IMPROVE- MENTS IN SCREW BOLTS
Year: 1862

page_text: LETTERS PATENT to William Palliser, Captain of Her Majesty's 18th
Hussars, of the City of Dublin, Ireland, for the Invention of "IMPROVE-
MENTS IN SCREW BOLTS."
PROVISIONAL SPECIFICATION left by the said William Palliser at
the Office of the Commissioners of Patents, with his Petition, on the
6th December 1862.
I, WILLIAM PALLISER, Captain of Her Majesty's 18th Hussars, of the City
of Dublin, Ireland, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN SCREW BOLTS," to be as follows:-
This Invention consists of certain improvements in screw bolts, the object of
which is that the extention due to any strain may be placed along the shank,
instead of its being as heretofore confined to the screwed part. A peculiarity
exists in iron or metal bars subjected to tensile strain, such that the extension.
due to the stain occurs entirely at the weakest point in the bar; thus in screw
bolts as at present constructed the whole extension takes place in the last
thread of the screw, which thus bears the entire strain.
I propose to form the stem or shank of the bolt slightly smaller in diameter
than the diameter of the bottom of the thread of the screw. The bolt should
be larger at each end than towards the middle portion, in order to fit the bolt
holes.
The advantage of this method is that the extension due to the strain

page_text: will occur throughout the reduced part of the bolt, and not on the thread
The bolt is therefore particularly adapted to resist dynamical
strain.
This improved form of screw bolt, provided with a head and nut, is not only
adapted to the fastening of armour to vessels, but also to all other purposes to
which bolts and nuts ars now applied, especially where great and sudden strains.
are thrown upon the screw threads of the bolts.
In some cases I propose to make the screwed part of the bolt of steel or
other less easily stretched material than the shank, which would accomplish
the same object in a different manner to the arrangement first described.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said William Palliser in the Great Seal Patent Office on
the 6th June 1863.
TO ALL TO WHOM THESE PRESENTS SHALL COME, 1, WILLIAM
PALLISER, Captain of Her Majesty's 18th Hussars, of the City of Dublin; send
greeting.
I
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Sixth day of December, in the year of our Lord
One thousand eight hundred and sixty-two, in the twenty-sixth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said William Palliser, Her special licence, that I, the said William
Palliser, my executors, administrators, and assigns, or such others as I,
the said William Palliser, my executors, administrators, 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 SCREW BOLTS," upon the condition (amongst others) that I,
the said William Palliser, 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 William Palliser, do hereby declare
the nature of my said Invention, and in what manner the same is to be

page_text: performed, to be particularly described and ascertained in and by the
following statement :-
It will be necessary, in order the more clearly to define the nature of this
Invention, in the first place. to describe the cause of the nuts flying-off the
screw bolts, by means of which the armour plates are attached to their backing..
The plate on being struck by a shot bends in more or less at the point of
impact, while the surrounding portions spring quickly forwards, and thereby
bring a sudden impulsive strain to bear on the bolts. Owing to the great
weight of the armour plate, thus suddenly set in motion, the bolts must yield to
this shock, and either stretch slightly or else break. In the ordinary screw bolt
its uniform size is suddenly very much reduced by a deep screw thread running
round and round one end of the shank, the result of which is that the shank of
the bolt is much stronger than the screwed part, and therefore practically
remains rigid when subjected to the impulsive strain, and thus all the stretch
due to this strain is confined to the screwed part. If the nut be screwed right
up to the end of the thread, it will be easily seen that this stretch will become
confined to the last complete turn of the screw thread; thus the distance,.
though relatively short for the whole length of the bolt to stretch through,
becomes very great in comparison with the short part of the bolt (namely,
the width of a screw thread) to which this stretch is confined. The result is
that rupture takes place, and the nut flies off, carrying with it a portion of the
bolt, which is separated by a plane passing through the last complete turn of
the screw thread. The measure of the strength of the bolt to resist an impul
sive strain is the product of the mean resistance it offers while stretching into
the distance through which it can stretch; if therefore this stretch be virtually
confined to the last turn of the screw thread, and if this screw thread be one-
tenth of an inch wide, and further, if the bolt be required to stretch through
one-tenth of an inch, it will follow that the iron at this place would have to
stretch through a space equal to its original length. This, the property of 'the
metal will not admit, and therefore rupture occurs. "If, however, the bolt be
reduced at any part, for any short distance, say one iuch, to the size to which
it is reduced by the screw thread; the iron at this place will only have to střetel
stretch'
through one-tenth of its original length, and since it cau stretch this amount,
the bolt will not break. It will be evident that theoretically the longer
the reduced part the stronger the bolt will become to resist an impulsive strain,
since the distance through which the bolt can stretch is proportional to the
length of the stretching part. It will also be evident that the reduced part
must be cylindrical, or of equal strength throughout, for if it be made weaker
at any part than elsewhere, the stretch will occur at this place, and the object'
:
人:

