represented by an inch. A fraction is often used, such as
opposite. Both parts carry the same number, but the part
1/500, meaning that one unit on the map is equal to 500
called for is distinguished by a dash and number. (LH
like units on the ground. A LARGE-SCALE MAP has
means left hand and RH means right hand.) Some
companies use odd numbers for right-hand parts and
a scale of 1" = 10"; a map with a scale of 1" = 1,000' is
even numbers for left-hand parts.
considered a SMALL-SCALE MAP.
Various types and shapes of scales are used in
preparing blueprints. Four common types are shown in
Zone numbers on blueprints serve the same purpose
as the numbers and letters printed on borders of maps to
ARCHITECTS' SCALES. Architects' scales
help you locate a particular point. To find a particular
(fig. 3-2, view A) are divided into proportional feet and
point, mentally draw horizontal and vertical lines from
inches and are generally used in scaling drawings for
these letters and numerals. The point where these lines
machine and structural work. The triangular architects'
intersect is the particular point sought.
scale usually contains 11 scales, each subdivided
differently. Six scales read from the left end while five
You will use practically the same system to help you
scales read from the right end. Figure 3-2, view A, shows
locate parts, sections, and views on large blueprinted
how the 3/16-inch subdivision of the architects' scale is
objects (for example, assembly drawings on ships'
further subdivided into 12 equal parts representing 1
steering gear). Parts numbered in the Title block can be
inch each, and the 3/32-inch subdivision is further
located on the drawing by looking up the numbers in
subdivided into 6 equal parts representing 2 inches each.
squares along the lower border. Zone numbers read from
right to left.
ENGINEERS' SCALES. Engineers' scales (fig.
3-2, view B) are divided into decimal graduations (10,
20, 30, 40, 50, and 60 divisions to the inch). These scales
are used for plotting and map drawing and in the graphic
The scale of the blueprint is indicated in one of the
solution of problems.
spaces within the Title block It indicates the size of the
METRIC SCALES. Metric scales (fig. 3-2, view
drawing as compared with the actual size of the part. The
C) are used with the drawings, maps, and so forth, made
scale may be shown as 1" = 2", 1" = 12", 1/2" = 1', and
in countries using the metric system. This system is also
so on. It also maybe indicated as full size, one-half size,
being used with increasing frequency in the United
one-fourth size, and so on.
States. The scale is divided into centimeters (cm) and
If a blueprint indicates that the scale is 1" = 2", each
millimeters (mm). In conversion, 2.54 cm are equal to
line on the print is shown one-half its actual length. If a
blueprint indicates that the scale is 3" = 1", each line on
GRAPHIC SCALES. Graphic scales (fig. 3-2,
the print is three times its actual length.
view D) are lines subdivided into distances
Very small parts are enlarged to show the views
corresponding to convenient units of length on the
clearly, and large objects are normally reduced in size to
ground or of the object represented by the blueprint.
tit on standard size drawing paper. In short, the scale is
They are placed in or near the Title block of the drawing
selected to fit the object being drawn and the space
and their relative lengths to the scales of the drawing are
available on a sheet of drawing paper.
not affected if the print is reduced or enlarged.
Remember: NEVER MEASURE A DRAWING.
Bill of Material Block
USE DIMENSIONS. Why? Because the print may
have been reduced in size from the original drawing, or
you might not take the scale of the drawing into
The Bill of Material block on a blueprint contains a
list of the parts and materials used on or required by the
consideration. Then too, paper stretches and shrinks as
humidity changes, thus introducing perhaps the greatest
print concerned. The block identifies parts and materials
source of error in actually taking a measurement by
by stock number or other appropriate number and lists
laying a rule on the print itself. Play it safe and READ
the quantity used or required.
the dimensions on the drawing; they always remain the
The Bill of Material block often contains a list of
standard parts, known as a parts list or schedule. Many
commonly used items, such as machine bolts, screws,
Graphical scales are often placed on maps and plot
turnbuckles, rivets, pipefittings, and valves, have been
plans. These scales indicate the number of feet or miles