and a screwed bush or
nut screws on to this end of the shaft; the wheel which drives the cutter shaft is
keyed on this bush, but the bush is normally prevented from turning relatively to
the cutter shaft by being attached to a disc, which disc is feathered in a key-way
in the cutter-shaft, and so rendered capable of axial movement but not of rotational
movement, relatively to the shaft. It will be seen that relative movement between
the bush and the disc will result in the shaft being screwed into or out of the bush,
and as the latter is prevented from moving axially relatively to the worm-wheel
this screw motion causes the cutting edge to travel in the desired helical path.
The movement of the cutter is effected gradually, as the cutting proceeds, by
fixing toothed wheels on the bush and on the disc; the wheels are equal in
diameter but the one has one or two teeth more than the other, and a third wheel
gears into each and rotates bodily, so constituting an epicyclic train, and the
necessary relative movement between the disc and the bush is effected by causing
the standard worm-wheel, as it rotates, to operate the third wheel of the epicyclic
train.
The machine can be adapted to cut worms, more especially hollow worms, by
mounting one or more tools in the standard worm wheel, and carrying the worm to
be cut on the cutter shaft.
Dated this 9th day of December 1895.
SLOAN & LLOYD BARNES,
26 Castle Street, Liverpool, Agents for the Applicant.
Improvements in Apparatus for Cutting the Teeth of Wheels
for Screw Gears, specially applicable to Worm-wheels and
Worms.
I, JOSEPH HAMILTON GIBSON, formerly of 12 Brattan Road, Birkenhead, but
now of 11 Glenalmond Road, Egremont, both in the County of Chester, Engineer,
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 :-
This invention relates to apparatus for cutting the teeth of wheels for screw
gears, and is specially applicable to worm-wheels and worms.
The teeth of worm-wheels are at present cut by means of a worm similar to the
one with which the wheel is designed to engage but having cutting edges produced
by grooving it after the manner of a tap; the necessity of making a cutting worm
of this kind for each different size of worm employed renders this process a some-
what expensive one, and the object of my invention is to dispense with the cutting
worm and to substitute for it an ordinary rotating cutting tool.
It will be seen that when a cutting worm is employed as described, it serves both

page_text: cern and to rotate the worm-wueel which is being cut; according to my
invention, bowever, I employ a rotating tool which merely effects the cutting, and
I independently rotate the worm-wheel by suitable change gear. The shape of
the teeth produced by both processes is the same, as the rotating tool may be
regarded, as hereinafter described, as the equivalent of the many cutting edges of
the cutting worm, the necessary relative movement between the tool and the
worm-wheel being produced by the independent means for rotating the wheel.
A machine for cutting screw gear according to my invention, broadly described,
comprises the following;-A standard worm-wheel operated by a driving worm on
the driving shaft, and adapted to rotate a face-plate on which the wheel to be cut
is secured; a cutter shaft carried in bearings capable of adjustment relatively to
the standard worm-wheel, and adapted to carry the cutter; change wheels for
rotating the cutter shaft at the required speed relatively to the standard worm-
wheel; means for moving the cutter relatively to the cutter shaft, or to the driving
wheel on the cutter shaft, so that, during the process of cutting, the cutting edge
may occupy successive positions on an imaginary helical curve of pitch equal to
that of the worm with which the wheel to be cut is adapted to engage; and an
automatic device whereby the rotation of the standard worm wheel causes the
cutting edge of the cutter to occupy these successive positions.
In the accompanying drawings which illustrate my invention, Fig. I is a plan,
partially in horizontal section through the axis of the cutter shaft; Fig. I is a
side elevation; Fig. III is an end elevation; and Fig. IV is a sectional elevation
on the line A. A. of Fig. 1.
Throughout the drawings the sar. e parts are indicated by the same reference
figures.
1 is the standard worm-wheel, rigidly mounted on the vertical shaft 2 to which
the face-plate 3 is rigidly attached; the shaft 2 is carried in the bushed bearing 4,
secured to the main frame 5.
The worm-wheel blank to be operated upon, is indicated at 6 in dotted lines,
(see Fig. IV), and it is rigidly bolted to the face plate 3; the mandrel 7, with
changeable collar 8, being provided to accurately centre the blank, and the
packing pieces 9 being used to adjust the height; the slots 10 are provided in
the face plate for additional bolts if required, and in the case of a blank of unusual
diameter, it may be further supported in the vicinity of the cutting action by a
bearing roller carried in a detachable frame.
11 is the driving worm for the standard worm-wheel, cotiered on the driving
shaft 12 and operated by the stepped pulley 13; back-gearing to reduce the
speed is not shown, but would be fitted in the case of a machine intended to cut
coarse pitches. The thrust collars 14 to the worm 11 have a screw adjustment so
as to prevent backlash.
The cutter shaft 15 carrying the cutter 16 is mounted in bearings carried on the
transverse slides 17 and 18, so that it can be adjusted to suit blanks of different
diameters. These slides may be provided with the usual traversing screws and
handles, or they may be simply slid to the proper positions and there secured by
tightening the slide strips 19. The bearing 20 for the left end of the shaft 15 is
also adapted to slide longitudinally, by being mounted on the slide 21, so as to
permit of the axial motion of the shaft 15 as hereinafter described.
The driving shaft 12 and the cutter shaft 15 are geared together by change wheels
so as to give the appropriate velocity ratio between the worm-wheel blank and the
shaft 15, this being the same as that between the finished worm-wheel and the worm
shaft gearing with it.
These change wheels are carried on adjustable studs in the well known manner, the
swing frame 22 and the slots 23 (see Fig. III) being provided for carrying the
studs; owing to the length of the swing frame, it is preferably clamped by a strut
such as 24 and a bolt 38 in one of the slots. By way of example, a set of seven
chauge wheels 25 is shown in the drawings.
The last change wheel is not attached directly to the cutter shaft 15, but to the

