4. OBJECTIVES
TECHNICAL
DRAFTING
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1. Identify signs, symbols and data according to job specifications.
2. Determine signs, symbols and data according to classification.
3. Value the importance of signs and symbols in technical
drafting.
6. DRAFTING AS A LANGUAGE
TECHNICAL
DRAFTING
8
• Drafting is also known as the “language of industry”
• Industry uses this precise language because the
drawings must communicate the information the
designer had in mind to those who produce the
product.
7. DRAFTING AS A LANGUAGE
TECHNICAL
DRAFTING
8
Drafting is called a “universal language”
• Symbols (lines and figures) have specific meaning
are used.
• The symbols accurately describe the shape, size,
material, finish, and fabrication or assembly of a
product.
8. INTRODUCTION TO THE
ALPHABET OF LINES
Line symbols used in technical drawing are often
referred to as ALPHABET OF LINES. The use of line
symbols enables engineers/designers to express features of
designed products clearly and accurately. Line features vary
not only by width but also by how they are graphically
represented in a drawing.
9. INTRODUCTION TO THE
ALPHABET OF LINES
• Each line has a definite form and line weight.
• The standard thick line weight is 0.6mm HB Lead.
• The standard thin line weight is 0.3mm HB Lead.
• The standard construction line weight is 0.5mm 2H
Lead.
10. LINES
Hidden Line
Center Line
Dimension Line
Extension Line
Leader Line
Cutting Plane
Section Line
Phantom Line
Border Line
Break Line
Visible Line
Main Line Types
Reference Line
11. VISIBLE LINES/
OBJECT LINES
1
• Dark, heavy lines.
• Used to outline the exterior contour of the
object being drawn.
• Define features you can see in a particular
view.
0.6mm HB Lead.
12. HIDDEN LINES
2
• Light, narrow, short, dashed lines.
• Medium weight line used to describe edges which are
not visible to the eye.
• It is also used to indicate the hidden intersection of
planes and other hidden features of the object.
_ _ _ _ _ _ _ _ _ _ _ _
13. CENTER LINES
3
• These are thin broken lines used to indicate the
axes of all symmetrical objects or features, both
circles, and paths of motion
• These are the lightest or finest lines in drawing.
These consists of one long and one short dash
alternatively drawn
14. DIMENSION LINES
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• This is used to indicate the measurements of an
object. It is light in weight and broken in the
middle to provide space for dimensions. It
consists of three parts; arrowheads, fine line, and
number of measurements.
15. EXTENSION LINES
5
• This is a continuous line extending from a view to indicate the extent of
measurement given by a dimension line that is located outside the view.
• It is slightly heavier than a center line and is composed of long equal dashes about
7mm to 4cm long and with gaps for about 1 to 2mm.
16. REFERENCE LINES
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• This is an irregular fine, curved line with an
arrowhead at one end. It is used to label the parts of an
object.
17. LEADER LINE
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• This is a fine, broken line with an arrowhead at one
end. The broken line usually consists of a short
horizontal line and an inclined line drawn at any
convenient angle.
• This is also used for indicating the measurement
and name of a part of an object.
18. BREAK LINES
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• - this is a medium line used to
break an object when it is too
large to get on the drawing paper.
19. CUTTING PLANE LINES
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• This is a heavy broken line drawn across an
object to show a sectional view. The
arrowheads indicate the direction in which the
section is to be seen.
• A sectional view is used to describe the interior
construction of the object.
20. BORDER LINES
10
• This is the heaviest or darkest line in
a drawing. It surrounds a drawing
and is rectangular in shape.
21. PHANTOM LINES
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Thin lines made up of long dashes alternating with
pairs of short dashes.
Three purposes in drawings.
1. To show the alternate position of moving parts.
2. To show the relationship of parts that
fit together.
3. To show repeated detail.
22. SECTION LINES
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• Thin line is usually drawn at a
45-degree angle and indicates the
material that has been cut through
in a sectional view.
Section Line
23. VISIBLE LINE
LEADER LINE
HIDDEN LINE
DIMENSION LINE
EXTENSION LINE
CENTER LINE
BREAK LINE
PHANTOM LINE
CUTTING PLANE
LINE
SECTION LINE
BORDER LINE
REFERENCE LINE
24. CUTTING PLANE LINE
EXTENSION LINE
VISIBLE LINE
CENTER LINE
BREAK LINE
PHANTOM LINE
HIDDEN LINE
DIMENSION LINE
SECTION LINE
LEADER LINE
REFERENCE LINE
1
2
3
4
5
6
7
8
9
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25. REVIEW
• Why is drafting considered a universal language?
Even though people around the world speak different
languages, the graphic language (symbols & line types) has
remained common.
26. REVIEW
• Why is it important to recognize the alphabet of
lines?
• The lines in the Alphabet of Lines are used to describe
shape, size, hidden surfaces, interior detail, and
alternate positions of parts.
• Each conveys a particular meaning on the drawing.
