Zone Numbers

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

Zone Numbers

preparing blueprints. Four common types are shown in

figure 3-2.

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,

Scale

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

1 inch

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

same.

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

3-4