IMPROVEMENTS IN APPARATUS FOR DRAWING GEOMETRIC CURVES
Year: 1857

page_text: LETTERS PATENT to Henry Johnson, of Crutched Friars, in the City of
London, for the Invention of "IMPROVEMENTS IN APPARATUS FOR DRAWING
GEOMETRIC CURVES."
Sealed the 14th May 1858, and dated the 17th December 1857.
PROVISIONAL SPECIFICATION left by the said Henry Johnson at the
Office of the Commissioners of Patents, with his Petition, on the
17th December 1857.
I, HENRY JOHNSON, of Crutched Friars, in the City of London, do hereby
declare the nature of the Invention for "IMPROVEMENTS IN APPARATUS FOR
DRAWING GEOMETRIC CURVES," to be as follows:-
The instrument consists of a bar or upright held in a vertical position
against a plane, and furnished with a metal point for a centre. To this bar or
upright is attached one end of a horizontal rod. The upright passes through
the horizontal rod or a small block fixed upon the end of it, so that the
horizontal rod may revolve round the upright as a centre. The outer end of
the horizontal rod is furnished with a drum or pulley, over which a chain or
band passes; one end of this chain or band is fixed to the centre upon a level
with the pulley, and the other end of the chain or band, after passing over the
pulley or drum, returns and is attached to a slide which carries a pencil or
marking instrument. The horizontal rod is caused to revolve round the

page_text: upright, and the chain or band is thus wound round the upright, each suc-
ceeding coil enclosing the preceding one, and the slide is drawn from the
centre towards the pulley or drum at the outer end of the horizontal rod, by
which a curve is traced by the pencil or marker progressively, increasing as it
is drawn from the centre. The centro is furnished with tubes, one or more of
which can be pushed down to increase the size of the centre when required.
Any modification of the size or shape of the centre, or of the size of the chain,
will affect the curve described by the pencil. The instrument may be varied
by using a boss revolving upon the upright with a slot in it, through which a
flat bar passes with teeth on one side gearing into the teeth of the pinion fixed
on the upright, so that as the boss revolves the bar which carries a pencil or
marker is moved by the pinion; several change pinions may thus be used at
different times to produce different curves; or, in place of pinions, a spiral
toothed rack, decreasing in diameter from the base upwards, may be used, the
toothed rack being kept up to its work by a spring.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Henry Johnson in the Great Seal Patent Office on the
17th June 1858.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRY
JOHNSON, of Crutched Friars, in the City of London, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Seventeenth day of December, in the year of our Lord
One thousand eight hundred and fifty-seven, in the twenty-first year of Her
reign, did, for Ierself, Her heirs and successors, give and grant unto me, the
said Henry Johnson, Her special licence that I, the said Henry Johnson, my
executors, administrators, and assigns, or such others as I, the said Henry
Johnson, my executors, administrators, and assigns, should at any time agree
with, and no others, from time to time and at all times thereafter during the
term therein expressed, should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN APPARATUS FOR
DRAWING GEOMETRIC CURVES," upon the condition (amongst others) that I, tho
said Henry Johnson, my executors or administrators, by an instrument in
writing, under my, or their, or one of their hands and seals, should par-
ticularly describe and ascertain the nature of the said Invention, and in what

page_text: manner the same was to be performed,. and cause the same to be filed in the
Great Seal Patent Office within six calendar months next and immediately
after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Henry Johnson, do hereby declare tho
nature of the said Invention, and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement
thereof, that is to say:-
This instrument consists of a bar or upright held in a vertical position
against a plane, and furnished with a metal point for a centre. To this bar
or upright is attached one end of a horizontal rod. The upright passes
through the horizontal rod or a small block fixed upon the end of it, so that
the horizontal rod may revolve round the upright as a centre. The outer end
of the horizontal rod is furnished with a drum or pulley, over which a chain or
band passes; one end of this chain or band is fixed to the centre upon a level
with the pulley, and the other end of the chain or band, after passing over the
pulley or drum, returns and is attached to a slide which carries a pencil or
marking instrument. The horizontal rod is caused to revolve round the
upright, and the chain or band is thus wound round the upright, each succeed-
ing coil enclosing the preceding one, and the slide is drawn from the centre
towards the pulley or drum at the outer end of the horizontal rod, by which a
curve is traced by the pencil or marker progressively, increasing as it is drawn
from the centre. The centre is furnished with tubes, one or more of which
can be pushed down to increase the size of the centre when required. Any
modification of the size or shape of the centre, or of the size of the chain, will
affect the curve described by the pencil.
And in order that my said Invention may be most fully understood and
readily carried into effect, I will proceed to describe the Drawings hereunto
annexed.
Figure 1 is a side view, and Figure 2 is a plan, of an instrument constructed
according to my Invention. a is the lower part of the upright, which is made
of wood and furnished with the metal point 6 to prevent its end from slipping
on the surface on which the instrument is employed; c is a metal axis driven
into the top of the piece a; d is a handle fixed by the set screw e to the end of
the axis c; the parts a, b, c, and d form the upright of the instrument; fis
a horizontal rod; it is for convenience divided into inches and parts of inches;
g is a block fixed to the end of this rod, and through this the axis c passes
mounted on the rod f. There is the slide h which carries the pencil i, by
which the curve is traced on the surface; j is a pulley at the end of the rod f;

