A COMPOUND CRANK FOR CHANG- ING A CIRCULAR MOTION INTO A RECTILINEAR ONE, AND VICE VERSA, WHICH IS APPLICABLE TO VARIOUS MECHANICAL PURPOSES
Year: 1801

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, GEORGE
MEDHURST, of St. James, Clerkenwell, in the County of Middlesex, Engineer,
send greeting.
WHEREAS His most Excellent Majesty King George the Third, by
His Letters Patent, bearing date at Westminster, the Twenty-seventh day of
January in the forty-first year of His reigu, did grant unto me, the said
George Medhurst, His especial licence and authority that I, the said
George Medhurst, my executors, administrators, and assigns, might lawfully
make, use, exercise, and vend, within England, Wales, and the Town of
Berwick-upon-Tweed, my Invention of "A COMPOUND CRANK FOR CHANG-
ING A CIRCULAR MOTION INTO A RECTILINEAR ONE, AND VICE VERSA, WHICH IS
APPLICABLE TO VARIOUS MECHANICAL PURPOSES;" in which said Letters Patent
there is contained a proviso obliging me, the said George Medhurst, within
one calendar month from the date of the said Letters Patent, to cause a
particular description of the nature of my said Invention, and in what manner
the same is to be performed, by writing under my hand and seal, to be enrolled
in His Majesty's High Court of Chancery.
NOW KNOW YE, that in compliance with the said proviso, I, the said
George Medhurst, do hereby declare that my said Invention is described in
manner following, that is to say:-
In the first place I proceed to lay down and explain the general truths or
considerations upon which my said Invention is built and established, so as to
exhibit a true explanation of the figure and effect of the said compound crank;

page_text: and, in the next place, I shew the chief or most simple and valuable construc-
tion of the same.
In Figure 1 the line A, B, represents a lever capable of revolving on
its extremity A, in which case its other extremity B would describe
the circle B, D, E, suppose in the direction marked by the small arrow F.
The line B, C, also represents a lever of the same length, fixed to the
end B of the former lever, and capable of revolving on the extremity B,
while that point is carried round by the former motion of A, B. Admit
now that the lever B, C, shall be moved in the direction of the small
dart G, while A, B, moves as first described, and that the true or abso-
lute angular velocity of both shall be equal, it will evidently follow that
the point C will be moved in a right line towards A, and as the rotation
continues it will pass it until both levers become placed in the same strait
direction on the side towards D, after which the same point C will return
along the same right line until it shall have arrived at an equal distance on
the opposite side towards H, and in this manner will the alternate back-and-
forward motion in a right line continue so long as the rotatory motion round A
shall continue; and these motions may respectively cause each other, accord-
ing to the well known properties of mechanic engines. And I do declare that
in the said Figure 1 is delineated the general nature and constructure of my
said compound crank in its simplest state, and that I do hereby assert my
claim and right to the exclusive use of the same (according to the true intent
and meaning of the said Letters Patent herein-before recited and referred to),
whatever may be the form and structure of the apparatus or geer by means of
which the motion of A, B, and the correspondent equal angular motion of
B, C, may be produced, because there are several ways of making and
applying apparatus or geer for those purposes which will without difficulty be
recurred to by any man of skill and information sufficient to be imployed in
works of this nature. But as it may conduce to the fuller and more perfect
instruction of such as may hereafter construct my said Invention, if several
pieces of machinery acting by means of the said compound crank be. here
delineated and described, I shall proceed-to-shew-some-of_the_best_construc-
tions, first premising that I do not affirm that these are the only methods of
operating with my said compound crank, and that I do hereby claim the
exclusive priviledge and use of the methods, or, constructions here shewn, as far
as their originality, use, or application may lawfully intitle me thereunto, by.
virtue of His Majesty's Letters Patent unto me granted as aforesaid..
Figure 2 represents the compound crank with its parts put together, so as
to act upon each other, and produce. the effect proposed. A is a dead. or

