Blue Print Reading
Level 1
Overview
Prints: the Language of Industry
You have heard the saying, “A picture is worth a thousand words”. This is certainly true when
referring to an airplane part.
It would be next to impossible for an engineer or designer to describe in words the shape,
size, and relationship of the various parts of an airplane in enough detail for skilled workers
to produce the part. Drawings are the universal language used by engineers, designers, and
skilled workers to share quickly and accurately the necessary information to create parts, put
together and service airplanes and other complex assemblies.
The original drawing that is created in an engineering department is kept in a vault, and
paper and Mylar copies are made to be used on the shop floor. Drawings used to be done by
hand on Mylar, a thin plastic sheet, but now are created on Catia, AutoCAD or other 3-D
graphic system.
A print is a copy of the drawing that shows what the object will look like when it is
completed. Regardless of the color, the terms “drawing”, “print” and “blueprint” all mean
the same thing when referring to copies of the engineering drawing. Prints provide you with
details like size and shape description, tolerances (allowable error) to be held, materials
used, finish, and other treatments.
Typical Print
Print reading is getting information from a print. This task involves visualization and
interpretation of the print.
Visualization is the ability to “see” or imagine the size and shape of the object from prints
that show views.
Top
3D view
Front
Side
The ability to interpret, or understand, the lines, symbols, dimensions, notes and other
information on the part is the other important part of print reading.
Some common lines, symbols, dimensions and notes
A print is the drawing of an object, but there is not enough information on a print to accurately
create the part. You also need the parts list, and reference information.
Picture sheet:
The picture sheet shows:
•
What the part looks like
•
Size and shape of the parts
•
How the parts ands assemblies fit together
•
Where the parts and assemblies are installed
The picture sheet shows the part with enough views to completely describe the part. The part
is shown in a two dimensional (flat) view. Picture sheets contain dimensions, symbols, and
tolerances.
Parts list:
The parts list contains:
•
List of material- what you need to build the part
•
General notes/Flag notes – more information on how to build the part
•
Part marking and finishing information
flag note 3
•
List of specifications- other documents that tell you how to install fasteners,
paint, part mark, etc...
Rev B
Reference Information:
Spacely
Specifications
Sprocket
For
C
Reference information includes:
Spacely
Parts List
Sprockets
Traveler
Work order/traveler
How to
Astro
-3
Sprocket
120 Cut…
build -3
Customer specifications
Finish
Picture sheet
Parts List
Reference
The Definition of Lines
On aerospace drawings, 9 types of lines are commonly used. Each has a particular meaning to
the engineer, and a skilled worker must recognize and understand the meaning of the lines to
correctly interpret the print.
1. Visible line: the visible line is a thick continuous line that represents all edges and surfaces of
an object that are visible in that view
__________________________________________________________
2. Hidden line: hidden lines have short dashes, and are used to show edges, surfaces and
corners not visible in a particular view.
Center lines
Visible lines
Front view
Hidden lines
Side view
3. Center line: center lines are a thin line with one short dash between two long
dashes. They are used to show the centers of holes, arcs, and symmetrical parts
(symmetrical means both sides are identical). Sometimes you will see the symbol CL,
or to designate a centerline, and SYM to tell you the part is symmetrical around the
centerline.
SYM
4. Dimension line: dimension lines are thin lines that have arrows on both ends, and a
dimension, or measurement, in between.
5. Extension line: an extension line is a thin line, used to place a dimension away from
the part, to make it easier to read
6. Leader line: leaders are thin lines with one arrow that point to an area, and give specific
information about that area.
Extension Line
Dimension
Leader
7. Cutting Plane lines/Section View lines: the cutting plane is a thick line, often with a 90°
bend, that ends with an arrow. They are used in pairs, when we need to “cut” a part open to
see more detail. The arrows indicate the direction your eyes are looking. On Boeing prints,
each section view is named; for example, 1A2C4, which means this is the first section cut in
zone A2, and the section view is located in zone C4.
