IMPROVEMENTS IN STEAM ENGINES
Year: 1869

page_text: LETTERS PATENT to John Leechman, of No. 18, Anglesea Villas,
Hammersmith, in the County of Middlesex, for the Invention of
"IMPROVEMENTS IN STEAM ENGINES."-A Communication from abroad
Sealed the 25th September, 1869, and dated the 13th April 1869.
PROVISIONAL SPECIFICATION left by the said John Leechman at the
Office of the Commissioners of Patents, with his Petition, on the
13th April 1869.
I, JOHN LEECHMAN, of No. 18, Anglesea Villas, Hammersmith, in
the County of Middlesex, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN STEAM ENGINES," to be as follows:-
This Invention has for its object improvements in steam engines. In
steam engines as at present constructed the rectilinear motion of the
piston is usually changed into a circular motion on the main shaft by
means of the connecting rod and crank of the engine. This means of
transposing the motion from the rectilinear to the circular has many
well known disadvantages, such, for example, as the irregularity of

page_text: motion of either the piston in the cylinder or the revolving main shaft,
and these disadvantages are greater or less just according to the shortness
or length of the connecting rod, or, in fact, to the room occupied by the
engine.
I employ the following arrangement which seems to avoid the disadvan-
tages of the existing arrangement of connecting rod and crank and pos-
sesses many advantages of its own. My arrangement of machinery may
be described as follows:-The main shaft of the engine is fixed in any
convenient way parallel to the centre line of the cylinder of the engine.
To the cross head working on the motion bars a bush or nut is fixed in
some convenient way so that it may encircle or work on the main shaft
and
I convey, say, the forward motion of the piston in the cylinder to the
main shaft by a pin or pins working on or into a right-hand screw
thread turning the main shaft, say, one-half of its revolution; the
remaining half revolution in the same direction is given in continuation
by the backward motion of the piston in the cylinder conveyed also
through the nut pin or pins attached to the cross head by a left-hand
screw thread, and thus bringing the whole gearing back to the original
starting point ready to proceed again as described above. The dead
points of this style of motion are similar to those of the old arrange-
ment and can be overcome by the same means, namely, by a fly wheel
in a one-cylinder engine, and in a double-cylinder engine by the pistons
of the two engines being at different points of the stroke. It will be
seen that the main shaft of the engine can by this new arrangement be
made to revolve, either more or less or exactly one revolution for the
forward and backward motion of the piston in the cylinder without the
aid of any intermediate machinery. The circular motion of the main
shaft of an engine driven by this new means will progress regularly with
the forward and backward motion of the piston part of one for part of
the other.
An engine constructed after this new plan will occupy much less
space than those as at present constructed, and will not be dependent on
space for regularity of motion.
This new arrangement has special advantages for engines used for
propelling screw steamers.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said John Leechman in the Great Seal Patent Office
on the 13th October 1869.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
LEECHMAN, of No. 18, Anglesea Villas, Hammersmith, in the County of
Middlesex, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Thirteenth day of April, in the year of our
Lord One thousand eight hundred and sixty-nine, in the thirty-second
year of Her reign, did, for Herself, Her heirs and successors, give and
grant unto me, the said John Leechman, Her special licence that I,
the said John Leechman, my executors, administrators, and assigns,
or such others as I, the said John Leechman, my executors, adminis-
trators, and assigns, should at any time agree with, and no others, from
time to time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the
United Kingdom of Great Britain and Ireland, the Channel Islands, and
Isle of Man, an Invention for "IMPROVEMENTS IN STEAM ENGINES," a
communication to me from abroad by William Carey Leechman, of
Colombo, in the Island of Ceylon, upon the condition (amongst others)
that I, the said John Leechman, my executors or administrators, by
an instrument in writing under my, or their, or one of their hands and
seals, should particularly describe and ascertain the nature of the said
Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within six
calendar months next and immediately after the date of the said Letters
Patent.
NOW KNOW YE, that I, the said John Leechman, do hereby declare
the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the
following statement thereof, that is to say :-
This Invention has for its object improvements in steam engines.
In steam engines as at present constructed the rectilinear motion of the
piston is usually changed into a circular motion on the main shaft by
means of the connecting rod and crank of the engine. This means of
transposing the motion from the rectilinear to the circular has many
well-known disadvantages, such, for example, as the irregularity of

page_text: motion of either the piston in the cylinder or the revolving main shaft,
and these disadvantages are greater or less just according to the short-
ness or length of the connecting rod, or, in fact, to the room occupied
by the engine.
I employ the following arrangement, which seems to avoid the dis-
advantages of the existing arrangement of connecting rod and crank, and
possesses many advantages of its own. My arrangement of machinery
may be described as follows:-The main shaft of the engine is fixed in
any convenient way parallel to the centre line of the cylinder of the
engine. To the cross head working on the motion bars a bush or nut is
fixed in some convenient way, so that it may encircle or work on the
main shaft and convey, say, the forward motion of the piston in the
cylinder to the main shaft by a pin or pins working on or into a right-
hand screw thread turning the main shaft say one half of its revolution;
the remaining half revolution in the same direction is given in con-
tinuation by the backward motion of the piston in the cylinder, conveyed
also through the nut pin or pins attached to the cross head by a left-
hand screw thread, and thus bringing the whole gearing back to the
original starting point ready to proceed again, as described above. The
dead points of this style of motion are similar to those of the old
arrangement, and can be overcome by the same means, namely, by a
fly wheel in a one-cylinder engine and in a double-cylinder engine by the
pistons of the two engines being at different points of the stroke. It
will be seen that the main shaft of the engine can by this new arrange-
ment be made to revolve either more or less or exactly one revolution
for the forward and backward motion of the piston in the cylinder
without the aid of any intermediate machinery.
The annexed diagram A if lapped around a cylindrical shaft of a suitable
size would represent on the shaft the form of groove required in order that
the shaft may make one revolution for each complete stroke of the piston.
The diagram B would similarly represent the form of groove required
in order that that the shaft may make one-third of a revolution for each
complete stroke of the piston. The pin of the nut may slide in the
groove and be of the form shown at a in this diagram, or the friction
may be lessened by the pin of the nut being made to consist of a pin
in which a wheel or pulley works in the groove in the shaft, as in the
diagram C; and in order to avoid a blow at each end of the stroke the
ends of the grooves in the main shaft may be curved, as in the diagram D

page_text: The circular motion of the main shaft of an engine driven by this new
means will progress regularly with the forward and backward motion of
the piston part of one for part of the other.
An engine constructed after this new plan will occupy much less space
than those as at present constructed, and will not be dependent on space
for regularity of motion..
This new arrangement has special advantages for engines used for
propelling screw steamers.
In witness whereof, I, the said John Leechman, have hereunto
set my band and seal, this Thirteenth day of October, in
the year of our Lord One thousand eight hundred and sixty-
nine.