Improvements in the Adjustment of Chains for Cycles.
Year: 1899

page_text: Date of Application, 13th Jan., 1899
Complete Specification Loft 44th O
4.000
PROVISIONAL SPECIFICATION.
Improvements in the Adjustment of Chains for Cycles.
We, THOMAS SLACK, Cycle Manufacturer, Wellington Machine Works, Stock-
port, Cheshire, and THOMAS WHITAKER, Cycle Works Manager, 5, Church Street,
Heaton Norris, Stockport, aforesaid, do hereby declare the nature of this inven-
tion to be as follows:-
a
This invention relates to improvements in the adjustment of chains in cycles
whereby the slackness of the chain, consequent upon its wear, is taken up by
special form of eccentric bottom bracket. This eccentric bottom bracket is so
constructed that in moving the eccentric discs to adjust the chain of the cycle,
the distance between the crank axle and the saddle does not alter, and the back
forks can be lengthened or shortened independantly, to make them both exactly
equal and make up any slight error in measurement which the workman may
have made in the length of the back forks.
In machines constructed on the ordinary plans generally used for cycles, the
means for the adjustment of the chain are usually at the ends of the back forks
& stays, on the back wheel axle, the back wheel being usually so constructed as
to slide back from the bottom bracket by means of set screw adjusters. In
another method sometimes employed, the cups carrying the bottom bracket axle
are screwed and locked into an eccentric disc, this eccentric disc being enclosed
in the bottom bracket shell of the cycle frame, the back wheel axle is fixed, and
the chain is adjusted by turning the eccentric disc, thus moving the axle carrying
the front chain wheel and cranks farther from the fixed centre of the back wheel.
In machines constructed in accordance with this invention, the eccentric disc
instead of being all in one piece and enclosed in a large bottom bracket shell,
consists of two eccentric discs, about five eights of an inch wide, which turn upon
the outside edge of the bottom bracket shell, each of these eccentric discs being
enclosed in a separate strap of metal, with a set screw and open end in this strap
to lock it, this strap forms one end of the back fork, so that when the chain is
adjusted instead of the eccentric disc moving the crank axle separate to the
bottom bracket shell, (as is the case with the ordinary eccentric bottom bracket
adjustment), the two eccentric discs move the back forks, separate to the bottom
bracket shell containing the crank axle, and with there being two eccentric discs
moving on the bottom bracket instead of one, the back forks can be moved inde-
pendantly of each other, and any slight error in the lengths of the two back forks
can be made equal, and the back wheel placed exactly in the centre of the back
forks. The adjustment of the chain is then made by the use of a square piece of
metal which is passed through two corresponding holes, one in each eccentric
disc, and the two eccentric discs moved equally together by means of a key on
this square piece of metal, thus shortening or lengthening the back forks, which
tightens or slackens the chain to get the necessary tension. The two eccentric

page_text: discs and the straps carrying the back forks being secured after adjustment by
means of a split in each of the eccentric dises, which locks when the set screws
in the open ends of the straps are screwed up, thus closing the straps on the
eccentric discs.
Improvements in the Adjustment of Chains for Cycles.
We, THOMAS SLACK, Cycle Manufacturer, Wellington Works, Stockport, 1
Cheshire, and THOMAS WHITAKER Cycle Works Manager, 5, Church Street,
Heaton Norris, Stockport, aforesaid, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement:—
This invention for improvements in the adjustment of chains for cycles is an
improvement whereby the slackness of the chain, in consequence of its wear, is
taken up by a special form of eccentric bottom bracket. This eccentric bottom
bracket is so constructed that in moving the eccentric discs to adjust the chain
of the cycle, the distance between the crank axle and the saddle does not alter,
and the back forks can be lengthened or shortened independantly to make them both :
exactly equal, and to make up any slight error in measurement which the work-
man may have made in building up the frame of the cycle.
In machines constructed on the ordinary plans generally used for cycles, the
means for the adjustment of the chain are usually at the ends of the back forks
on the back wheel axle, the back wheel being usually so constructed as to slide
back from the bottom bracket by means of set screw adjusters. In another method
sometimes employed the cups carrying the bottom bracket axle are screwed and
locked into an eccentric disc, this eccentric disc being enclosed in the bottom
bracket shell of the cycle frame, there are no means of adjustment on the back
wheel spindle, and the chain is adjusted by turning the eccentric disc, this moves
the axle carrying the front chain wheel in an eccentric movement to the frame
bottom bracket shell and the chain is thus adjusted to the necessary tension.
In cycles constructed in accordance with this invention, as shown in the accom-
panying drawings, there is no adjustment for the chain on the back wheel spindle,
the back wheel being free to revolve in the centre of the back chain stays B on
the spindle and cones which are locked by nuts E between the back chain fork
ends. C is the bottom bracket shell of the cycle, which is made after any ordinary
pattern in size and shape with the exception that the back chain forks are not
fixtures to it, the back chain forks B are each made in one piece with a strap of
metal open at the front side to receive a set screw K as shown. The eccentric
discs A are fitted on either side of the bottom bracket shell C and made so that
they can be moved round the bottom bracket shell C, (when the set screws K in
the back fork straps B are unfastened) by means of a hole D (or any other suit-
able means,) in one eccentric, exactly opposite a similiar hole in the other eccen-
tric, and through these two holes a piece of metal is inserted to turn the eccentrics
simultaneously. The eccentric discs A have each a slot through them at their
narrowest side so that when the set screw in the back fork straps A are
screwed up, this closes the eccentric discs, and locks them on to the bottom
bracket shell ('. The bottom bracket shell (carries the cups and crank axle in
the ordinary manner and the cups are locked in the bottom bracket shell C at

page_text: the same time the set screws K are screwed up, there being a slot in the bottom
bracket shell on either side at point H as far in as the depth of the eccentric
disc A and this allows the outside edge of the bottom bracket shell C to close and
lock the cups.
The adjustment of the chain is made by loosening the seat
bolt and also loosening the two set screws K, a piece of metal is inserted
through both the holes D and on this piece of metal a wrench or any other
suitable means are used to turn the two eccentric discs A simultaneously so that
the chain is at the right tension, the set screws K in the back chain fork
straps B are then screwed up tight, this locks the eccentric discs A on the
bottom bracket shell C and also locks the cups carrying the crank axle, the seat
bolt is then screwed up, and the piece of metal inserted in the holes D is
removed.
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 :-
(1) An adjustment for the chain of a cycle by means of an eccentric working
on the outside of a bottom bracket bearing.
(2) An eccentric adjusting bottom bracket which allows of the adjustment of
the chain without moving the axle in the bottom bracket bearing.
(3) A method of lengthening or shortening the back chain stays independant
of each other or simultaneously.