IMPROVEMENTS IN SCREW GEAR
Year: 1884

page_text: We JAMES HENDERSON ABERCROMBIE of 110. Elderslie Street, Glasgow, in the
County of Lanark Engineer; and JOHN SNODGRASS BRYCE of 11 Hunter Street,
Paisley, in the County of Renfrew, Engineer, do hereby declare the nature of our
said Invention, for "IMPROVEMENTS IN SCREW GEAR" and in what manner the
same is to be performed, to be particularly described and ascertained in and by
the following statement ;-
Our Said Invention, which relates to improvements in Screw or worm gearing
is applicable to such gearing for whatsoever purpose it may be used or adapted
and the Invention has for its object to lessen or diminish the friction and loss of
effect consequent on the construction of screw gearing as hitherto or ordinarily
inade.
The Invention consists in substituting for the ordinary teeth of worm wheels,
studs or pins which are cast or fixed in any convenient manner in the rim of the
wheel so as each to form the axis of a roller capable of revolving around its pin
or stud.
The worm screw is of the usual form but on account of the construction of the
wheel it is proportionately coarser in pitch than an ordinary screw for effecting
the same work, and, as it rotates, the thread of the screw bears on the rollers and
causes the worm wheel to revolve.
And in order that our said Invention may be more clearly understood, we have
hereunto appended an explanatory sheet of drawings with reference to which we
now proceed more particularly to describe the system or mode of using or
performing the same.
Figure 1, of the drawings is an elevation, partly in section of a screw or worm
gear constructed in accordance with our said Invention, figure 2 is a plan, and
figure 3 a transverse vertical section of the same.
As shewn by these figures and more especially at, A, figure 1, a series of studs
or pins, formed with conical necks, are fixed around the periphery or rim of the
worm wheel B, by the nuts b, in lieu of the ordinary worm wheel teeth; and these
The rim of
studs or pins A, constitute axes for a series of rollers C, to revolve on.
the wheel in the direction of its circumference has a flat portion D; formed on it,
DC1

page_text: under each roller, to afford a proper bearing and the rollers may be held in position
against the rim by flat or "cheese" heads formed on the studs or pins and
countersunk into the rollers, as shewn at E, figure 1, or as seen in elevation at
figure 4, in plan at figure 5, and in transverse section at figure 6; cheeks F,
be formed on and project outwards from the rim of the wheel and the studs or
pins made with " tee heads G, which rest in recesses or grooves made, in the
cheeks for their reception.
may
By this latter arrangement the studs A, are supported at both ends but they
may be secured or fixed in any convenient and efficient manner, other than those
shewn on the drawings, or they may be cast on the rim of the wheel B.
The inner side of the rim may have flattened portions, as at D, figure 1, for the
nuts b, retaining the studs or pins A in position to bear against; but to save
surfacing at the said points, it is preferred to form the inner side of the rim curved
or partly spherical, as seen at figures 3, and 6, and to correspondingly curve the
bearing faces of the nuts b, The same construction may be applied with reference
to the rollers C, that is to say, instead of flattening the rim under the rollers, as
herein before, described it may be convex or partly spherical in the direction of its
breadth, the radius being struck from the centre of the wheel at right angles to
the circumference.
In the breadth of the rim one roller only may be used, as seen at figures 2, 3,
and 5, or as shewn in section at figure 7, and in plan at figure 8, two or more
rollers may be used in the breadth of the rim. When this arrangement is adopted
the studs or pins A, constituting the axes of these rollers are so arranged that all
the rollers C, in the breadth of the rim shall be acted on with turning effect to the
wheel, by the thread of the screw H.
The use of the rollers C, in lieu of ordinary worm wheel teeth involves much
less loss of effect by friction, than in ordinary screw gearing and to still further
reduce the loss by friction, an annular space may be made between the rollers C,
and the studs or pins A, which space may be filled vertically and circumferentially
with a series of antifriction rollers d; or instead of such rollers, a series of balls or
spheres may be employed to fill the space as seen at e, figure 1.
For the same purpose as seen at figure 9, a series of balls or spheres f, may be
interposed between the ends of the worm or screw E, and the bosses or cheeks
which retain it in position. These balls or spheres are situated partly in grooves
running round the ends of the bosses or cheeks and partly in grooves running
round the ends of the worm or screw E, and a sufficient number of them are
employed to fill the said grooves circumferentially, or instead of such balls or
spheres coned rollers, or equivalent roller devices may be so interposed as seen at g,
figure 9, it being understood that these ball or roller bearings for the worm
screw H, form no part of our said Invention.
With screw gearing constructed as herein before described in any case where it
may be advantageous or desirable to prevent the possibility of a resistance or
pressure exerted through the worm wheel B, on the screw or worm H, causing the
screw to revolve, the wheel and worm or screw H may be placed at an angle
relatively with each other as indicated at figures 9 and 10, that is to say, in such
a position that the pressure of the rollers C, on the thread of the screw or worm H,
will be normal or nearly so and thus have no turning effect.
The studs or pius A, the rollers C, and the antifriction rollers or balls, d, e, f, g,
may be made of iron, steel or equivalent material and the rollers C, may be in
outline similar to the teeth of spur wheels or of any other suitable contour.
Having now particularly described and ascertained the nature of our said
Invention and in what manner the same is to be performed, we declare that what
we claim is :—
First The substitution in screw gearing of studs or pins A, in combination
with rollers C, for the ordinary teeth of worn wheels substantially as and
for the purposes hereinbefore described with reference to the appended drawings.

page_text: Second The combination of the studs or pins A, rollers C, and antifriction
rollers d, or antifriction balls or spheres e, in worm wheels of screw gearing
substantially as and for the purposes hereinbefore described with reference to
figure 1 of the drawings annexed.