sectional views and conventions
DESCRIPTION
Engineering drawing and graphics lab,TRANSCRIPT
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SECTIONAL VIEWS AND CONVENTIONS
1. PURPOSE OF SECTIONAL VIEWS
• To see the inner details of an object.
• Sectional views help in clarifying the interior shape of a part because in the outer view too many hidden lines can create confusion.
• To sometimes see small cross sections of a part.
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Hidden Lines in the Front View create confusion in the understanding of the shape of part.
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The sectioned Front View clearly shows the internal part shape.
AA
SECTION A-A
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2. HOW SECTIONS ARE SHOWN
• The place from which the section is taken shall be clearly identified.
• A cutting plane, directional arrows and identification letters shall be used.
• A sectional view must show which portions of the object are solid material and which are spaces by drawing section lines in the solid parts.
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3. TYPES OF SECTIONS
A. Full Section
• The cutting plane shall pass entirely through the solid.
• The cutting plane may cut straight across or change direction to pass through features to be shown.
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A full section with the cutting plane passing straight across.
A
A SECTION A-A
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A full section with the cutting plane changing direction
• Change in plane direction shall never be shown in the sectioned view.
A
A SECTION A-A
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B. Half Section
• The cutting plane passes through one half of the solid.
• Used for symmetrical solids.
• One half of the solid is sectioned while the other half is the regular exterior view.
• Advantageous in the fact that both interior and exterior can be shown without drawing hidden lines.
• Difficult in dimensioning
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A
ASECTION A-A
• In a half section, hidden lines are usually not shown in the exterior half.
• The two halves in the sectioned view are separated by a center line.
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A
ASECTION A-A
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C. Broken-Out Section
• To be used where an interior portion must be shown but a full or half section cannot be used because the cutting plane would remove some feature that must included.
• An irregular break line is used to limit the extent of the section.
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D. Rotated Section
• Used for showing cross sections of parts while saving space.
• Section is drawn on the view by rotating the section at 90o.
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E. Removed Section
• Used for the same purpose as rotated section but the section is removed and placed adjacent to the drawing of the part.
• The cutting plane with reference letters shall be mentioned.
A
SECTION A-A
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F. Auxiliary Section
• Conforms to the principles of orthographic projections.
• Used to show section of an inclined feature.
• All types of section, i.e., full, half, broken out, rotated and removed are used.
A
A
B
B
SECTION A
-A
SECTION B
-B
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4. DRAWING PRACTICES FOR SECTIONAL VIEWS
A. Unnecessary Hidden Detail
• Hidden edges and surfaces are not shown behind the cutting plane.
B. Visible Detail
• Visible edges and surfaces shall be shown behind the cutting plane.
• Shall be omitted only if the section is to be emphasized on.
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Visible Edges shown (Recommended)
Visible Edges not shown (Not recommended)
A
A
SECTION A
-A
Visible Edges not shown (Recommended)
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C. Section Lining
• A pattern of lines shall be used to fill the areas of the solid material cut by the section plane.
• Usually at 45o to part’s principal surfaces, but other angles such as 15o, 30o, 60o and 75o can also be used.
• Section lines shall be thin and fine lines and shall be equally spaced.
• Direction and/or spacing of section lines shall be changed for adjacent parts.
• Various patterns are sometimes used for different materials.
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5. PARTS NOT SECTIONED
• Parts that are more easily recognized by their exterior are not sectioned.
• Bolts, nuts, screws, studs, pins, keys, cotters, rivets etc. are all fasteners and therefore shall not be sectioned. Shafts shall also not be sectioned unless inner details are required.