page_text: motionless wheel. B is a spindle which passes through and turns in the centre
of the same, and has the arm G fixed to it at right angles.---Upon this arm at
C is a fixed pin, that serves as the centre of a second wheel E, the teeth.of
which lock into those of A. This wheel E, therefore; revolves on its pin
whenever the lever or arm G is moved, and thereby turns the smaller wheel
D, which contains half the number of teeth that A has. The axis of the
wheel D passes through the extremity of the 'arm G, and on the end of that
axis, on the other side of C, is fixed the arm H, of equal length to the arm G;
then, if a circular motion be given to axis B carrying round the arm G, the.point
F in the arm H will describe the right line I, N; or, if a rectilinear. motion be
given to the point F, any point of the arm G will describe a circle. To drive
the axis B, a wheel P may be fixed and moved by the worm Q upon the
spindle Q, R, from which the crank will receive its motion; or, if a more
uniform motion and power be required, I fix upon the axis B (see Figure 3) a
toothed ellipsis, the transverse diameter of which is parallel to the arm G,
which ellipsis is turned by the teeth of a conical pinion Q upon the spindle
QR, the smaller diameter of which pinion is placed towards R. The motion
of F may be thus rendered uniform, or accelerated or retarded at pleasure, in
the various parts of its progress, accordingly as the dimensions and figure of
the wheel P and its pinion are changed, or others substituted in their place,
-in which cases it is not necessary that elliptical or conical forms should be
adhered to, but a great variety of other figures may be adopted, which may
easily be deduced from the nature of the motion intended to be produced.
And the same effects of modified velocity in F may also be produced by giving
an elliptical figure to the wheels of the apparatus, Figure 2, and causing them
to revolve on their centres, so as respectively to give motion in train to
each other.
Figure 4 is a side view of the compound crank. A is the dead wheel
fixed to the part of the frame, XX; B is the axis which passes through the
dead wheel and the part X, X, of the frame, and is attached to the arm G,
which carries the intermediate wheel C and smaller wheel D, whose axis
passes through the arm G, and is fixed to the arm H.
.
Figure 5 represents a compound crank, in which the wheel D receives its
motion from the wheel A by an endless chain X, X, instead of an intermediate
wheel.
Figure 6 represents the manner of giving the proper motion to the joints of
the compound crank by a parallel axis, whereby to obtain the range of the.
point F in the most compact manner: A is the dead wheel, with perpendicular'
or bevel teeth; B, the axis--of-the arm G; which turns in the centre of 'A.

page_text: D is a wheel of half the size of A, and has also perpendicular or bevil teeth.
The axis of this wheel passes through the arm G, and to it is firmly fixed the
arm H, F. 0, 0, is a spindle which turns in a socket fixed at each end of it,
which sockets are fixed to the arm G. Upon one end of the spindle is fixed a
wheel L, the teeth of which work in the perpendicular teeth of the dead wheel
A, and give motion to the spindle 0, 0, as the arm G is turned round. Upon
the other end of the spindle O, O, is fixed another wheel M, equal in diameter
to L. This wheel gives motion to the wheel D, and consequently to the
arm H, F.
Figure 7 represents the manner of connecting or combining the levers or
arms of my compound crank by any number of repetitions or to any extent.
The dead wheel A, the axis B, arm G, wheel D, spindle O, O, and wheels L
and M, are in the same position as in Figure 5. The arm H, F, is of twice
the length of G, and arm K is of equal length to G. Upon the end of the
arm G, and concentric with the wheel D, is a larger wheel, fixed to the arm
H, F. This larger wheel, having upright bevel or contrate teeth like A,
drives the wheel P and the spindle Q, Q, which, by its wheel R at the farther
extremity, drives S, and consequently the arm K, I. The wheel S is half the
diameter of N. In this manner it may easily be understood that any number
of jointed levers may be made to move after the manner of my compound
crank by means of the gear here described, or any other proper connecting
apparatus by wheel chain or otherwise. And for the further clucidation of
this truth it may be proper to advert to Figure 8, where the lines A B, BC,
CD, DE, EF, represent the levers of a combination of my cranks, moved
according to the conditions herein-before explained. It is clear that the point
G will move along the right line A, L, while A, B, revolves in a circle, and
for the same reason, namely, because G, C, is relatively moved in a circle, the
point H will move in the right line before mentioned; and so likewise will the
points I and F, wherein it is farther to be noted, that, whatever may be the
respective lengths of the arms, the wheelwork or connecting gear must be so
proportioned that the true or absolute angular motion of every one of the arms-
shall be equal, and the point F or end of the last lever must be placed in a
line drawn through the first centre A and the point G, which terminates the
first compound crank.
Figure 9 shews one of the methods of applying a compound crank to a
mangle. N, N, N, N, is the top of the mangle frame. X, X, is the frame of
the crank, fixed upon the middle of the frame.
A is the dead wheel, fixed to
two studs on the inside of the crank frame. These studs admit a wheel E
between them, with inclining teeth fixed upon the spindle B of the crank

page_text: arm C. This wheel E is turned by the worm E and spindle F, which receives
its motion by the handle M, and the motion is regulated by a fly-wheel on the
other end of the spindle.
Figure 10 illustrates the use of a compound crank in a wind, steam, or
water engine, in which the parallel motion of the piston rods is preserved by
being attached to the end G of the compound crank, the dead wheel of which
is fixed to the timber X, X, and the arms C and wheels C and D revolve round
it, as in Figure 2 and 3.
The compound crank may be applied with advantage to, 1st, Steam, wind
or water engines, or air cylinders. 2d, Mangles and callenders. In order to
obtain a sufficient degree of strength in the frame of the mangle for the
compound crank to have the best effect, I make the frame of cast-iron, each
side in one piece. 3d, Glazing calico, linen, &c. 4th, ruling parallel lines.
5th, Sawing of timber and stone; and generally to every other object in which
the conversion of a rotatory motion into a right-lined motion, or the contrary,
is required to be effected.
In witness whereof, I, the said George Medhurst, have hereunto set my
hand and seal, the Twenty-sixth day of February, in the year of our