[Illustration: Fig. 236.]
“Inking In” Drawings.
When a drawing is completely finished in penciling, it should next be
“inked in” for preservation.
Care should be used that the pen may be perfectly clean; the pen should
be held nearly vertical, leaning just enough to prevent it from catching
on the paper; the pen should be held between the thumb and first and
second fingers, the knuckles being bent, so that it may be at right
angles with the length of the hand.
The ink should be rubbed up fresh whenever it is about to be used, for
it is better to waste a little time in preparing ink slowly than to be
at a continual trouble with pens, which will occur if the ink is ground
too rapidly or on a rough surface.
To test ink, a few lines can be drawn on the margin of a sheet, noting
the shade, how the ink flows from the pen, and whether the lines are
sharp. After the lines have dried, cross them with a wet brush; if they
wash readily, the ink is too soft; if they resist the water for a time
and then wash tardily, the ink is good.
Care must be exercised not to overload the pen with ink, and, like the
pencil, the pen should always be moved from left to right and from the
bottom to the top of the board. When inking, both “nibs” of the pen
point must rest evenly on the paper and the pen be pressed only lightly
against the T-square. Never ink any portion of a drawing until the
penciling is complete.
In inking long, fine lines it is well to go over each line twice,
without moving the T-square, trying not to widen the line on the second
passage; also see that the pen contains ink enough to finish a line, as
it is difficult to continue with the same width of line after
re-filling.
To produce finished drawings, it is necessary that no portion should be
erased, otherwise the color applied will be unequal in tone; thus, when
highly finished mechanical drawings are required, it is usual to draw an
original and to copy it. Where sufficient time cannot be given to draw
and copy, a very good way is to take the surface off the paper with fine
sand-paper before commencing the drawing; if this be done, the color
will flow equally over any erasure it may be necessary to make
afterwards.
The rules of procedure in drawing the lines in “inking” are, 1, ink in
the small circles and curves; 2, ink in the larger circles and curves;
3, then all the horizontal lines, beginning at the top of the drawing
and working downward; 4, next ink in all the vertical lines, commencing
at the left and moving back to the right; 5, draw in the oblique lines;
6, all the center lines and dimension and reference lines. The figuring
and lettering should be always done with India ink, thoroughly black;
the last lines to be drawn are the section lines. The reason why
irregular curves and arcs of circles are inked in first is, that it is
easier to draw a straight line up to a curve than to take a curve up to
a straight line.
In practice, the flat side of the drawing-pen is laid against the
tee-square or ruler; the taper of the blade of the pen is sufficient to
throw the point enough away from the edge to prevent blotting; the pen
is drawn from left to right and from the bottom to the top of the board.
This is shown in fig. 237, intended to represent “short work” with the
drawing-pen. The wrist is shown resting upon the blade of the square.
[Illustration: Fig. 237.]
[Illustration: Fig. 238.]
In a similar figure, 238, the position of the hand holding the pen
indicates the best relative posture for inking long lines. In one of
these illustrations the work is executed principally by the wrist--in
the other by the arms and fingers working together.
The pen should be held with even pressure against the straight-edge or
curve. If the pressure varies, the blades will spring and the width of
the line will change. The blades should be of such length that both will
bear equally upon the paper when the pen is inclined slightly, so as to
bring the inner blade near the straight-edge; the angle of the pen
should not be changed while drawing any line.
When the inking is finished, the whole drawing may be cleaned by rubbing
it with bread which is not greasy or so fresh as to stick to the paper.
If the paper is much soiled it may be necessary to use an eraser. A soft
pencil eraser should be used and great care taken that the ink lines are
not lightened and broken by it.
To avoid the necessity of using an eraser upon a finished drawing,
instruments and paper must be kept free from dust and dirt. The
triangles and T-square should be cleaned often, by rubbing them
vigorously upon rough, clean paper.
Pounce is a powder used to prevent blotting in rewriting over erasures;
it is held in a bag or small box with a perforated lid for convenience
in sprinkling on paper; when used it should be distributed evenly with a
piece of chamois, and the surplus or loose particles removed before
applying the ink.
A drawing is made to be read, and the skill in inking, as in “free-hand”
and in penciling, does not consist so much in the fineness of the lines
as in their clearness.
Lettering Drawings.
Lettering is an important part of making drawings, the object aimed at
being to identify any portion by reference letter or letters; thus in
fig. 239 the line _A C_ describes the line extending from
[Illustration: Fig. 239.]
Any information which cannot be expressed in the drawing is always
expressed by lettering, and it is desirable to confine the lettering of
drawings to one or two standard alphabets that are plain and distinct,
and the principles of which are easily acquired. These conditions are
fulfilled in the Gothic fonts shown on page 173.