1A2C4
Name 1A2 C4 address
Cutting Plane/
Section View Lines
Section line
1B6A3
Typical Section View
1B6
Section View Example
4
3
2
1
RevNew
D
1D3A2
D
1C3C2
C
C
1C3
B
B
-5
Bracket
A
1D3
4
3
2
PCM
The -5 is located in zone B3.
Section cut 1C3C2 is the first cut in zone C3, and the view is located in zone C2. The
name of the view, “1C3”, stays with the view.
Section cut 1D3A2 is from zone D3, and the view is located in zone A2.
8. Reference line: a thin line with two dashes. Reference lines are used to show alternate
position, adjacent parts, or repeated detail.
REF
65B4567-3
Alternate Position
Adjacent part
Repeated Detail
9. Break lines: break lines are used to show that there is more to the part than is being shown.
Some break lines are wavy lines, some are angular lines.
Orthographic Projection
After completing this chapter, you will be able to:
Identify an orthographic projection drawing
Identify objects shown in an orthographic projection drawing
See how the three standard views can describe a part.
The purpose of a drawing is to show the size and shape of an object, and to provide
certain information on how it is to be made. The best way to show every feature of
a part in its true size and shape is to use a multi-view orthographic projection
drawing. Aerospace drawings often use three views of a part, and these views are
drawn so that every feature can be seen and dimensioned. On some newer prints,
there is an isometric (3D) view of the part in the upper right corner of the drawing.
These not-to-scale views are to help you “see” the part. Isometric drawings really
help you understand what the part or assembly is to look like, but they can’t be
accurately dimensioned.
The different views on an orthographic projection drawing are arranged in a
systematic way so the print reader may mentally connect them together and
form an image.
Top
Isometric view
3D
Front
Side
Orthographic view
2D
The views of an orthographic drawing are
projected at right angles to each other, and
have a definite relationship. One way to
visualize the relationship between views is to
imagine that the part being placed in a glass
box, and only one side of the part can be seen
at a time. You can “see” where the surfaces in
one view will show as lines on another views,
and how holes in one view can be shown with
hidden lines in other views.
When the part is placed in the glass box, there
are six possible views- top, front, right side,
left side, bottom and rear. Usually a part can
be described in three views, so the views most
often used on orthographic drawings are top,
front, and right side.
Some parts, usually round shaped parts, can be shown in two views, since two of the views are
identical.
Top
Front
Orthographic view, 2D
Right
Side
Isometric view,3D
When you look at a multi-view drawing, here are some steps that might help in visualizing the
actual part:
•
Scan briefly all the views shown
•
Study the front view for shape description
•
Move from the front view to the other views and look for lines that describe the
intersections of surfaces, the limits of a surface, or the edge view of a surface
•
Study one feature at a time, looking at each view, and begin to picture in your mind
the shape of the real object
Being able to link the 2D views into a 3D image in your mind takes practice. Don’t be
discouraged if you need to sketch pictures, or break the part into simple geometric shapes
before you can visualize how the views of the drawing will result in an actual part.
Picture sheet scale
Some parts are so large they won’t fit on a drawing sheet, even a big drawing sheet. And some
parts are so small; you would need a magnifying glass to see them.
To help you figure out what the part needs to look like, the “scale” of the drawing is important.
Scale is the relationship between the actual size of the part to the part shown on the print.
Large parts may be drawn half size (scale ½), so they will fit on the drawing sheet. Small parts
can drawn at twice size (scale 2/1), so you can see every detail. Most aerospace prints are
drawn full size- for every inch on the part; there is an inch on the drawing. Some drawings may
have views that are drawn at different scales. Any view that is not drawn at full size (scale 1/1)
will have a note underneath, calling out the scale. The scale callout in the title block will also
give you this information.
The called out dimension is not affected by the scale.
PCMs are always drawn full size.
Full Size
2.5
Scale: 1/1
Twice Size
2.5
Scale:
2/1
Half
size
2.5
Scale:
1/2
Examples of scale callouts:
Scale Type
Scale Callout
View not to scale
Scale: None
Full
1/1
Reduced
½, ¼, 1/10
Enlarged
2/1, 4/1
Multiple
Noted, 1/1 & Noted
2782.2
231’ 10.2”
Airplanes, houses, and buildings are drawn smaller than they are, so you can see the whole
structure on one piece of paper.