page_text: of reducing the bolt will be lost. It is however found that screw bolts do not
always break off at the screwed part, but that some of them break off at the
head. The cause of this is owing to the manner in which the head is formed,
namely, by heating the bolt and striking. it on the end, and thereby enlarging or
upsetting the iron at-this place. The result is, that the grain of the iron, which
before ran longitudinally or in the direction of the strain, is caused to lie trans-
versely or at right angles to this strain, as shewn at Fig. 1. This circumstance,
although it does not much affect the strength of the iron to resist a gradual or.
statical strain, greatly weakens it when subjected to an impulsive one, so much
so that sometimes it makes the bolt weaker at this point than it is at the part
where it is reduced by the screw thread, and hence the head breaks off.
I propose in the first place to reduce the shank of the bolt cylindrically,
either in part or throughout its entire length to the size to which the end is
reduced by the screw thread. Instead of this, if it be desirable to do so, I can
reduce the bolt in part either about the middle or towards either end. And
supposing it be required that the bolt should thoroughly fill the bolt hole, I
can cast zinc or other metal or alloy round the reduced part, and thereby
make the bolt of uniform size throughout.
In order to diminish as much as possible the amount by which it is neces-
sary that the shank of the bolt should be reduced, I propose making the screw
thread much shallower and finer than those in general use. I also prefer that
this thread should be of a rounded form, to obviate any tendency there.
might be in a sharp thread to cause the nut to tear off the end of the bolt.
Instead of reducing the shank of the bolt, I can satisfy the conditions above
enumerated, by forming the screwed part of the bolt of shear steel or other
weldable steel which I can weld on to the iron bolt, in the form of the splice
of a fishing rod, as represented in Fig. 4 of the accompanying Sheet of
Drawings, and I may increase the strength of the steel by tempering it.
In the second place I form the head of the bolt by rolling or otherwise
drawing down the bolt from a bar of iron sufficiently thick to leave the head
on the bolt, by means of which the grain of the iron will run in a longitudinal
direction, as shewn at Fig. 2.
I do not limit myself to this form of bolt as applied to iron only, but I claim
it for all bolts which are subjected to impulsive strains, whether made of steel,
copper, or other substance.
Fig. 2 shews a bolt reduced throughout; Fig. 3 shews a bolt reduced at
any part.
Having now described the nature of my said Invention, and the manner in
which the same is to be performed, I would remark in conclusion that I do not

page_text: restrict myself to the precise details and configuration of parts described, as the
same may obviously be modified or varied, without in any way departing from
the principles on which my Invention is based, but what I claim and desire
to be secured to me by the herein in part recited Letters Patent are the
"Improvements in Screw Bolts," substantially in the manner herein specified
and illustrated by the Drawings annexed.
In witness whereof, I, the said William Palliser, have hereunto.set my
hand and seal, this Third day of June, in the year of our Lord
One thousand eight hundred and sixty-three.
Witness,
ALEX. PRINCE,
Office for Patents,
4, Trafalgar Square,
Charing Cross.
W. PALLISER. (L.S.)