Both letters and figures must be carefully made and of uniform
proportion; it is well to “lay out” these by regular measurement before
permanently inking them. Letters should not be less than one-eighth of
an inch in height and penciled carefully before inking.
On page 173 are printed two forms of numerals and letters of the
alphabet; it is recommended that these be used both for practice in
free-hand and for regular office work.
For easy reference, letters should not be crowded nor allowed to
interfere with one another; they should be drawn neatly, avoiding all
lines of the drawing; plain letters are always used on mechanical
drawings, whether for title, scale, reference, etc.
Arrow-heads, figures and letters should be in black, and made with a
writing pen. A pen with a ball point is preferable, giving an equal
thickness of line, no matter in which direction the stroke is made.
[Illustration: Fig. 240.]
Neat, well-lettered drawings go far towards establishing a high standing
for the aspiring draughtsman. All lettering should be done free-hand,
first with the pencil, sharpened to a fine round point, and afterwards
written in ink. For this purpose common writing pens are best to be
used; fig. 240 represents the several numbers of the approved Gillott’s
pens adapted to this purpose.
In lettering, it is well, for a guide for size and location, to draw,
with a round-pointed pencil, two horizontal lines just the height the
letters are to be; the letters are also best made with careful use of
the instruments, rather than free-hand.
In order to letter systematically, it is a good plan to start with the
middle letter of the inscription and work in both directions; making too
prominent letters should be avoided, plain and distinct letters being
most desirable.
Finally, with an ordinary writing pen, trace over the penciling in ink;
the pencil guide lines being erased after the letters are inked in
completes the operation.
[Illustration]
An important matter in connection with lettering a drawing is the
location of the letters; these should be so placed as not to interfere
with the lines of the drawing and should clearly point out the part
intended to be described. When single letters are used, they should be
inked in before the shade or section lines are drawn.
Fig. 241 is an example introduced to show the method of lettering a
descriptive mechanical drawing.
The figure shows a “blow-off valve” of approved design drawn in section;
the letters designate the several parts; the reading to accompany the
lettering is as follows:
=A=--Inlet communicating with annular passage (_C_) to admit steam,
which blows off scale and sediment from seat (_E_) before disc (_L_)
comes in contact with same.
=B=--Plug to permit passage of rod to clean out blow-off pipe.
=C=--Annular steam passage around casing (_D_) and communicating with
inlet (_A_).
=D=--Removable bronze casing, in which plug (_L_) fits snugly.
=E=--Removable bronze seat ring, which also holds casing (_D_) in
place.
=J=--Slot in casing (_D_) arranged to discharge sheet of steam from
_C_, which, blowing across seat (_E_), cleans off scale and sediment
before contact with disc (_L_).
=K=--Non-rotating washer to prevent loosening of locknut (_H_) when
opening valve.
=L=--Reversible disc, having two Babbitt-metal seating faces (_F_)
(_F_).
[Illustration: Fig. 241.]
Dimensioning Drawings.
To “dimension” working drawings is to place measurements upon the parts
represented, to enable the workman to proceed without measuring the
drawing itself.
These dimensions should be placed so as not to interfere with nor crowd
the lines of the drawing, nor yet interfere with one another.
Arrow-heads are used at the extreme points of measurement, the figures
are generally inserted midway between the arrows; a dot and dash line
reaches from the figure to the arrow-heads, as shown below.
[Illustration]
When the dimension is short these lines are omitted and the dimension is
placed outside the drawing, thus
[Illustration]
and connected by a curved line; at other times it is found needful to
place arrow-heads outside the drawing and the measurement inside.
[Illustration]
When the dimension is long and narrow it is usual to carry the
dimensions under the drawing by dotted and dash lines, as shown below.
[Illustration]
Arrow-heads and figures should be drawn free-hand with a common writing
pen.
Usually dimensions are given in inches, up to 24 inches, as it is found
less confusing; for instance, if written 1′ 1″ it may be mistaken for
11″; if written 13″ no mistake could be made.
Again, 1′ 0″ may be mistaken for 10″; if written 12″ it would not; in
addition to being more distinct, it occupies less space on the drawing.
In large measurements there is more room for the figures, and,
therefore, they can be spaced further apart--in feet and inches.
All figures should be made of a fairly large size. Vertical dimensions
should read from the right hand, thus, as shown:
[Illustration]
Measurements of importance, such as the diameter of a circle, the pitch
or distance apart of rivets and bolts, etc., should be marked in figures
on the drawing. When rough or unfinished work is mixed with machined or
finished portions, it is usual to mark F, or “fin.,” after the latter
dimension.
