Improvements in or relating to Piston-rods and Cross-heads, and Devices for Connecting them Together.
Year: 1896

page_text: Date of Application, 3rd Mar., 1896-Accepted, 2nd May, 1896
Improvements in or relating to Piston-rods and Cross-heads, and
Devices for Connecting them Together.
A communication from ERNST J. MULLER, of Butte City, Silverbow County,
Montana, United States of America, Mechanical Draughtsman.
1, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
Chartered Patent Agent, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :-
The main objects of this invention are to avoid unduly straining and weakening
the piston rod in connecting it by a key with the cross-head, and to facilitate the
attachment and detachment of the piston rod to and from the cross-head.
It consists essentially of a cross-head having a plain longitudinal bore or straight
hole, a piston rod having one end fitted in said bore, and a transverse key way
through it, a key without taper fitted loosely in said key way and means of forcing
the piston rod and cross-head in opposite directions and holding them in engagement
with opposite edges of said key.
In the accompanying drawing like letters designate the same parts in the several
figures.
Fig. 1 is a longitudinal section on the line 1-1 of Fig. 2 of a cross-head and
piston rod attachment embodying this invention;
Fig. 2 is a plan view; and
Fig. 3 a longitudinal section of the device on the line 3-3 of Fig. 1.
Heretofore it has been customary to secure piston rods which are formed with
tapering ends and key ways for the purpose in tapering bores of the cross-heads by
means of tapering keys, which are driven into place by a hammer. By this means
of attachment the piston rod is frequently strained between the ends of the key way
nearly if not quite to the point of rupture by driving the key into place, the force
employed in the operation being indeterminable and usually excessive, varying of
course, according to the weight of the hammer and the strength and judgment of
the operator.
To avoid the objection to the above explained method of attachment, piston rods
bave been threaded and screwed into the cross-heads, but as the pistons are usually
secured to their opposite ends and placed in their cylinders, before the piston rods
and cross-heads are connected, this method of attachment is objectionable because
it involves turning the pistons in their cylinders, which in the case of a large and
heavy engine or pump, is a laborious and inconvenient operation.
These objections are avoided by this improved means of attachment.
Referring to the drawing, A designates a cross-head having a hub a with a
straight longitudinal bore and an intersecting transverse slot or key way a¹ without
taper. B designates a part of a piston or pump rod, having a reduced end 6 fitted
into the bore of the cross-head, a screw thread on the adjacent unreduced
portion and a straight transverse slot or key way through the reduced end.
C is a straight key loosely fitted in the key ways a' and 6 of the cross-head and
piston rod respectively. D is a nut tapped to fit the screw thread on the
unreduced portion of the piston rod and adapted to be turned thereon against the

page_text: end of the hub a and to force and hold opposite ends of said key ways in engage-
ment with, opposite edges of the key C. It is obvious that by this means the
piston rod and cross bead can be readily connected and disconnected without
turning the piston rod, and that the key can be secured in place with much less
liability of straining and weakening the piston rod than by driving a tapering key
into place, the force applied through a wrench for turning the nut D being
susceptible of much more accurate determination and regulation than the force
applied by the blows of a hammer for driving a tapering key into place.
This improved connection also facilitates the fitting of the piston rod, and
enables ready compensation for variation in the distance between the centres of
the crank pin and cross-head pin, due to taking up wear of the crank pin brasses,
and operation that tends to lengthen or shorten the connecting rod, and thereby
reduce the clearance of the piston in one end of the cylinder and increase it in the
other.
If a mistake is
In building engines according to the usual practice, all parts are made and
finished exactly to given dimensions before they are assembled, with the exception
of the length of the piston rod, the measurement for which in each case is
accurately made after the parts have been assembled. In this way the unavoidable
variation in the distance between the centre of crank pin and cylinder, due to
unequal shrinkage of castings and inaccuracies of workmanship, is taken into
account and provided for in fitting the piston red in the cross head and cutting the
key-way, operations requiring a high grade of skill and workmanship. With this
construction the fitting required to compensate for the variations above noted is
confined to the key, and no more skill is required in fitting the piston rod to the
cross-head nud cutting the key-way therein than in the construction of other parts
of the engine. The key-way being made of sufficient length the measurement for
the key is taken when the parts have been assembled as above explained, from the
outer end of the key way to the opposing face of the cross-head.
made in this measurement or in fitting the key, it is a simple and easy matter to
make another. In fitting the piston rod and making the connection between it and
the cross-bead according to methods usually followed, allowance is frequently made
for the lengthening or shortening of the connecting rod by making the clearance of
the piston at one end of the cylinder greater than at the other. This is obviously
objectionable and tends to unnecessarily increase the clearance space. By this
improved connection the clearance of the piston at both ends of the cylinder may
be made exactly the same at the outset and thus the clearance space can be
reduced to a minimum. This is of especial advantage and importance in gas
compressors designed to produce nud maintain high pressures. As the connecting
rod is lengthened or shortened by taking up wear on the brasses, thus disturbing
the adjustment of the piston, a new key can be easily substituted that will com-
pensate for the variation and maintain the proper adjustment of the piston.
Having now particularly described and ascertained the nature of the said inven
tion as communicated to me by my foreign correspondent and in what manner the
same is to be performed, I declare that what I claim is ;-
1. The combination of a cross-head having a longitudinal bore or hole, a piston
rod having one end fitted into said bure and forined with a transverse key way,
a key without taper loosely fitting said key way, and means applied to said piston
rod of clamping the key between one end of the key way in said rod and an
opposing face of the cross-hend, substantially as and for the purposes set forth.
2. The combination of a cross-head having a straight longitudinal bure or hole,
a piston rod having a reduced end fitted therein and formed with a transverse key
way, a key without taper loosely fitting said key way and a nut threaded on the
unreduced portion of the piston rod and adapted to be screwed thercon against the
cross-head, substantially as and for the purposes set forth.
3. The combination of a cross-head having a straight cylindrical bore and an
intersecting key way a piston rod having a reduced end fitted in said bore and

page_text: formed with a transverse key way a straight key without taper loosely fitting the
key way in said piston rod and a nut threaded on the unreduced portion of said
piston rod and adapted to be screwed thereon against the cross-head substantially
as and for the purposes set forth.
Dated this 3rd day of March 1896
BOULT & WADE,
Agents for the Applicant.