An Improvement in Beam Compasses.
Year: 1898

page_text: Date of Application, 25th May, 1898
1000
2000
An Improvement in Beam Compasses.
I, ALPHONSUS JOSEPH BULL, of 29, St. Paul's Road, Canonbury, London, N.,
Mathematical Instrument Maker, do hereby declare the nature of this invention
to be as follows:-
"
This invention relates to the screw adjustment of beam compasses and has for
object to prevent the "shake and consequent inaccuracy which frequently result
from the wear caused by the leg-carrying nut and slide working to and fro upon
the adjusting screw and guides.
According to my invention the nut which works upon the fine adjusting screw
and which carries the adjustable leg of the instrument is combined with a slide
working upon a guide bar mounted on the head or clamp which is fixed on the
bar or rule in the ordinary way, the guide bar being parallel to the adjusting screw
and at such a distance therefrom in the plane of the leg and above or below the
screw as to ensure the required stability. The guide bar may be of any form in
cross section but is preferably tri-lateral or quadri-lateral and the slide which
works upon it may be provided with an adjustable wedge or other means of taking
up wear of the slide and guide bar.
In order to indicate the amount of adjustment made, a scale may be engraved
upon the clamping head to which an index mark on the nut or slide may refer,
and the head of the adjusting screw may be divided like a micrometer screw to
serve as a scale referable to an index mark on the clamp, for still finer divisions.
A. M. & WM. CLARK,
Chartered Patent Agents, 53, Chancery Lane, London.
An Improvement in Beam Compasses.
I, ALPHONSUS JOSEPH BULL, of 29, St. Paul's Road, Canonbury, London, N.,
Mathematical Instrument Maker, 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:-
This invention relates to the screw adjustment of beam compasses and has for
object to prevent the "shake" of the leg and consequent inaccuracy of the instru-
ment, consequent on the wear caused by the leg-carrying and adjusting slide
working to and fro upon the adjusting screw and guides.
According to my invention the slide through which as a nut works the fine
adjusting screw and which carries the adjustable leg of the instrument is also
adapted to work accurately with sliding friction upon a guide bar parallel to the

page_text: adjusting screw and at such a distance therefrom in the plane of the leg (above
or below the screw) as to ensure the required stability. The guide bar may be
of any form in cross-section but is preferably tri-lateral or quadri-lateral and it
is fixed between the limbs of the head or clamp in which the adjusting screw is
mounted to revolve the said head or clamp being fixed on the bar or rule in the
ordinary way.
In order to indicate the amount of adjustment made, a scale may be engraved
upon the clamping head to which an index mark on the nut or slide may refer,
and the head of the adjusting screw may be divided like a micrometer screw to
serve as a scale referable to an index mark on the clamp for still finer divisions.
In the accompanying drawings forming part of this specification Figure 1 is
a face view of the leg-carrying clamp or head shewing the leg-adjusting screw
and guide bar. Figure 2 is a cross-section of the same." The same letters denote
like parts in both figures.
a is the clamp or head adapted to embrace a rule, or beam and to be rigidly
secured thereto by a clamping plate b pressed up by a screw as usual. c is the
fine adjusting screw journalled between collars so as to turn in bearings in limbs
or lugs dd of the head a without being capable of longitudinal motion and pro-
vided with a milled heade for turning it. f is the leg-carrying slide-block
traversed by the screw c which works therein as in a nut, the block being pre-
vented from turning so as to be caused to travel along the screw between the
lugs d.
g is the guide bar for the slide fixed between the lugs d parallel to and
below the screw cupon which the block f is fitted to slide, the bar being pre-
ferably of equilateral triangular section and passing through a hole of corre-
sponding form in the block which is fitted accurately to bear upon all three faces
of the guide bar in such a manner as to present bearing surfaces both on the upper
and under sides and sufficiently extended in the direction of the motion to avoid
appreciable wear of the surfaces in sliding contact and prevent all liability to
shake consequent on the unavoidable wear of the screw in its socket. The bar g
may be fixed in position by being inserted through holes of a form corresponding
to its sectional shape made through the limbs d wherein it is brazed after the parts
are mounted in position. Or it may be otherwise fixed, and it serves not only to
prevent shake of the leg in longitudinal direction of the beam but it also affords
the abutment necessary in the lateral direction necessary to prevent the block f
turning with the screw, so that the engagement of the head of the block with the
under surface of the clamp a is unnecessary. The bar g being thus separately made
and fitted and being secured after the block and screw have been mounted in
position, enables a very accurate fit of the parts to be made.
It will be obvious that the relative positions of the screw and guide bar might
be interchanged without affecting the result. The leg of the instrument is
removably mounted in the slide-block f and is secured by a set screw or other
suitable means as usual.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is:-
In a beam compass the combination with the leg carrying slide block working
as a nut on the fine adjustment screw, of a guide bar fixed parallel to the adjust-
ment screw and on which the leg carrying block is fitted to slide substantially in
the manner and for the purpose specified.
A. M. & WM. CLARK,
Chartered Patent Agents, 53, Chancery Lane, London.