Improvements in Tribrach Arrangements for Instruments of Precision.
Year: 1892

page_text: Date of Application, 18th Aug., 1892
Complete Specification Left, 18th May, 1893-Accepted, 24th June, 1893
PROVISIONAL SPECIFICATION.
Improvements in Tribrach Arrangements for Instruments of
Precision.
WILLIAM FORD STANLEY of 4 & 5 Great Turnstile Holborn London, Optician
do hereby declare the nature of this invention to be as follows:-
The object of my invention is to construct a locking plate for tribrach adjust-
ment which shall obviate the necessity of using the covering spring plate now used
in all forms of tribrach arrangements for holding down the adjusting screws in
theodolites, tacheometers, levels, plane tables and other instruments of precision.
The spring plate being necessarily a weak part in the former construction, liable
to bend away or break and allow the instrument to fall when it is carried over the
shoulder supported only upon its tripod. To carry out my invention I construct
my tribrach locking plate as follows.
The tribrach, that is the three arms which carry the ball ends of the adjusting
screws, are made in section slightly deeper than heretofore. From the extremity
of each arm of the tribrach a hole is drilled longitudinally right through to the
centre of the instrument. This hole is exactly of the diameter of the ball end of the
adjusting screw which is inserted in it. A part of the upper part of this longitudinal
hole is cut away sufficient to admit of the neck of the ball of the milled head
adjusting screw. The opening thereby formed by the cut is bevelled outwards
slightly to allow the adjusting screw to rock within sufficient limits for adjustment.
The balls of the adjusting screws are placed in their positions in my locking plate
before they are screwed into the tribrach which carries the centre of the instrument.
By this means it will thus be seen that it is impossible for anything to break away
by this construction as the whole of the locking plate is in one solid piece.
There is also much less wear upon the balls as they have a bearing surface all
round the hole instead of on two narrow surfaces only as heretofore.
Various modifications may be made, the longitudinal holes may be carried the
up
arms only a sufficient distance for the balls of the parallel screws to enter, but I
preferably carry these holes right through to the centre so that any dust or grit
that may accumulate may be blown through to preserve the fittings from wear.
Any suitable materials may be used.
Dated this 17th day of August 1892.
COMPLETE SPECIFICATION.
Improvements in Tribrach Arrangements for Instruments of
Precision.
WILLIAM FORD STANLEY 4 & 5 Great Turnstile, Holborn, London, Optician
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 object of my invention is to construct a tribruch adjustment which shall
obviate the necessity of using the covering spring plate (locking plate) now used
in all forms of tribrach arrangements for holding down the adjusting screws in
theodolites, tacheometers, levels, plane tables and other instruments of precision.
The spring plate being necessarily a weak part in the former construction, liable
to bend away or break and allow the instrument to fall when it is carried over the
shoulder supported only upon its tripod.

page_text: To carry out my invention I construct my tribrach locking plate as follows:-
The tribrach, that is, the three arms which carry the ball ends of the adjusting
screws are made in section slightly deeper than heretofore. From the extremity of
each arm of the tribrach a hole is drilled longitudinally through towards the centre
of the instrument. This hole is exactly of the diameter of the ball end of the
adjusting screw which is inserted into it. A part of the upper part of this
longitudinal hole is cut away sufficient to admit of the neck of the ball of the
milled head adjusting screw. The opening thereby formed by the cut is bevelled
outwards slightly to allow the adjusting screw to rock within sufficient limits for
adjustment. The balls of the adjusting screws are placed in their positions in the
arms before they are screwed into the tribrach which carries the centre of the
instrument. By this means it will be seen that it is impossible for anything to
break away by this construction or a part to be lost as the whole of the tribrach
is in one piece or pieces fixed together equivalent to this. There is much less wear
upon the balls as they have a bearing surface all round the hole instead of on two
narrow surfaces only as heretofore.
up
the
Various modifications may be made the longitudinal holes may be carried
arms only a sufficient distance for the balls of the parallel screws to enter, but I
preferably carry these holes through to the centre so that any dust or grit that may
accumulate may be blown through to preserve the fittings from wear.
material may be used.
In the accompanying drawings
Any suitable
Fig. 1 represents a plan of my improved tribrach. The outside shape of which
may be curved or shaped in any suitable manner.
Fig. 2 is a longitudinal section of one of the arms shewing the hole, which
carries the ball end of the adjusting screw, carried right through the arm to the
centre.
Fig. 3 is a similar section to Fig. 2 but with longitudinal hole carried only
through a sufficient distance to take the ball end of adjusting screw and allow the
necessary movement.
Fig. 4 is a similar section to Fig. 3 but has the dead metal on the under side of
the arm cleared away for lightness.
Fig. 5 is an end view of one of the arms with round hole fitting ball of adjusting
screw.
Fig. 6 is a similar view to Fig. 5 but with hole squared at bottom.
Similar letters denote corresponding parts throughout the drawings.
A A A are the arms of the locking plate, B B B longitudinal holes through
arms to receive ball ends of adjusting screws, CCC centre of plate screwed to fit
tripod stand top, D D D adjusting screws, E E E feet of tribrach for use when
required to stand on masonry or the like, F F upper tribrach arms of instrument.
Having now fully described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1. The use in combination with theodolites, tacheometers levels, plane tables and
other instruments of precision of a tribrach made solid without moveable spring
plate or holding spring as heretofore.
2. The improved tribrach substantially as herein described and illustrated in the
accompanying drawings.
H. T. TALLACK,
10, Great Turnstile, Holborn, London, W.C., Agent for Applicant,