IMPROVEMENTS IN THE MANUFACTURE AND CONSTRUCTION OF MATHEMATICAL DRAWING INSTRUMENTS
Year: 1873

page_text: PROVISIONAL SPECIFICATION left by John Norris at the Office of
the Commissioners of Patents, with his Petition, on the 11th
February 1873.
I, JOHN NORRIS, of Birmingham, in the County of Warwick, Manu-
facturer, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE MANUFACTURE AND CONSTRUCTION OF MATHEMATICAL
DRAWING INSTRUMENTS," to be as follows:-
My Invention relates to the mathematical drawing instruments called
compasses, bow pens, bow pencils, and straight pens, and to the loose
parts which are capable of being connected with and disconnected from
compasses, such as the loose leg pencil and pen and lengthening bar,
the said loose parts being commonly called "half sets."
My Invention consists principally in manufacturing the said instru-
ments by the process or combination of processes herein-after described,

page_text: whereby facility of production, economy of manufacture, and increased
strength in the instruments are secured.
In manufacturing the said instruments according to my Invention I
make them of the kind of cast iron called malleable or annealed cast iron,
that is to say, cast iron which by being heated or annealed in contact
with haematite or oxide of iron becomes malleable, and I form the parts
of the said instruments of the said malleable or annealed cast iron by
casting them in sand or other moulds, each leg or part of the instrument
being made in one piece. For example, in manufacturing a pair of
compasses according to my Invention I make each limb or leg of the 1
compass of a single piece of malleable or annealed cast iron, and joint
the said limbs or legs. together in the ordinary way. The point ends of
the said legs are casehardened or converted into steel by the ordinary
casehardening processes; or steel points may be put in the moulds and
fixed to the legs by the casting process. When the compass is to be
provided with a loose leg one of its limbs or legs is made shorter than
the other and is furnished with a socket to receive the stem of the said
loose leg, or the loose pen, or loose pencil commonly used with such
compasses.
Instead of malleable cast iron, cast steel may be used with the same
or nearly the same effect. When I use malleable cast iron I anneal the
articles after casting by heating them in contact with oxide of iron.
But when cast steel is employed the ordinary process of annealing by
heating and slow cooling is sufficient. I manufacture bow pens, bow
pencils, and straight pens, and the loose legs, pens, and pencils of 1
compasses in the manner described with respect to a pair of compasses.
The parts of the instruments so made are polished and their surface
coated with an electro-deposit of brass or German silver to prevent
oxidation.
Instead of securing the loose leg, loose pencil, and loose pen to the
short leg of the compass by a detachable screw, as usual, I dispense with
the said detachable screw and connect the said loose parts to the short leg
of the compass by screwing, that is to say, I make on the end of the
loose leg or other loose part a convex screw which takes into a hollow
or concave screw in the socket of the short leg of the compass.
By this
arrangement the attachment of the loose leg or other parts to and their
detachment from the compass is effected by the screwing of the loose

page_text: part itself into or out of the short leg instead of by the use of a separate
screw which is readily detached from the compass and lost.
The method described of connecting the loose leg, pen, and pencil to
the short leg of the compass is applicable to all the loose parts of a
compass and to drawing instruments made in the ordinary way.