IMPROVEMENTS IN APPARATUS FOR DRAWING ELLIPSES
Year: 1880

page_text: PROVISIONAL SPECIFICATION left by Frank Wirth at the Office of the
A communication from
Commissioners of Patents on the 14th May 1880.
Gustav Nolten, of Dortmund, in the Empire of Germany.
FRANK WIRTH, of the Firm of Wirth and Company, Patent Solicitors, at
Frankfort on the Main, in the Empire of Germany. "IMPROVEMENTS IN APPARATUS
FOR DRAWING ELLIPSES." [A communication from Gustav Nolten, of Dortmund,
in the Empire of Germany.]
The construction of one part of the apparatus, which forms the subject of this
Invention, is based on the known mathematical problem, that if two concentric
circles are drawn respectively with the semi major and minor axes of an ellipse as
radii, and any radial line intersecting both circles be drawn, then the point of
intersection of two lines drawn respectively through the intersection of the radial
line with the larger circlo, and parallel with the minor axis, and through the
intersection of the radial line with the smaller circle and parallel with the major
axis, will be a point in the elliptic curve.
In constructing an apparatus for drawing ellipses according to this method, two
rectangular frames are made to slide the one upon the other in directions at right
angles to each other between fixed guides on a board or base. Each frame has, at
about the middle of its length, two transverse parallel bars at a small distance
apart, so that the bars of the one frame cross those of the other frame, thus forming
at their intersection a small rectangular space into which a rectangular bar
carrying a pen, pencil, or style is fitted. A radius bar, turning with its one end in
a centre in the base, has, at distances from such centre corresponding to the semi
major and minor axes of the ellipse desired to be drawn, studs that fit respectively
into the spaces between each pair of cross bars. Thus, on turning the radius bar on
its centre, it will by means of its studs cause the two frames to travel at right
angles to each other, and the pen, pencil, or style, carried thereby will thus be made
to draw the corresponding elliptic curve. In practice it is necessary to actuate each
frame by a separate radius bar, representing respectively the semi major and minor
axes, both of which are made to move simultaneously at the same speed with their
studs in two other sets of cross bars carried by the frames, the simultaneous
movement of the radius bars being effected by means of two toothed wheels of
equal diameter on one which each bar is mounted, in gear with both of which
wheels is another wheel rotated by a pinion. The radius bars are grooved, and

page_text: contain slides carrying the before mentioned studs representing the extremity of
the radius, so that these studs can be adjusted at a greater or less distance from the
centre to suit different proportions of the major and minor axes of the ellipse to be
drawn. For accuracy of adjustment each radius bar has a scale marked on its edge
to which the slide is set. The one radius bar is mounted directly on its toothed
wheel, while the other is mounted on a disc with graduated edge that can be
adjusted relatively to an index on another disc carried by the axis of its toothed
wheel at some height above the latter, in order to suit the different levels of the
two sliding frames, which are made of some height so as to afford a steady guide to
the pen or pencil, that is to say, there is to one an upper and a lower sliding frame
with its cross bars, while the other frame sliding within the double one has upper
and lower cross bars to it.
The above named adjustment of the one radius bar relatively to its toothed wheel
and consequently to the other radius bar enables ellipses to be drawn whose axes
are oblique to the direction of the motion of the sliding frames. In order to enable
definite portions of elliptic curves to be drawn at definite distances apart, each of
the toothed wheels carrying the radius bars has pointers moving over graduated
circles so as to enable the wheels with their arms to be turned, and consequently
the pen or pencil carried by the frames to be moved through definite distances.
The pen, pencil, style or graver, may be of any suitable construction. By
preference, it consists of a hollow rectangular bar, fitting accurately the before
mentioned rectangular space between the cross bars of the frames, through which
bar slides a rod carrying the marking instrument. The upper end of the hollow bar
has a collar with which it rests on the cross bars and which has projections on its
upper face; the rod carrying the pen or pencil has also an adjustable collar so
arranged that by lifting the rod so that its collar rests on the projections of the bar
collar, the marking instrument is held in a raised position away from the surface on
which the ellipse is being drawn, while by turning the rod into another position
the instrument descends on to and marks such surface. The accurate adjustment
of the before described sliding studs in their radius bars may be effected either by
moving them by means of micrometer screws of well known arrangement, or by
providing in the groove of the radius bar an adjustable stop, against which is held
a wedge shaped guage adjusted to a scale on a separate bar, the sliding stud being
moved till it bears against the said guage.
Another part of the Invention relates to an adjusting apparatus, by means of
which the entire instrument above described is rendered adjustable in any required
direction over the surface on which elliptic curves require to be drawn. This apparatus
is constructed as follows :-A rectangular frame, which rests upon the said surface,
has a groove along one of its sides in which slides a bar of a second frame, the bar
and frame being moved by a rack and pinion with crank handle. The sliding
frame has also a groove at right angles to that of the main frame, in which slides a
bar to which the before described instrument is attached, and this bar, together with
the instrument, is moved along the groove by another rack and pinion. In each of
the said grooves is an adjustable stop for limiting the motion of the sliding frames
to the exact extent required, and micrometer screws are provided for accurate
movement through minute distances. To the base of the drawing instrument is
attached a straight edge, having a nick by which the instrument can be accurately
set to a copy fixed above the frame, of which copy the instrument is required to
reproduce the design.