.100
4 inches = 1 inch
Computer chips are drawn larger than they are, to show all the details. The dimensions are
accurate, just the picture is larger.
Drawing Notes and Symbols
Sometimes you need more information to build a part then just dimensions. Notes are often on
drawings to provide you with more details for a part or a process. Most of the notes that used
to be located on the picture sheets have been moved to the Parts List, but some notes are still
essential on the picture sheet.
There are two types of notes; general notes which can apply to the entire drawing, or just to a
specified area, and flag notes which are shown by a symbol
and apply only where they
are called out.
Examples of general drawing notes:
125 RA micro inches or better surface finish
Typical fillet except as noted
Flag notes,
are used on the face of the drawing to avoid repeating
information. They generally use numbers to tell them apart. To find out what a
particular flag note means, you look in up in the Flagnotes- General Notes section of
the Parts List.
Examples of flag notes:
Examples of flag notes:
On the picture sheet
Notes are in Parts List
Symbol
found on DWG
Definitions of Flagnotes-General
are located in Parts list.
1
FL 1 This area finished with F-17.33
6
FL 6 Shim gap in excess of .03
Common symbols
T
is a Tool Hole, a 0.247-0.250 hole used by Manufacturing
H
G
C is a PCM Grid Check point
Ø
means diameter, the distance across a hole
R
means radius, the distance from the center to the edge of the hole
F/P
means flat pattern
Is a fastener symbol, where a rivet or bolt will be installed.
Is a hole location for a fastener. This diameter will always be in 32nds.
TYP
means Typical, that the callout will be the same in several places
Dimensions and Tolerances
Most major industries do not manufacture all of the parts and sub- assemblies required in their
products. For instance, there are 3 million parts in a Boeing 777, provided by more than 900
suppliers. Frequently these parts are manufactured by specialty industries, to specifications
provided by the major industry. The key to successful operation of the various parts and subassemblies in the major product is the ability of two or more nearly identical duplicate parts to be
used in an assembly and function satisfactorily.
Here are some standard terms used on and about prints.
Tolerance is the amount of variation permitted from the design size of a part.
Tolerances can be shown by the variations between limits,
1.525- 1.530
as the dimension size followed by the tolerance,
1.455 ± .002
and when one tolerance value is given (the other is assumed to be zero)
1.825 + .003
On a print, if a dimension does not have a tolerance next to it, use the tolerance called out next to
the title block. If a dimension does have a called out tolerance, you must use that tolerance.
Decimal Place Value
1. 2 3 4 5
The numbers to the left of the decimal are whole numbers. The numbers on the right side of
the decimal are fractions of a whole number.
1.25 could be said as “one and a quarter inch”, or “one point two five”, or “one and twenty
five hundredths”.
5.389 could be said as “five and three hundred eight-nine thousandths”.
Types of Dimensions
Linear dimensions on aerospace drawings are given in inches and decimal fractions.
For example:
5.390
Angular dimensions are used on prints to indicate the size of angles in degrees (°), and the
fractional parts of a degree; minutes ( ´ ) and seconds ( ´´ ). A complete circle contains 360 °
(degrees), one degree contains 60 ´ (minutes), and one minute contains 60´´ (seconds).
25° 40´
25° 30´ ± 10´
25° 20´
Callout on print
Tolerances applied
Reference dimensions are occasionally given on drawings for reference and checking
purposes. These dimensions are followed by the word REF. They will be without tolerance,
and are not to be used for layout, machining or inspection operations.
1.25
1.35
2.60 REF
Tabular dimensions are used when a company manufactures a series of sizes of a part.
Dimensions on the drawing are replaced by reference letters and a table on the drawing lists
the corresponding dimensions.
Part No.
A
B
C
D
E
F
-202
-203
-205
.625
.750
.875
1.00
1.250
1.437
1.312
1.812
2.062
.156
.484
.562
.875
1.00
1.125
.250
.312
.375
ØF
ØB
E
D
C
A