Improvements in Toothed Wheels for Chain Gearing.
Year: 1897

page_text: Date of Application, 18th Feb., 1897
PROVISIONAL SPECIFICATION.
Improvements in Toothed Wheels for Chain Gearing.
I, THOMAS ALFRED HEARSON, of Cooper's Hill, Englefield Green, Surrey,
Professor of Engineering, do hereby declare the nature of this invention to be
as follows:
'
I make my toothed wheel for chain gearing with not more than two or three
working teeth whatever be the size of the wheel, instead of constructing it with
such a number that they are at a distance apart equal to the pitch of the chain
as is usually done. These two or three teeth I place apart from one another,
measured along the circumference of the pitch circle, at a distance which is an
integer multiple of the pitch of the chain.
In order to maintain the chain on the portion of the periphery of the wheel
between two teeth I provide flanges as in a flanged pulley, or spiked teeth of
small dimensions to enter the spaces between the links of the chain; and in order.
that after the chain has become stretched or worn the chain may fit accurately over
the working teeth, I construct the periphery of the wheel so that the length
between each two consecutive working teeth may be adjustable.
In one constuction in which only two working teeth are used, which are all that
are necessary when dealing with the larger of the two wheels connected by the
chain, I form the teeth at the two ends of a diametral piece constructed in such a
way that it may be secured to the revolving axle, and the periphery, which is
separately made, is divided at one part of its length so that it may be opened to an
adjustable diameter. This adjustable periphery I suitably secure to the diametral
piece. Further, to facilitate the manufacture of the periphery of the wheel I
take a length of rolled metal of channel section and having wound it round a
mandril in the form of a helix, 1 divide it into portions of suitable length and
bend them to the correct form for wheel peripheries.
Din 10th day of hobruary 1807
I, THOMAS ALFRED HEARSON, of Cooper's Hill, Englefield Green, Surrey,
Professor of Engineering, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
The nature of this invention is such that a toothed-wheel for chain-gearing may
be constructed in such a way that all the teeth are omitted except such a number,

page_text: so disposed, that under any circumstances there will be always one tooth in
position for action.
To maintain the chain on the wheel, at the parts of the periphery where the
teeth are omitted, flanges are provided as in a flanged-pulley; and to ensure the
accurate coincidence of a tooth with the space between the links of the chain
intended to receive it, both when the chain is new and also when it is worn and
stretched, the portion of the periphery between-two consecutive distant teeth is
made to a length which is approximately an integer multiple of the pitch of the
chain, and is constructed so that this length may be adjusted to an exact multiple
when the pitch of the chain has appreciably increased by wear.
This invention consists in the means whereby these objects are attained which
may be described as follows.
The necessary number of teeth, so that always one may be in position for action,
are formed at the two ends of a diametral piece the central portion of which is
constructed so that it may readily be secured to an axle.
The periphery of the wheel, when it is separately made, is a flanged rim which
is cut at one or both ends of a diameter and means are provided for separating the
ends, formed by the parting, to an adjustable amount. The rim so split is
mounted on the diametral piece on which the teeth are formed so as to be capable
of being rigidly secured to it in any adjusted position.
When the rim is cast with the diametral piece it is first machined and then
parted from one end of the diametral portion and means are provided for separating
the ends.
Figs. 1 to 6, Sheet 1, show the details of construction of the wheel in the case in
which the separately made periphery is split at one end of the diameter only.
Figs. 7, 8 and 9, Sheet 2, show the construction when the separately made
periphery is parted at both ends of a diameter.
In both constructions, the example chosen for illustration is that in which the
circumference of the pitch circle of the wheel is an odd multiple of the pitch of
the chain, viz. 19. That there may, in this case, be always one tooth in position
for action, it is necessary to provide 2 teeth at one end of the diametral piece, these
two teeth being at a distance from one another of one pitch measured from centre
to centre. This distance is not adjustable. At the other end there is only one
tooth. If the circumference of the pitch circle of the wheel is an even number
of pitches, one tooth at each end of the diametral piece will generally suffice for
the transmission of effort to or from the chain; but, if the wheel is the smaller
one of two joined by a chain, or, if the chain is used very slack, it may be advisable
to provide two teeth at each end in order to avoid the possibility of slipping a
link.
Referring to Sheet 1, Fig. 1 is a side elevation partly in section:
Fig. 2 is a diametral section:-
Fig. 3 is an end elevation: -and
Fig. 4 is a section of the rim.
To one end of the diametral piece the double-ended screw shown separately in
Figs. 5 and 6 is rivetted. The periphery is parted at one portion of its length and
a piece with a hole to fit the screw is rivetted to each side. The T pieces are
sprung over the ends of the screw and thus each end may be held in a rigidly
adjusted position by means of a nut and lock-nut as shown in Fig. 1.
Holes are provided in the rim through which the teeth at the other end of the
diametral piece are inserted with an accurate fit. A screw or rivet is employed to
make the attachment secure.
When the rim is cast with the diametral piece it is first machined and then one
end of each half is parted, by a saw-cut, from the diametral piece, and the adjust-
ment of each half is effected by an inwardly projecting flange from the cast rim,
and by a screw and a pair of nuts as shown in Figs. 1, and 2. Each half of the
rim may be severed from the same end of the diametral piece and a double-ended
screw used, as shown in Figs. 5 and 6, or one half of the rim may be severed from

page_text: one end of the diametral piece and the other from the other end, two single-ended
screws being used. In this case each half of the wheel will be like the other half.
If a portion of one side of the rim be omitted at the part which immediately
follows a tooth, as shown in Fig. 1, then, whilst the chain will be unable to leave
the rim when running forward, it may be drawn sideways off the wheel when the
motion is reversed. Under these circumstances an endless chain of which every
joint is rivetted may be used.
Referring to Sheet 2, Figs. 7, 8 and 9 show an alternative method of construction
which may be adopted when the rim is separately made. In this case the rim is
provided with two apertures suited to fit the two ends of the diametral piece on
which the teeth are formed, and the rim is divided into two similar halves by
cutting it partly through at one end of the aperture, and completing the severance
at the other end as is shown in Figs. 7 and 8.
Each half is pivoted to the diametral piece, one at one end and the other at
the other end, and the second end of each half is provided with an elongated hole
permitting of an adjustment when the pivoting screws are slackened. At each
end there is also a screw by which the halves of the rim are maintained in precise
adjustment to suit the pitch of the chain.
In the Figures two additional arms are shown at right angles to the diametral
piece. These, if added, would help to keep the two portions of the rim rigidly in
a plane normal to the axis of revolution.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be be performed, I declare that what
I claim is:-
1. A toothed-wheel for chain-gearing having one or two teeth formed at each
end of a diametral piece, by means of which the wheel is mounted on an axle, and
in which each half of the periphery, extending from one end of the diametral
piece to the other, is either pivoted at one end, or, being rigidly secured at that
end, is sufficiently elastic that the other end may be set to an adjusted position
in order that the distance along the rim, from a tooth at one end of the dimetral
piece to a tooth at the other end, may be made an exact multiple of the pitch of
the chain.
2. A toothed-wheel for chain-gearing constructed substantially as described
and shown in Figs. 1 to 6 Sheet 1.
3. A toothed-wheel for chain-gearing in which a flanged rim cast with the
diametral piece on which the teeth are formed is partially severed from the
diametral piece and made adjustable substantially as described.
4. A tocthed-wheel for chain-gearing constructed substantially as described
and shown in Figs. 7, 8 and 9, Sheet 2.