Post on 05-Apr-2017
transcript
Introduction to Sectional Views
ENGINEERING DRAWING-IDWG-101
Aamir Naveed
Lecture # 5
Sectioned Drawings
A multi-view technical drawing that reveals details about internal features by displaying the part as if cut by an imaginary cutting plane
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
The Cutting Plane
An imaginary plane that defines where the object is cut
Shown in drawing adjacent to the sectioned drawing Arrows at the end of the cutting plane line indicate
the direction of view for the sectioned drawing The arrows point toward the part of the object that is
visible in the sectioned drawing. A sectioned drawing follows the general rules of any
view in a multi-view drawing
The Cutting Plane
The Cutting Plane
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
The cutting plane line takes precedence over center lines
Occasionally cutting plane lines are not shown when their location is obvious
The Cutting Plane
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
Section Lines
Section Lines
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)
Section Lines
Section Drawing Types
Full Section Half Section Assembly Section Offset Section Broken-Out Section Revolved Section Removed Section Special Section Conventions
Full Section
The cutting plane passes completely through the part as a single flat plane
Half Section
The cutting plane only passes half way through the part
The other half is drawn as usual
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
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
Assembly Section
Cut each part of the assembly and section each part with the appropriate section line type
Put the parts together in their assembled position
Assembly Section
The shaft is not sectioned because it is a standard part and section lines would provide no additional information
The other two part are made from the same material
The orientation of section lines clearly shows the location of the different parts
Assembly Section
The top and bottom mating part are made from different materials in the part shown below
A center line is added to the shaft to show that it is a circular feature
Offset Section
The internal features of many part can not be shown using a single straight cut to create the sectioned drawing
An offset section is used for such parts
Offset Section
The multi-view drawing is often difficult to interpret when there are several hidden features on the object
Look at the figure in your text and try to picture the part in your mind
A sectioned view makes the object much easier to understand
Offset Section
An offset section allows the cutting plane to pass through all of the internal features
There may be several bends in the cutting plane
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
Offset Section
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
Broken-out Section
Only a portion of the view is sectioned
A jagged break line is used to divide the sectioned and un-sectioned portion of the drawing
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
Removed Section
Similar to the revolved section except that the sectioned drawing is not superimposed on the drawing but placed adjacent to it
The view and the cutting plane are labeled (Section A-A)
The removed section may be drawn at a different scale
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
Special Section Conventions
The object is difficult to understand using standard multi-view drawings where hidden lines are used to represent internal features
Special Section Conventions
If the part is sectioned as it would actually appear if cut the details of the ribs and holes would not be clear
Since the objective is to make the drawing easy to interpret the drawing is modified following standard conventions
Special Section Conventions
The cutting plane shows that the features are revolved to their true radial position
Hidden features are not shown The sectioned drawing produced
is a distorted but clearer picture of the object
The section drawing appear as a full section
The arrows show the direction of the view
Special Section Conventions
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
Special Section Conventions
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