page_text: nut 26 which forms the journal for this end of the shaft; the object of this is to
provide for the adjustment of the cutter relatively to the driving wheel of the
cutter shaft, already referred to.
The
The necessity for moving the cutting edge to occupy successive positions on an
imaginary helix corresponding to the engaging worm, will be understood when it
is borne in mind that in the ordinary method of cutting the teeth of worn-wheels by
means of a grooved worm, the teeth are formed by several cutting edges, each
rotating in a different plane; and I have found it necessary in cutting the teeth
according to my invention, to move the cutting edge so that it occupies successive
positions corresponding to the various cutting edges of the grooved worm.
cutting edge may he made to occupy these successive positions by making the tool
box in the form of a nut adapted to engage with a worm, on the cutter shaft, corre-
sponding with the engaging worm of the wheel to be cut, and gradually rotating
the said tool box, relatively to the cutter shaft on this worm as the shaft rotates.
This method. however, introduces certain structural difficulties and I prefer to adopt
the method illustrated.
The shaft 15 is screwed to a pitch corresponding to the pitch of the worm
adapted to engage with the worm-wheel blank to be cut, and is accurately fitted
within the nut 26, carried in the bearing 18; this nut 26 is provided with the thrust
collars shown, to prevent axial motion.
The rotation of the nut 26 is conveyed to the shaft 15 through the dise 27
which rides over the threads and is feathered in a key-way 28 on the shaft,
but the nut and the disc are not rigidly connected, and it will be seen that
relative angular movement between them will result in the shaft being screwed
into or out of the nut, and as the latter is prevented by its thrust collars
from moving axially relatively to the worm-wheel blank, this screw motion
causes the cutter 16 to be adjusted to successive positions in the desired helical
path.
This movement of the cutter is effected, as the cutting proceeds, by means of
the gear wheels 29 and 30, formed integral with or attached to the nut 26 and the
dise 27 respectively. These wheels are equal in diameter but the one has one or
two teeth more than the other. They each gear with the epicyclic wheel 31
carried on the frame 36, fixed to the disc 27, and provided with the balance
weight 37; rotation of this wheel relatively to the other two will evidently cause
the desired relative angular movement between the disc 27 and the nut 26, and so
effect the desired adjustment of the cutter 16.
The wheel 31 is operated automatically through part of a revolution, each time
the worm-wheel blank makes a complete revolution, by means of the star wheel 32
(similar to those commonly used for such a purpose) adapted to engage with the
rod 33. This rod is moved axially, so as to engage at the appropriate time with
the star wheel, by the rocking lever 34, which is deflected, at each revolution of
the worm-wheel blank, by the cam surface 35 attached to the face plate; a
spring, not shown, is provided to urge the rod 33 out of engagement with the
star wheel, and a series of holes for the articulation of the rod to the lever is
provided in the latter, to suit different positions of the slide 17 which carries the
bar 33.
The operation is as follows;-
The star wheel 32 is turned by hand so as to bring the cutter 16 well over
to the right or left, (as the case may be according to the direction of the cutting),
of the centre line A. A. (Fig. 1); the slides 17 and 18 are then adjusted so that
when the cutter reaches the centre line A. A. it will sweep out of the blank the
full depth of the tooth, and the star wheel is then turned by hand until the cutter,
as it revolves, just begins to cut the blank. The rest of the action is quite
automatic, the effect of the automatic turning or "feeding" of the star wheel
being to traverse the cutter across the centre line A. A. until it ceases to act upon
the worm-wheel blank, when the cutting will be completed.
As the automatic adjustment of the cutter is made once at each revolution of

page_text: the worm-wheel blank it will be observed that the action on every tooth is exactly
alike and that the ultimate result is similar to that which would have been obtained
from a cutting worm having cutting edges corresponding to the successive positions
of the cutter 16.
The machine can be adapted to cut worms, more especially worms of hollow or
concave contour, by mounting one or more cutting tools on the face plate 3 and
carrying the worm to be cut on the shaft 15.
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. The herein described improvements in apparatus for cutting the teeth of
wheels for screw gears, which consists in mounting the wheel to be cut on a
rotatable face plate, and carrying a cutter on a rotatable shaft geared to the said
face plate and provided with means for adjusting the cutter to successive positions
on a helical path; substantially as set forth.
2. The means for effecting the helical adjustment of the cutter 16, comprising
the bearing nut 26 fitting on the screwed cutter shaft 15, the disc 27 feathered on
the cutter shaft, and the epicyclic feed gear; substantially as described and
illustrated.
3. The combination and arrangement of parts forming the improved apparatus
for cutting the teeth of wheels for screw gears; substantially as described and
illustrated.
Dated this 9th day of September 1896.
SLOAN & LLOYD BARNES,
Castle Chambers, 26 Castle Street, Liverpool,
Agents for the Applicant.