page_text: and is a standard, having at its end a cross piece 1, which carries two small
wheels m, m, serving when the instrument is in use to keep the rod f accu-
rately parallel with the surface on which the curve is traced; n is a chain,
attached at one end to the axis c, which for this purpose has a conical bole
formed through it, and a corresponding cone is fixed to the end of the chain.
At the other end of the chain u a cord o is fixed, and this cord is taken round
the pulley j and attached to the slide h either directly or after it has first been
passed round the pulleys p and q one or more times, according to the nature of
the curve which it is desired to trace. The pulley p is mounted on a slide 1,
which is clamped by a binding screw to the rod f; and the pulley g is mounted
on another slide s, which is coupled by the screw and nut t to the slide h. In
order to trace the curve the upright of the instrument is placed vertically
against the surface to be marked, and the horizontal rod is carried round the
upright by hand, the chain is thus wound on the axis, and the slide, with its
pencil, is drawn progressively away from the centre. The chain is prevented
from surging on the axis by the supporting block and by the covering plate v,
which is slid down the axis into the position shown by dotted lines, and is
clamped in position by the binding screw w. Sometimes, in order to chango
the form of the axis, and consequently that of the curve traced by it, I employ
pieces y, y, which are fixed by screws to the block u, as is shewn; and in
order to change the diameter of the axis, but not its cylindrical form, I employ
the sliding tubes,,, which slip one over the other and are of different
lengths, so that one or more of them may be used as may be required.
The instrument may be varied by using a boss revolving upon the upright,
with a slot in it through which a flat bar passes, with teeth on one side,
gearing into the teeth of a pinion fixed on the upright, so that as the boss
revolves the bar which carries a pencil or marker is moved by the pinion;
several change pinions may thus bo used at different times to produco different
curvos, or in place of pinions, a spiral toothed rack or pinion decreasing in
diameter from the base upwards may be used, the toothed bar being kept up
to its work by a spring.
Figure 3 is a side view, and Figure 4 is a plan of an instrument constructed
in this manner. a is a metal axis, on which three pinions b, c, and d aro
fixed; this axis passes through the boss c, which is made in two parts, but these,
when the instrument is in action, are clamped together by the screws f,f;
tho axis a is furnished with a foot h, which is clamped to it by the set screw i,
its end enters one of three holes formed in the axis at different distances from
its end, corresponding with the depth of the pinions b, c, d; the foot his

page_text: further secured to the axis by the pin j, which is screwed into the axis, and
passes through a slot in the foot; k is a piece fixed to the boss e, and entering
a groove at the top of the foot h, so as to prevent the two parts from sepa-
rating. The flat bar e', having rack teeth on one side of it, slides through the
upper part of the boss e; it is kept in its position by the two loose pinions
m, m, and its teeth gear with one of the pinions b, c, and d. At the end of
the bar e¹, an arm n is keyed, and to this the pencil o is fixed; the method of
using the instrument for tracing curves is evident, the form of the curve pro-
duced will depend on which of the pinions b, c, and d is in gear with the rack.
In order to change the pinion, it is necessary to slack the screws f, f, and to
slide the upper part of the boss e as far from the axis as its slots will allow;
then the set screw i is also slacked, and the axis is drawn endwise in one or
other direction, until the pinion which it is desired to use is brought opposite
the rack teeth, and by sliding the upper parts of the bosse forward again,
theso teeth are caused to gear with the pinion, and the screws ff, are again
screwed tight.
Figure 5 is a side view, and Figure 6 is a plan, of another apparatus,
differing but slightly from that just described; there is a spiral pinion mounted
on the axis, and this, in place of simply passing through the boss e, has a wood
screw fixed on it, which screws into a female screw cut in the lower part of
the boss c, and the pitch of this screw is such, that as the arm is caused to
revolve as already described in tracing a curve it lifts the pinion with its axis
at the necessary speed to keep the rack in gear with the pinion; the rack is
kept constantly up to the pinion by a vulcanized india-rubber spring, as the
Drawing shews.
Figure 7 is a front view, and Figure 8 is a transverse section, of an instru-
ment in which the pinion on the axis, in place of giving motion direct to the
rack or bar, drives an intermediate axis, and it is a pinion on this axis which
actuates the rack or bar. The Drawings so fully shews the construction of
this instrument that no detailed description is required.
Figure 9 is a side view, and Figure 10 is a plan, of an instrument in which
the horizontal rod slides through a hole in the boss; but in place of a rack
and pinion, a cord winding on to the axis is employed, as in the instrument
first described. a the axis which passes through the boss b, and has a foot
c fixed to it by the set screw d; the horizontal rod e slides through a hole in
the boss, and carries a pencil e' at its end; f is a cord attached at one end to
the axis, and at the other, either directly to the end of the rod e, or it is first
passed round the pulley 7 fixed at the end of this rod, and then round a pulley

page_text: h fixed to the boss b; the cord passes one or more times round theso pulloys
according to the form of curve required. The standard i serves to keep the
rod parallel to the surface to be marked; it will be seen that the axis
a may readily be changed for an axis, having a different form of spiral formed
on it when desired.
In witness whereof, I, the said Henry Johnson, have hereunto set my
hand and seal, this Sixteenth day of June, in the year of our Lord
One thousand eight hundred and fifty-eight.
Witness,
GEO. PITT.
HY JOHNSON. (L.S.)