IMPROVEMENTS IN COMPASSES OR DIVIDERS AND CALLIPERS
Year: 1883

page_text: LETTERS PATENT to Alexander Melville Clark of the firm of A. M and
W. Clark of 53 Chancery Lane in the County of Middlesex Fellow of the
Institute of Patent Agents for an Invention of IMPROVEMENTS IN COMPASSES
OR DIVIDERS AND CALLIPERS communicated to him from abroad by Williain
Holland Mitchell; of Boston in the County of Suffolk and State of
Massachusetts, United States of America
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark
at the Office of the Cominissioners of Patents on the 26th June 1883.
ALEXANDER MELVILLE CLARK of the firm of A M and W Clark of 53 Chancery
Lane in the County of Middlesex Fellow of the Institute of Patent Agents
"IMPROVEMENTS IN COMPASSES OR DIVIDERS AND CALLIPERS [communicated to
him from abroad by William Holland Mitchell, of Boston in the County of Suffolk
and State of Massachusetts, United States of America]
"
This Invention relates to now and improved dividers or compasses and callipers
which admit of being set approximately by hand and have devices for accurately
and readily adjusting the distance between the points of the legs.
The legs of the dividers, compasses or callipers instead of being jointed together
by the usual form of joint have cach a disc shaped head provided with an annular
flange and forming a cap the two caps meeting and forming together a hollow
joint or box in which is contained a worm wheel A worm on a short spindle
mounted in one of the legs and turned by wings, gears with this worm wheel. The
pivot of the joint is a bolt having a squared shoulder fitting a hole in the head of
one leg, a tapered shank passing through the worm wheel and a threaded end on
which is screwed a nut which holds the parts together. Over this nut a screw cap
provided with a levor handle and forming a key is screwed on the end of the bolt
and bears against the adjacent disc or head so as when tightened up to lock the
joint firmly.
In order to adjust the compasses this key is loosened and the legs are then set
approximately by hand after which their points are accuratoly adjusted by turning
the worm spindle. The worm wheel with which the latter gears is held by friction
between the heads of the two legs and has one of its faces recessed so that the
friction shall be unequal on its two faces and less on the side corresponding to the
leg in which the worm pinion is mounted so that on turning the latter the motion
will be between its leg and worm wheel the latter then remaining rigid with the
head of the other leg although free to slip when the legs are adjusted by hand

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Melville Clark in the Great Seal Patent Office on the
24th December 1883.
"
ALEXANDER MELVILLE CLARK of the firm of A. M and W. Clark of 53 Chancery
Lane in the County of Middlesex Fellow of the Institute of Patent Agents.
"IMPROVEMENTS IN COMPASSES OR DIVIDERS AND CALLIPERS A communication
to me from abroad by William Holland Mitchell, of Boston in the County of Suffolk
and State of Massachusetts, United States of America.
This Invention relates to new and improved dividers or compasses and callipers
which admit of being set approximately by hand and have devices for accurately
and readily adjusting the distance between the points of the legs.
The Invention is illustrated in the accompanying drawings forming part of this
specification in which similar letters of reference indicate corresponding parts in all
the figures.
Figure 1, is a side view of a pair of the improved dividers or compasses.
Figure 2, is a section in a plane perpendicular to the axis, of the same construction
but provided with calliper legs. Figure 3, is a sectional view of one of the legs.
Figure 4, is an enlarged detail cross sectional elevation of the joint of the same.
Figure 5, is a back view of the joint bolt. Figure 6, is a face view of the nut. The
same letters of reference indicate the same parts in all the figures. A A are the
legs of the dividers, compasses or callipers, each of which is provided at the upper
end with a disc shaped head A¹ or A³, each having an annular flange a forming a
circular cap, the two caps meeting as shown and together forming a hollow joint
or box in which is contained a worm wheel C. The disc A¹ has a round hole b and
the disc A² has a squared' hole d. The worm wheel C is provided on its periphery
with a worm thread and has a central aperture g through which passes a bolt D
provided with a head D' and a tapering shank D³ the free end of which is screw
threaded. The bolt also has a squared shoulder & next the head which fits into the
square hole d. The wheel C is enclosed between the caps A' A' whose flanges a
meet together and the bolt D is passed through the three parts A¹ A² and C and
receives a nut E on its threaded ond which holds the parts together. This nut
has a shoulder E³, which fits in a recess around the hole b. F is a cap screwing on
the threaded end of the bolt D recessed at F¹ to enclose the nut E and bearing
against the head A'. This cap is provided with a lever handle F and forms a key
by which when tightened up the joint is firmly locked. G is a spindle mounted in
the leg corresponding to the head A', and having on its inner end a worm J which
is situated between the legs and partly received in a recess K in the one leg, and
partly in a corresponding recess in the other leg, when they are closed together.
The outer end of the spindle has fastened to it a winged head H by which the
spindle is turned. The worm J gears with the worm wheel C which has one face
made flat and the other recessed at h leaving a raised external rim so that the
friction surface of the recessed face will be less than on the opposite side.
In order to adjust the compasses, the key F is loosened and the legs are then set
approximately by hand after which their points are accurately adjusted by turning
the worm spindle G. The worm wheel C with which the worm J gears is held by
friction between the heads A' A' of the two legs, and as one of its faces is recessed
at h the friction is unequal on its two faces, and less on the side next A' which
corresponds to the leg in which the worm spindle G is mounted. Consequently on
turning the worm Jit will travel around the worm wheel the motion being
between the head A³ and the worm wheel, the latter then remaining rigid with the

page_text: head A¹ of the other leg. But when the legs are adjusted by hand the head A¹
slips on the worm wheel C.
Having described the nature of the said Invention and the manner of performing
the same, I declare that what I claim as the Invention to be protected by the
hereinbefore in part recited Letters Patent is:
1 A pair of compasses, dividers or callipers, having a worm wheel in the joint
and a worm held in one shank or leg, substantially as herein shown and described,
and for the purpose set forth.
2nd In compasses, dividers or callipers, the combination with the legs, of a worm
wheel held in the joint, a joint bolt, a nut screwed on the joint bolt and a worm
held in one of the shanks or legs, the said worm engaging with the worm wheel
substantially as herein shown and described and for the purpose set forth.
3rd In compasses, dividers or callipers, the combination with the legs, of a worm
wheel held in the joint, a joint bolt passed through the joint head and the worm
wheel, a nut screwed on the said bolt, a key screwed on the said bolt and a
worm held in one of the shanks or legs, the said worm engaging the worm wheel
substantially as herein shown and described and for the purpose set forth.
4th In compasses, dividers or callipers, the combination with the legs, of a worm
wheel held in the joint which wheel is flat on one side and has a recess in tho
other side, a joint bolt passing through the joint head and the worm wheel, a nut
screwed on the bolt and a worm held in one of the shanks or legs the said worin
engaging with the worm wheel, substantially as herein shown and described and
for the purpose set forth.
In witness whereof I the said Alexander Melvillo Clark, have hereunto set my
hand and seal this Twenty fourth day of December A.D. 1883.