DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.20658#0026
OF DRAWING.
crum ; the tracing point c is to be moved over all the lines of the original drawing (the drawing
being kept steady by a weight), and the pencil at the box b will describe lines on a paper, placed
under it, exactly similar and equal to those of the original.
To copy a drawing when it is it to be onhj half the size of the original. Set the boxes b and i>
to the division marked §; the fulcrum must now be placed at b, the crayon or pencil at d, and
the tracer at c, as before. The instrument in tins case is used as in the former, except that it
rests on the fulcrum at b, where the pencil was placed in the former ease.
If it be required to make a drawing less than half the size of the original, as for instance, one-
third, one-fourth, or one-fifth, Sec. the boxes b find r> are to be set to the divisions marked j,
or |, on the longer scales; and the crayon placed at n, and the tracer at c, as before. And it must
be observed, that when a copy is to be less than half the original, or when it is required greater
than the original, the longer scales are always to be used.
To make a drawing greater than one half ' the original. If it be required to make a drawing of
the size of two-thirds, three-fourths, or four-fifths, of the original, the boxes b and u are to be set
to the fractions j, f, or ^ on the shorter scales. In this case the fulcrum is placed at d, and the
crayon at b, as in the first case, when the drawing was to be the same size with the original.
When it is required to make a drazoing larger than the original. Suppose it were required to
make a drawing one-sixth larger than the original; the boxes b and r> are to be set to the division
marked ^ on the longer scales, and the fulcrum is to be placed at d, the crayon at c, and the
tracer at b.
When the drazoing is required of a size different from any of the fractional parts on the instru-
ment. There are twro scales of numbers laid down upon the instrument for this purpose, containing
100 unequal parts : one scale is numbered from 10 to 80, the other from 50 to 100. And if it be
required to make a drawing less than half the size of the original, the numbers under 50 on the
scale are to be used ; but if the drawing is to be larger than half the original, the numbers from.
50 to 100 are to be taken. In both cases the boxes b and d are to be set to the numbers corre-
sponding to the sizes of the original and copy respectively ; and the crayon is to be placed at d,
the fulcrum at b, and the tracer at c.
To move the pentograph and shift the paper. When a drawing from a large original is required,,
it becomes often necessary to move it, in order to copy the different parts of it : in which case
there should be three points made on the original, or a small triangle drawn thereon with the
tracer, and a similar one on the copy with the pencil or crayon, and by means of the instrument.
Then, when the instrument and drawings are shifted, they must be so placed, that when the tracer
is applied to the three points, or three angles, of the triangle on the original, the crayon or pencil
mav exactly coincide with the other three points or angles on the copy. This precaution must
be taken every time the drawings are removed.
The sectoral compasses. Combine together, 1. the sector already described ; '2. the beam com-
passes for drawing circles or arches to a large radius; 3. elliptic compasses for drawing ellipses or
ovals ; and, 4. the calliper compasses. In this instrument, a is a square for drawing ellipses,
or ovals; b c the points which work therein: and d e are the calliper points.
The elliptical compasses are also made by themselves : their use will appear upon inspection ; for
by means of the sliders running in the grooves, the pencil or crayon fixed at the end of the beam will
describe half an ellipse : then, by changing the situation of the compasses, and placing them in the
opposite
crum ; the tracing point c is to be moved over all the lines of the original drawing (the drawing
being kept steady by a weight), and the pencil at the box b will describe lines on a paper, placed
under it, exactly similar and equal to those of the original.
To copy a drawing when it is it to be onhj half the size of the original. Set the boxes b and i>
to the division marked §; the fulcrum must now be placed at b, the crayon or pencil at d, and
the tracer at c, as before. The instrument in tins case is used as in the former, except that it
rests on the fulcrum at b, where the pencil was placed in the former ease.
If it be required to make a drawing less than half the size of the original, as for instance, one-
third, one-fourth, or one-fifth, Sec. the boxes b find r> are to be set to the divisions marked j,
or |, on the longer scales; and the crayon placed at n, and the tracer at c, as before. And it must
be observed, that when a copy is to be less than half the original, or when it is required greater
than the original, the longer scales are always to be used.
To make a drawing greater than one half ' the original. If it be required to make a drawing of
the size of two-thirds, three-fourths, or four-fifths, of the original, the boxes b and u are to be set
to the fractions j, f, or ^ on the shorter scales. In this case the fulcrum is placed at d, and the
crayon at b, as in the first case, when the drawing was to be the same size with the original.
When it is required to make a drazoing larger than the original. Suppose it were required to
make a drawing one-sixth larger than the original; the boxes b and r> are to be set to the division
marked ^ on the longer scales, and the fulcrum is to be placed at d, the crayon at c, and the
tracer at b.
When the drazoing is required of a size different from any of the fractional parts on the instru-
ment. There are twro scales of numbers laid down upon the instrument for this purpose, containing
100 unequal parts : one scale is numbered from 10 to 80, the other from 50 to 100. And if it be
required to make a drawing less than half the size of the original, the numbers under 50 on the
scale are to be used ; but if the drawing is to be larger than half the original, the numbers from.
50 to 100 are to be taken. In both cases the boxes b and d are to be set to the numbers corre-
sponding to the sizes of the original and copy respectively ; and the crayon is to be placed at d,
the fulcrum at b, and the tracer at c.
To move the pentograph and shift the paper. When a drawing from a large original is required,,
it becomes often necessary to move it, in order to copy the different parts of it : in which case
there should be three points made on the original, or a small triangle drawn thereon with the
tracer, and a similar one on the copy with the pencil or crayon, and by means of the instrument.
Then, when the instrument and drawings are shifted, they must be so placed, that when the tracer
is applied to the three points, or three angles, of the triangle on the original, the crayon or pencil
mav exactly coincide with the other three points or angles on the copy. This precaution must
be taken every time the drawings are removed.
The sectoral compasses. Combine together, 1. the sector already described ; '2. the beam com-
passes for drawing circles or arches to a large radius; 3. elliptic compasses for drawing ellipses or
ovals ; and, 4. the calliper compasses. In this instrument, a is a square for drawing ellipses,
or ovals; b c the points which work therein: and d e are the calliper points.
The elliptical compasses are also made by themselves : their use will appear upon inspection ; for
by means of the sliders running in the grooves, the pencil or crayon fixed at the end of the beam will
describe half an ellipse : then, by changing the situation of the compasses, and placing them in the
opposite