The first thing to be considered in selecting drawing paper is the kind
most suitable for the proposed plan. Paper may be purchased in sheets 22
× 30 inches, that make four exercise sheets 11 × 15 inches; this may be
of several grades and tints.
The qualities that constitute good paper are strength, uniformity of
thickness and surface, neither repelling nor absorbing liquids,
admitting of considerable erasing without destroying the surface, not
becoming brittle nor discolored by reasonable exposure or age, and not
buckling when stretched, or when ink or color is applied.
The sizes and names of paper made in sheets is as follows:
Cap 13×17 ins.
Demy 15×20 „
Medium 17×22 „
Royal 19×24 „
Super Royal 19×27 „
Imperial 22×30 „
Atlas 26×34 „
Double Elephant 27×40 „
Antiquarian 30×53 „
For large drawings paper is made in rolls. “Detail paper” is especially
made for marking out new designs; it is made in rolls 36, 42 and 54
inches wide; it has excellent erasing qualities and takes ink and color
with facility.
When working by artificial light it is desirable that the paper be of a
light-brown color, which is less trying to the eyes than a pure white.
If it is a shop drawing or sketch not to be preserved, use detail paper,
which is the most economical and will stand a great deal of handling
without becoming soiled. If it is a detailed plan, finished drawing or a
picture, use the best white drawing paper to be obtained, so that your
drawings can be preserved indefinitely without danger of fading, which
is due either to the paper being poorly made and discoloring with age,
or being of poor fiber and absorbing the ink or color, and the drawing
consequently losing its brightness.
After deciding on the size of paper most suitable for the work, then
carefully select the paper embracing the most qualities of value for the
proposed drawing.
[Illustration: Fig. 208.]
[Illustration: MECHANICAL DRAWING]
[Illustration: Fig. 209.]
Mechanical Drawing.
In distinction to “free-hand,” mechanical drawing is executed almost
entirely by the use of the instruments previously described; hence its
other term, instrumental drawing. To define it particularly it may be
said that,--
Mechanical drawing is the correct reproduction of any figure or part of
a machine, whether of full size or reduced in the proportion of one part
to another; it also comprises the art of delineating the interior parts
which are hidden from view in solid bodies.
A mechanical drawing is the vehicle for conveying the ideas of the
designer to those who are to embody them in wood and metal, and the
considerations which should govern its production are those which affect
its clearness and legibility or those which facilitate reference to it.
Drawings consist of plans, elevations and sections; plans being views on
the top of the object in a horizontal plane; elevations, views on the
sides of the object in vertical planes; and sections, views taken on
bisecting planes, at any angle through an object.
Drawings in true elevation or in section are based upon flat planes, and
given dimensions parallel to the planes in which the views are taken.
Two elevations taken at right angles to each other fix all points, and
give all dimensions of parts that have their axis parallel to the planes
on which the views are taken; but when a machine is complex, or when
several parts lie in the same plane, three and sometimes four views are
required to display all the parts in a comprehensive manner.
A man must have either a natural talent for hand-drawing or years of
experience, before he can produce a sketch and “dimension” it, fit to
work from; hence the elementary character of the examples given for
practice. A “pretty” drawing is not expected from a beginner; it should
always be borne in mind, that correctness of dimensions and general
clearness, rather than elaborate finish, are what will save the battle
in the days of competition.
Mechanical drawings should be made with reference to all the processes
that are required in the construction of the work, and the drawings
should be responsible, not only for dimensions, but for adaptation to
fitting, forging, pattern-making, moulding, and so on.
Every part laid down should have something to govern it that may be
termed a “base”--some position which, if understood, will suggest size,
shape and relation to other parts. Searching after a base for each and
every part and detail, the draughtsman should proceed upon a regular
system, continually maintaining a test of what is done.
A mechanical drawing consists chiefly of three views:
1. The plan or top view.
2. The side elevation.
3. The end elevation.
In addition to the above, drawings are used to show interior portions of
the figure; these are termed “sections,” and they may be taken where any
plane crosses another.
NOTE.--The word _elevation_, as applied to mechanical drawings, means
simply a view; hence a side elevation is a side view, or an end
elevation is an end view.
The word _plan_ is employed in place of the word top; hence a plan
view is a top view or a view looking down upon the top of the piece.
A _general_ view means a view showing the machine put together or
assembled, while a detail drawing is one containing a detail, as a
part of the machine or a single piece disconnected from the other
parts of the whole machine.
Penciling.
[Illustration: Fig. 211.]
It is very nearly true, as has been said, that every mechanical
drawing is, in the first instance, penciled; if this is so, then more
work is done with the pencil than with the pen; therefore the first
attention of the student of mechanical drawing should be directed to
the following instructions for penciling a drawing.
With all necessary materials in hand, and in good order for the
beginning of a drawing, the first thing to do is to pin the paper on
the board quite square.
To do this effectively, lay the paper flat and put on the T-square
with its head at the left side of the board; slide the square up
nearly to the top, and arrange the paper level with the blade; with
the right hand hold the paper still and move the square down a little;
now, pin the top of the paper with thumb-tacks.
Next, pressing the square lightly to the paper, slide it down to the
bottom and pin that part of the paper to the board. The paper must not
project outside or over the edges of the board, and the pins or
tack-heads should be forced down flush with the paper, so as not to
interfere with the free movement of the tee-square up and down the board
as occasion may require.
The accuracy of the work depending upon their condition, it is first
needful to see that the pencil and pencil compasses are properly
sharpened. Reference is made to valuable directions contained on pages
beginning with 55, under the heading of “Free-hand Drawing,” to which
may be added that--
All lines should be drawn with the pencil slightly inclined in the
direction in which it is moved.
Any and all lines not needed in the finished drawing should be erased at
one time after the final lines have been determined, for the surface of
the paper is soiled very quickly when worked upon after erasures have
been made.
The working lines and other lines that are to be removed should be
erased when the drawing is ready to finish and before its outlines have
been strengthened, in order that the final lines may be left in perfect
condition.
To show where the lines meet or terminate it is needful that all pencil
lines pass the actual ending place, making a distinct intersection. This
does not apply to “inking in” the lines, but rather to prevent the
over-drawing of the ink lines, because the edge of the rule and the pen
itself obstruct or partly cover the view of the line, it is very liable
to pass over or beyond the required point in inking the lines, which
must not occur.
In the preliminary operation of producing a regular mechanical or
instrumental drawing, it is necessary to make a “sketch,” in pencil, of
the object to be represented. The AMERICAN MACHINIST has given in a few
words the order to be followed, in effecting the best results; we quote,
as follows:
“In making a free-hand sketch of an object from the model it is well to
observe the following order: Look the model over carefully and determine
the number of views necessary to illustrate it fully, drawing the same,
free-hand, in their proper relation to each other, on sketching paper.
Look the sketch over carefully to see that nothing has been omitted, and
put on dimension lines, after which scale the model carefully and put on
dimensions. Do not put in the dimensions at the same time the dimension
lines are drawn; have all the dimension lines in place before attempting
to insert dimensions.
“Follow the same order in making the drawing with instruments as was
used in making the sketch; that is, draw the views in their proper
relation to each other, put in dimension lines, then dimensions, and
lastly notes and title. If section drawing is made, do not draw section
lines in pencil.”