Download - Lect 5. sectiong
Engineering Graphics
SECTIONED DRAWING/VIEW
Sectioned Drawings/Views
Definition
A multiview technical drawing that reveals details aboutinternal features by displaying the part as if cut by an imaginarycutting plane
A sectional view is used to expose the internal features of anobject.
Since the sectioned drawing shows internal features there is generally no need to show hidden lines
Especially helpful for assembly drawings
To demonstrate the use of section views which showinternal features of objects that are not easilyunderstood in standard multiview drawings
To be able to generate section views
To make the drawing more understandable,especially the internal details of the part
Objectives
Sectioned Drawings/Views
Outline
Cutting Plane
Section Lines
Types of Section Drawings
Example (class work)
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 multiviewdrawing
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
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 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)
Materials – Common materials
The symbol for cast iron can be used for most section views.
Refer to any drafting text for additional symbols.
Section Lines
Section Lines Cont.
Section lines or hatch patterns are standardized in many disciplines.
The adjacent chart showsthe most common materialtypes and associated hatch patterns.
Care must be taken to avoid hatch pattern angles similar to those of the drawn object as seen (adjacent chart)
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 waythrough the part
The other half is drawn as usual
Hidden lines are not shown on either halfof the part
A center line is used to separate the twohalves
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
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
Offset Section
The multiview drawing is often difficult to interpret when there are several hidden features on the object
Look at the Fig. on theL.H.S and try to picture the drawing 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 unsectioned portion of the drawing
Broken-Out Section
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 multiview 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
THANK YOU
class workUse free hand sketch to draw out the section A-A