An Improvement in Breech Screws for Ordnance.
Year: 1899

page_text: PROVISIONAL SPECIFICATION.
An Improvement in Breech Screws for Ordnance.
I, ARTHUR TREVOR DAWSON, of No. 28, Victoria Street, Westminster, in the
County of London, Superintendent of Ordnance Works, do hereby declare the
nature of this invention to be as follows:-
1
The breech plug and internal screw for closing the breech of a gun are made
with arcs of the thread cut away, so that it requires only a partial turn of the
plug to lock it in position and to unlock it.
In order to lessen the extent of turn required for this purpose and consequently
the gap between the threaded arcs, these arcs are made in steps of different
radius, and thus there is a larger extent of thread engaged when the plug
locked in position.
It is however difficult to make the screw threads in steps, and between the
steps notches have generally to be cut for clearance of the tool employed to
cut the threads.
In order to facilitate the execution of the work, the thread, instead of being
made in steps, is sometimes made as a spiral arc, of radius gradually diminish-
ing from one end of each threaded arc to the other. This form which can be
easily produced by a milling operation is however objectionable because if the
plug is not turned quite home, the threads are not engaged to their full depth,
and consequently when the threads are of V section, which is preferred for
the sake of strength, the plug, when not screwed fully home, is in a loose
shaky condition.
My invention relates to the formation of the screw thread of the breech
and plug in such a way that while it can be made as easily as the spiral thread,
it provides against looseness and shake of the plug when it is not screwed
fully home. For this purpose, instead of making the whole extent of the
threaded arc a spiral curve, I make part of it of the greatest radius truly
circular, and the rest of it spiral, the circular portion being eased into the spiral
without any abrupt break of the general curvature. This particular form of
thread can be easily produced by a milling operation, and it presents the advan-
tage that even when the plug is not screwed quite home, there is no looseness
or shake, as the portions of thread which are of circular curvature still remain
engaged to their full depth.
Screws formed in the manner described may be tapered so that the plug
requires no longitudinal motion to clear the threads of the breech when it is
Bwung in or out on its carrier.
T: 01
Ta 1000

page_text: —
I, ARTHUR TREVOR DAWSON, of No. 28, Victoria Street, Westminster, in the
County of London, Superintendent of Ordnance Works, 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 breech plug and internal screw for closing the breech of a gun are made
with arcs of the thread cut away, so that it requires only a partial turn of the
plug to lock it in position and to unlock it.
In order to lessen the extent of turn required for this purpose and consequently
the gap between the threaded arcs, these arcs are made in steps of different radius,
and thus there is a larger extent of thread engaged when the plug is looked in
position, than there would be, if all the steps had the same radius.
It is however difficult to make the screw threads in steps, and between the
steps notches have generally to be cut for clearance of the tool employed to
cut the threads.
In order to facilitate the execution of the work, the thread, instead of being
made in steps, is sometimes made as a spiral arc, of radius gradually diminish-
ing from one end of each threaded arc to the other. This form, which can bo
easily produced by a milling operation, is however objectionable because if the
plug is not turned quite home, the threads are not engaged to their full depth,
and consequently, when the threads are of V section, which is preferred for
the sake of strength, the plug, when not screwed fully home, is in a loose
shaky condition.
My invention relates to the formation of the screw thread of the breech
and plug in such a way that, while it can be made as easily as the spiral thread,
it provides against looseness and shake of the plug, when it is not screwed
fully home. For this purpose, instead of making the whole extent of the
threaded are a spiral curve, make part of it of the greatest radius truly
circular and concentric with the axis and the rest of it spiral, the circular
portion being eased into the spiral without any abrupt break of the general
curvature. This particular form of thread can be easily produced by a milling
operation, and it presents the advantage that even when the plug is not screwed
quite home, there is no looseness or shake, as the portions of thread which are
of circular curvature still remain engaged to their full depth.
Screws formed in the manner described may be tapered so that the plug
requires no longitudinal motion to clear the threads of the breech when it is
swung in or out on its carrier.
The accompanying drawings shew breech plugs according to this invention.
Fig. 1 is an end view of a plug having its thread made in two segments.
Fig. 2 is a side view of such plug with parallel sides.
Fig. 3 is a side view of such plug made taper.
Fig. 4 is an end view of a plug having its thread made in three segments,
Figs. 5 and 6 are side views shewing the parallel sided and the taper plug
respectively.
Each segment of the thread consists of an arc of the largest radius from a to b
truly circular and concentric with the axis of the plug, the rest of the segment
from to being of spiral curvature.
It will be seen that if the plug be not screwed quite home, that is to say if a
does not reach d the extremity of the segment of the internal thread of the
breech with which point a should coincide when the plug is screwed home,

page_text: there is still in each segment an arc db circular and concentric in which the
screw threads are engaged to their full depth so that the plug is not loose or
shaky.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
A breech screw for a gun divided into segments each having a curvature, a
portion of which at the greatest radius is circular and concentric with the axis,
the rest being spiral, substantially as and for the purpose set forth.
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ABEL & IMRAY,
Agents for the Applicant.
ABEL & IMRAY,
Agents for the Applicant.