Section Views

1. Section Views Engineering Graphics Stephen W. Crown Ph.D.

2. Objective • 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

3. Outline • Cutting Plane • Section Lines • Several Types of Section Drawings • Examples of Homework Problems

4. 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

5. 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. 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 multiview drawing The Cutting Plane

6. 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

7. 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

8. 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)

9. Section Drawing Types • Full Section • Half Section • Assembly Section • Offset Section • Broken-Out Section • Revolved Section • Removed Section • Special Section Conventions

10. Full Section • The cutting plane passes completely through the part as a single flat plane

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. Offset Section • The multiview 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 • Use either drawing for your homework

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. Special Section Conventions • The object is difficult to understand using standard multiview drawings where hidden lines are used to represent internal features

26. 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

27. 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

28. 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

29. 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

30. 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)

31. SLICE command SECTION command Sectioning With Solid Models

32. Sectioning With AutoCAD • Use BHATCH • Use the correct scale • Default line orientation is 45 degrees • The general line type is ANSI31 • Use different line types for different materials • Use PICK POINTS to select an internal point in the sectioned portion of the drawing

33. Example