In practice, at times, instead of dimensions reference letters are used,
thus:
[Illustration:
D = diam. of shaft, 2¹⁄₂ inches.
L = length of bearing, 3³⁄₄ inches.
T = thickness of collar, ⁷⁄₈ inch.
d = diam. of collar, 3¹⁄₂ inches.]
Generally it is preferable to give the diameters of turned and bored
work on a section, instead of an end drawn separately; confusion is
sometimes caused by a number of radial dimensions.
Fig. 242 and fig. 243 are introduced to show the principal measurements
required in practical work, and the usual way in which such dimensions
are marked when ordering parts of machinery.
Fig. 242 is a pedestal, or metal frame; three views are shown, the
center figure being an elevation, the lower figure is the plan of the
base, the upper figure is a view of the top, on which is bolted the
bearing block, it being on the outside of the center figure. The
essential measurements are marked by letters. _H_ is the vertical height
from base to the seat of bearing block: _L_ being the length, and _W_
the width of the base; _P_ is the length between checks, and _B_ the
width of seat for bearing block; _C_ is the distance from center to
center of the holding down bolt holes, and _T_ is the depth of the holes
in the base; _K_ is the distance from center to center of the bolt holes
in the top for bearing block.
Fig. 243 is a hanger, or metal bracket, and shows the center figure or
elevation, the plan of the top and the plan of the seat for bearing
block, which is bolted on the interior of the center figure. _H_ is the
vertical distance from the top to the seat for bearing block; the other
measurements required are marked by letters similar to figure 242.
Now, one of the important matters in connection with dimensioning a
drawing is the location of the figures. One rule, whose utility cannot
be gainsaid, is that they should be so located that they can be altered
or erased without damage to the lines of the drawing, as changes may be
necessitated either by original errors in writing down the figures or by
changes in the design being found desirable during the construction of
the machine.
[Illustration: Fig. 243.--Fig. 244.]
Shading Drawings.
To produce an effect, drawings are shaded; that is, shadow lines about
twice the width of the regular line are drawn according to a recognized
rule, which always represents the same peculiarity of form in the same
way.
In working drawings light lines only are permitted; shade lines are
wider than the working lines, and in reading scale measurements the
extra thickness of line would make a difference.
Instead of representing the shadow as it is really cast by the object,
the edges which cast the shadow are determined, and all the views are
treated as if the light came from behind and from the left, downwards,
at an angle of 45° to the horizontal line, as shown by the arrows in
figs. 245 to 248.
[Illustration: Fig. 245.--Fig. 246.--Fig. 247.--Fig. 248.]
The lower and right-hand outlines of projecting parts will cast shadows,
and the student should make them of extra width.
Fig. 249: In shading curves, divide the center line as before (see page
146) and describe circles from center, _D_; these lines are not to be
shaded in penciling, but when inking. The figures represent two rings,
_A_ and _C_, and spaces, _B_ and _D_. The outside of a surface is shaded
according to circle 1, and the inside surface according to circle 2.
This will give the desired shading, but it makes a drawing incorrect,
and therefore shading is not used in working drawings.
This shading is accomplished by inking the circle first with regular
width of line; then with the same radius remove the point of compasses
from the _true center_, placing it outside, according to the desired
position of the shaded line, and describe an arc of a circle.
In fig. 250 divide center line as before; with the 45° triangle or set
square, draw through the center the diagonals shown by dotted lines; and
through the points _A_, _B_, _C_, etc., draw the perpendiculars, cutting
the diagonals; from the points of intersection draw the horizontal
lines, completing the squares.
[Illustration: Fig. 249.]
[Illustration: Fig. 250.]
Now, take a radius of half an inch, and in the corner of each square
draw with the bow-pencil a circular arc meeting the pencil lines
exactly; with the bow-pen _ink in the arcs_ first, then ink carefully
the lines joining with the arcs; all lines must be of the same width;
put in the shade on arcs and lines as in fig. 249; and, finally, erase
the pencil lines at corners, etc.
Section-Lining.
Cross-hatching has been defined in the “preliminary definitions” to
drawing; this term represents the practice of drawing diagonal lines
representing the interior of an object, shown as a piece cut in half or
when a piece is broken away. This is done to make more of the parts
show, or to exhibit more clearly the nature of the materials; hence
section lining and cross-hatching tell the same thing, _i. e._, the
drawing of diagonal lines, usually at an angle of 45°, to show that the
object is broken away and the interior designed to be represented.
[Illustration: Cast iron.