IMPROVEMENTS IN THE CONSTRUCTION OF CRANK SHAFTS FOR SCREW STEAMERS
Year: 1882

page_text: LETTERS PATENT to David Purves of 45 Rushmore Road Lower Clapton,
in the County of Middlesex, Engineer for an Invention of IMPROVEMENTS
IN THE CONSTRUCTION OF CRANK SHAFTS FOR SCREW STEAMERS
PROVISIONAL SPECIFICATION left by the said David Purves at the Office
of the Commissioners of Patents on the 20th July 1882.
DAVID PURVES of 45 Rushmore Road Lower Clapton in the County of
Middlesex Engineer "IMPROVEMENTS IN THE CONSTRUCTION OF CRANK SHAFTS
FOR SCREW STEAMERS
"
The crank shafts of screw steamers are subject to severe local straining when
the bearings by wear or from any other cause become not truly fair and sometimes
fracture and total break-down result. Now my invention is designed to obviate
such evils by enabling the shaft to yield a little to accomodate the unfairness of
bearings. For this purpose I make crank shafts in pieces put together in such
manner as will allow of the required small yielding without producing fracture.
In carrying out my invention according to one arrangement I join the two portions
of a crank shaft by recessing the forward crank web and fitting the end of the crank
pin into the recess the end of the crank pin abutting on the bottom of the recess or
on a washer, the two pieces are then bolted firmly together by means of one bolt
passing longitudinally through the crank pin and the webs The recess fitting and
long bolt admit of the slight amount of alteration of form which would otherwise
take place by overstraining the solid shaft.
The after end of the crank pin may be forged or cast solid with the after web or
it may be fitted into a bored out eye in the web and secured with a nut
According to another arrangement I fit a separate crank pin or forge or cast the
crank pin in one piece with the after web and extending to the forward side of the
forward web but not in a piece with it. I form the forward end of this crank pin
with a face oblique with the centre line of the crank which face fits a face on the
FD

page_text: forward web the two being connected by a transverse bolt that passes through the
oblique face of the crank pin and through the forward web.
The two pieces of the shaft can to a small extent alter their relative positions
about this bolt attachment and so accomodate the shaft to the want of fairness
or to undue slackness of the bearings. Between the end of the crank pin and web
faces I fit a strong washer to partly or wholly relieve the bolt of shearing stress.
I have by way of examples described the arrangements of parts as for the
forward web and the after web respectively and I prefer having them as described
but the construction for the after web may in some cases be substituted for the
forward web and vice versa and instead of one transverse bolt as described there
may be two bolts.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said David Purves in the Great Seal Patent Office on the 17th January
1883.
DAVID PURVES late of 45 Rushmore Road, Lower Clapton, in the County of
Middlesex, Engineer, now residing at Azalea Lodge, East Dulwich Grove, Champion
Park South, in the County of Surrey, "IMPROVEMENTS IN THE CONSTRUCTION OF
CRANK SHAFTS FOR SCREW STEAMERS
"
The crank shafts of screw steamers are subject to severe local straining when
the bearings by wear or from any other cause become not truly fair and some-
times fracture and total break-down result. Now my invention is designed to
obviate such evils by enabling the shaft to yield a little to accomodate the
unfairness of bearings.
For this purpose
I make crank shafts in pieces put together in such manner as
will allow of the required small yielding without producing fracture.
In carrying out my invention according to one arrangement I join the two
portions of a crank shaft by recessing the forward crank web and fitting the end
of the crank pin into the recess, the end of the crank pin abutting in the recess;
the two pieces are then bolted firmly together by means of one bolt passing longi-
tudinally through the crank pin and the webs. The recess fitting and long bolt
admit of the slight amount of alteration of form which would otherwise take place
by over straining the solid shaft.
Figs. 1 and 1a of the accompanying drawings shew in side view and end
elevation respectively, such an arrangement of crank shaft.
a is the forward crank web recessed as shewn at a¹ to receive the end of the
crank pin 6 which abuts in this recess.
The two pieces are then bolted together by means of one bolt & which passes
longitudinally through the crank pin b and the webs c and a and is held in place
by a nut d'.
The after end of the crank pin instead of being forged or cast solid with the
after web as in the above example may be fitted into a bored out eye in the web
and secured with a nut.
Figs. 2 and 2a illustrate an arrangement wherein the crank pin b is made
separate from the after web c and is secured by a nut e.
Figs. 3 and 3 .shew a modification in which the crank pin b instead of being
secured in the after web c by a nut is fitted into a bored out eye in the web c, and
the web is shrunk on to it.
Figs. 4 & 4a shew, by views similar to the foregoing, an arrangement in which
the crank pin 6 (in this case formed in one piece with the after web c) itself
extends through the forward web a, its diameter as shewn at 6¹, being reduced
from the bottom of the recess.
A nut d¹ serves to hold the parts in position. It will be seen that in this
arrangement the bolt d is dispensed with, I however prefer a bolt d as described
above, as being more reliable."
According to another arrangement I fit a separate crank pin or forge or cast the
crank pin in one piece with the after web and extending to the forward side of the
forward web but not in a piece with it.
I form the forward end of this crank pin with a face oblique with the centre
line of the crank which face fits a face on the forward web the two being connected
by a transverse bolt that passes through the oblique face of the crank pin and
through the forward web.

page_text: The two pieces of the shaft can to a small extent alter their relative positions
about this bolt attachment and so accomodate the shaft to the want of fairness
or to undue slackness of the bearings.
Referring to Figs. 5 and 5a the crank pin b extends to the forward side of the
forward web a but is not in a piece with the forward web.
The forward end of the crank pin is formed with a face oblique with the centre
line of the crank to fit a face on the side of the forward web a.
f is a transverse bolt passed through the oblique face of the crank,pin band
through the forward web a.
As in the former cases the after end of the crank pin may be either solid with
the after web c or it may be fitted into a bored out eye and fixed into the web by
shrinking or it may be secured by a nut.
Between the face of the end of the crank pin and web, I fit a strong washer g to
partly or wholly relieve the bolt of shearing stress.
I have by way of examples described the arrangements of parts as for the
forward web and the after web respectively, and I prefer having them as described,
but the construction for the after web may be in some cases substituted for the,
forward web and vice versa, and instead of one transverse bolt as described there.
may be two bolts.
The bolt connections through the crank pin and forward web admit of a
sufficient amount of yielding to practically relieve the journals of undue stress and
at the same time the connection is strong enough for transmitting the engine
power to the propellor shafting and much of the local straining that brings about
rupture in solid and rigid shafts is in this way allowed for by construction.
Having thus described the nature of my said invention and the manner of
performing it, what I claim is,
1. In a screw steamer the use of a crank shaft (for driving the screw propellor)
wherein the crank pin is solid with or rigidly fixed in one crank web, fits abuttingly
into a recess in the other crank web, and is held to the abutment by a through
bolt and nut substantially as described and for the purpose set forth.
2. The modification substantially as described with reference to Figs. 4 and 4ª.
3. In a screw steamer the use of a crank shaft (for driving the screw propellor)
wherein the crank pin is solid with or rigidly fixed in one crank web and is con-
nected with the other crank web a by a transverse bolt (or bolts) substantially a
described with reference to Figs. 5 and 5° and for the purpose set forth.
In Witness whereof I the said David Purves have hereunto set my hand
and seal this seventeenth day of January in the year of our Lord, one
thousand eight hundred and eighty three.
DAVID TURVES.
(L.S.)
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