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PREPARED BY: NOR HELYA IMAN KAMALUDIN helya@unimap.edu.my
LECTURE 6: SECTIONING PREPARED BY: NOR HELYA IMAN KAMALUDIN PTT 105: Engineering Graphics
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Several Types of Section Drawings
OUTLINE… Cutting Plane Section Lines Several Types of Section Drawings PTT 105: Engineering Graphics
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Purpose of Sectioning PTT 105: Engineering Graphics
To demonstrate the proper use of section views which show internal features of objects that are not easily understood in standard multiview drawings To demonstrate the use of CAD tools in generating section views PTT 105: Engineering Graphics
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Sectioned Drawings Definition: A multiview technical drawing that reveals details about internal features by displaying the part as if cut by an imaginary cutting plane. Objective: To make the drawing more understandable, especially the internal details of the part. Since the sectioned drawing shows internal features there is generally no need to show hidden lines. Especially helpful for assembly drawings. PTT 105: Engineering Graphics
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The Cutting Plane An imaginary plane that defines where the object is cut Shown in drawing adjacent to the sectioned drawing Drawn with the PHANTOM line type Arrows at the end of the cutting plane line indicate the direction of view for the sectioned drawing. Cutting Plane PTT 105: Engineering Graphics
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The Cutting Plane (cont’d)
The cutting plane line takes precedence over center lines Occasionally cutting plane lines are not shown when their location is obvious Cutting planes may be labeled at their endpoints if multiple cutting plane lines are used When using multiple cutting planes each sectioned drawing is drawn as if the other cutting plane lines do not exist PTT 105: Engineering Graphics
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Section Lines Section lines are drawn where the object passes through the cutting plane. If a saw was used to cut the part then section lines represent the cutting marks left by the saw blade. Different materials may be represented by the use of different section line types. The general section line type which may be used for any material is the line type for iron. PTT 105: Engineering Graphics
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Section Lines (cont’d)
Section lines should not be parallel or perpendicular to object lines Section lines are generally drawn at 45 degrees unless this conflicts with other rules Section lines should be oriented at different angles for separate parts Occasionally section lines are only drawn on the perimeter of large areas Section lines are not used for thin parts rather they are filled in solid (Do not use closely spaced section lines) PTT 105: Engineering Graphics
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Section Drawing Types Full Section Half Section Assembly Section
Offset Section Broken-Out Section Revolved Section Removed Section Special Section Conventions PTT 105: Engineering Graphics
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Full Section The cutting plane passes completely through the part as a single flat plane. PTT 105: Engineering Graphics
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Half Section The cutting plane only passes half way through the part
Hidden lines are not shown on either half of the part A center line is used to separate the two halves Mostly used on cylindrical parts PTT 105: Engineering Graphics
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Assembly Section Shows how parts fit together
Different parts have different section line orientation Different materials use different section line types Standard parts (shafts, pins, dowels, rivets, screws, washers, gears, etc.) are not sectioned PTT 105: Engineering Graphics
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Assembly Section (cont’d)
Steps in assembly section: Cut each part of the assembly Section each part with the appropriate section line type Put the parts together in their assembled position PTT 105: Engineering Graphics
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Assembly Section (cont’d)
Example 1: Consider the following object: The shaft is not sectioned because it is a standard part. The other two part are made from the same material. The orientation of section lines clearly shows the location of the different parts. shaft PTT 105: Engineering Graphics
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Assembly Section (cont’d)
Example 2: Consider the following object: The top and bottom mating part are made from different materials A center line is added to the shaft to show that it is a circular feature PTT 105: Engineering Graphics
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Offset Section In order to create the sectioned drawing, an offset section is used to show the internal features of many part that can not be shown using a single straight cut. PTT 105: Engineering Graphics
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Offset Section (cont’d)
The multiview drawing is often difficult to interpret when there are several hidden features on the object A sectioned view makes the object much easier to understand. PTT 105: Engineering Graphics
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Offset Section (cont’d)
An offset section allows the cutting plane to pass through all of the internal features There may be several bends in the cutting plane PTT 105: Engineering Graphics
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Offset Section The actual part would show a new visible line at the bend in the cutting plane Since the cutting plane bend is arbitrary, do not show the line representing this bend in the sectioned drawing PTT 105: Engineering Graphics
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Offset Section (cont’d)
The sectioned view does not show the bend in the cutting plane Hidden lines are not shown Be sure to include object lines that are behind the cutting plane PTT 105: Engineering Graphics
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Broken-Out Section Only a portion of the view is sectioned
A jagged break line is used to divide the sectioned and unsectioned portion of the drawing PTT 105: Engineering Graphics
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Revolved Section A cross section of the part is revolved 90 degrees and superimposed on the drawing A jagged break line may be used to divide the revolved section from the rest of the drawing PTT 105: Engineering Graphics
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Removed Section Similar to the revolved section except that the sectioned drawing is not superimposed on the drawing but placed next to it The view and the cutting plane are labeled (Section A-A) The removed section may be drawn at a different scale PTT 105: Engineering Graphics
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Special Section Conventions
There are special rules (conventions) that are followed to make some parts more understandable Some features are rotated to their true radial position in sectioned views PTT 105: Engineering Graphics
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Special Section Conventions (cont’d)
The object is difficult to understand using standard multiview drawings where hidden lines are used to represent internal features PTT 105: Engineering Graphics
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Special Section Conventions (Cont’d)
In order to make the drawing easy to interpret the drawing is modified following the standard conventions (rules). PTT 105: Engineering Graphics
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Special Section Conventions (cont’d)
The cutting plane shows that the features are revolved to their true radial position. Hidden features are not shown The sectioned drawing produced is distorted but clearer picture of the object is obtained. The section drawing appear as a full section The arrows show the direction of the view. PTT 105: Engineering Graphics
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Special Section Conventions (cont’d)
Ribs are not sectioned when the cutting plane passes through them lengthwise Ribs are sectioned if the cutting plane passes through them at other orientations Rib are sectioned Rib are not sectioned PTT 105: Engineering Graphics
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Special Section Conventions (cont’d)
The front view is replaced by a full section view The cutting plane shown in the top view shows the direction of the line of sight The holes and ribs have been revolved to their true radial position The ribs are not sectioned in this orientation The section lines are all drawn at the same angle since the object is one solid part Full section view (top view) Front view PTT 105: Engineering Graphics
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Sectioning With Solid Models
Slice Cuts the solid object at the specified cutting plane using the current color Breaks the objects into two parts One part may be deleted or moved Section Creates a 2-D drawing of the section Only draws the portion of the object that is cut (i.e. the portion of the object that has section lines) PTT 105: Engineering Graphics
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Sectioning With Solid Models (cont’d)
SLICE command SECTION command PTT 105: Engineering Graphics
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Sectioning With AutoCAD
Use BHATCH Use the correct scale Default line orientation is 45 degrees The general line type is ANSI31 Used: different line types for different materials different line orientations for different parts Use PICK POINTS to select an internal point in the sectioned portion of the drawing PTT 105: Engineering Graphics
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PTT 105: Engineering Graphics
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