IMPROVING THE CONSTRUCTION OF DOUBLE CRANKS, WHEREBY THE MOTION OF THE SHAFT OR JOURNAL THERETO CONNECTED 18 MADE MORE EVEN, AND THE DISTURBING EFFECT OF DEAD CENTRES ALMOST ENTIRELY OBVIATED
Year: 1871

page_text: PROVISIONAL SPECIFICATION left by Edmund Quinn at the Office of
the Commissioners of Patents, with his Petition, on the 30th June
1871.
I, EDMUND QUINN, of Brooklyn, in the County of Kings, and State
of New York, of the United States of America, do hereby declare the
nature of the said Invention for "IMPROVING THE CONSTRUCTION OF DOUBLE
CRANKS, WHEREBY THE MOTION OF THE SHAFT OR JOURNAL THERETO CONNECTED 18
MADE MORE EVEN, AND THE DISTURBING EFFECT OF DEAD CENTRES ALMOST ENTIRELY
OBVIATED," to be as follows:-
My Invention has relation to means for communicating motion to
shafts and other axles, and it consists in the construction and novel
arrangement of a double crank.
The object of the Invention is to equalize and render uniform the
motion of the shaft or journal connected with the crank and to obviate
practically the disturbing effect of the dead centre. The crank arms
of the ordinary half crank are distant from each other by angular
measurement one hundred and eighty degrees, and the arms of the
quarter crank by similar measurement are distant from each other ninety
degrees. My Invention places the arms of the double crank at a

page_text: distance from each other of one hundred and twenty degrees. Or the
two wrists of the double crank to which the pitman heads are attached
have their position coincident with two of the apices of an equilateral
Instead
triangle whose centre coincides with the centre of the shaft.
of carrying the arms of the double crank directly out from the shaft
I sometimes prefer to extend them parallel with each other for a certain
distance, and then turning outward respectively on opposite sides of the
In order to
shaft until the proper position for the wrists is obtained.
construct this form of my double crank the shaft is bent or shaped so
as to form parallel arms, which, for convenience of description, may
be conceived as turned vertically upward. From the upper ends of
these arms extend outward and downward in opposite directions other
arms lying in a plane perpendicular to the shaft. The outer arms make
with the inner angles of sixty degrees. The outer arms turn at their
ends and running parallel with the shaft for a sufficient distance to
admit of the connection of the pitman heads bend again and running
upward and inward parallel with the said outer arms join, making an
angle of one hundred and twenty degrees with each other, or the same
angle which would have been included between the arms if they had
been extended directly out from the shaft to the wrists. This form of
my double crank enables me to take advantage of the spring of the
metal where advisable. The connecting rods or pitman are pivoted to a
lever respectively above and below its fulcrum and are connected with
wrists. These rods are pivotted at about equal distances from the
fulcrum and they are about the same length. The proper lengths of
the pitman and lever and their angular relations with reference to each
other and to the double crank may be accurately derived by experiment
with the double crank or determined by mathematical rule. When the
crank is pendant in its position the lower pitman is joined to the wrist
nearest the operating lever and the upper pitman to the wrist farthest
therefrom.