Improvements in Mechanism for Raising and Lowering the Sight Bars of Guns or for Moving other Bars Endwise.
Year: 1887

page_text: Date of Application, 3rd Mar., 1887
Complete Left, 2nd Dec., 1887
Complete Accepted, 13th Jan., 1888
Improvements in Mechanism for Raising and Lowering the Sight
Bars of Guns or for Moving other Bars Endwise.
I, GEORGE STUART of the Elswick Works Newcastle-on-Tyne, Engineer, do hereby
declare the nature of this invention to be as follows:-
For raising and lowering sight bars I employ a volute or spiral toothed worm of a
conical form made to gear on one side of its axis with a toothed rack cut on the sight
bar. The volute or spiral tooth or groove is cut upon the face of a disc coned to such
an angle that when the axis of the coned disc is at an angle to the face of the rack one
part of the volute or spiral on one side of the axis may be in gear with the rack
whilst the part of the volute or spiral on the opposite side of the axis is out of gear
with the rack. The teeth of the rack are cut with a volute cutter of exactly the same
form and pitch as the conical volute worm that has to actuate the bar or rack. The
spindle or axis of the spiral toothed worm may be provided with a milled head by
which it can be turned.
The spiral toothed worm may be acted upon by a spring at the back to keep it
pressed towards and in gear with the rack but yet allow of the spindle being drawn
back by its milled head or by a lever or in other ways so as to hold the worm back
out of gear and allow the bar to be then moved freely endwise.
Dated this 3rd day of March 1887

page_text: Figure 3 is also a section but the volute or spiral is here shown drawn back out of
gear with the rack.
Figures show parts separately, viz. the milled head; the axis or spindle
with its coned disc, and volute or spiral tooth; the coiled spring and the cap which
retains the spindle and spring in place.
Figure 5 is a section and shows another form of the mechanism.
a is the sight bar it has teeth a' cut upon it and it is held in a socket 6 in which
it is capable of sliding freely up and down. c is the axis or spindle, c¹ is the coned
disc on the end of the spindle and the volute or spiral tooth upon the face of the
coned disc. The disc c is received into a recess in the side of the socket b and it is
there retained by the screw cap d. The spindle is able to turn and to slide freely in
the cap d and the coiled spring e is compressed between the cap and the coned disc c.
The spring presses the disc forward towards the side bar. In consequence of the

page_text: form given to the disc c¹ and the obliquity of the spindle c the tooth c gears with the
rack on the sight bar only on the under side of the disc. fis the milled head fixed
upon the spindle.
On turning the spindle the sight bar receives a slow longitudinal motion either up
or down according to the direction in which the milled head is turned. By drawing
back the milled head however the tooth c can be disengaged from the rack teeth a¹
and then the sight bar can be rapidly moved either up or down by hand.
In the modification shown by Figure 5 the cap d is not screwed into its place but
is retained by the pins di d¹ which project from its sides through inclined slots in
the part of the socket a which receives the cap. One of these pins is provided with
a knob or handle and by this the cap can be turned; it is thereby caused to advance
towards or recede from the rack. The cap when so moved carries the spindle with
it and puts the volute or spiral tooth into gear with the rack or withdraws it as the
case may be.
The great advantage of this mechanism consists in the secure and firm hold with
which the sight bar is retained in position it is not dependent on the friction of the
sight bar in the socket but the bar is always held by the lower part of the volute or
spiral tooth gearing into the bar.
It is obvious that this mechanism is applicable not only to sight bars but also to
other bars which require to be moved in a longitudinal direction through a socket,
sometimes slowly and accurately and at other times rapidly and which also from
time to time require to be securely and firmly held in position. It is applicable for
example to adjustable supports for telescopes and other scientific instruments.
It is not in all cases requisite that the disc c¹ should be capable of being drawn
back away from the bar.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what I
claim is
1. Mechanism substantially as described for raising and lowering the sight bars
of guns or for moving other bars endwise consisting of the axis or spindle c with
its coned disc c¹ and volute or spiral tooth c³ the said spindle being set obliquely to
the bar with the volute or spiral tooth gearing with teeth upon the bar on one
side only of the axis.
2. In such mechanism mounting the said spindle in such manner that it can be
drawn back away from the teeth upon the bar to admit of the rapid longitudinal
movement of the bar when required.
Dated this 28th day of November 1887.