Engineering Drawing: Chapter 09 section


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Engineering Drawing: Chapter 09 section

  1. 1. Chapter 8 Section Views
  2. 2. Contents Introduction Basic components Kind of sections Dimensioning
  3. 3. Introduction
  4. 4. Given Necessity of a section view Finish No Internal features make a view difficult to read or dimension? Orthographic projection principle Yes Section technique Orthographic projection principle
  5. 5. Purposes Clarify an internal feature. Facilitate dimensioning. Example Regular view Section view
  6. 6. Basic components
  7. 7. Cutting plane Cutting plane is an imaginary plane that cuts through the object. Location and direction of a cutting plane depend on a hidden feature that is needed to be revealed. A section view is obtained by viewing the object after removed the cover up part in the direction normal to the cutting plane. Cutting plane Example Section view Basic Components
  8. 8. Cutting plane line In an orthographic view, a cutting plane is presented as a “ cutting plane line, CPL ” and is drawn in either of an adjacent view of the section view. Given Direction 1 Direction 2 Direction 3 Section view CPL CPL Section view Section view
  9. 9. Viewing direction Cutting plane line : Line styles The cutting plane line is presented by a chain line. (This course) Begin and end the line with a short visible line. When the line changes its direction , draw a short visible line at that corner. Draw an arrow at about the mid-length of a short visible line, the arrow head is pointed toward to this line in a viewing direction. Examples 1 2 3 Basic Components
  10. 10. Class activity Do you find something wrong in the following cutting plane lines? Yes No Right! Wrong! (The arrow on the right side should be pointed downward) Yes No Right! Wrong! (The arrow head have to touch the short visible line) Yes No Right! Wrong! (Because the cutting plane line used in this course is a chain line ) 3 1 2
  11. 11. Class activity Change the following incorrect cutting plane line style to that previously suggested. 1 2
  12. 12. Section lining : Purpose Section lines or cross-hatch lines are added to a section view to indicate surface that are cut by a cutting plane. Examples Section view without section lines Section view with section lines Visible surfaces and edges behind the cutting plane are drawn in a section view.
  13. 13. The section lines are different for each type of material. Cast iron, Malleable iron Steel Concrete Sand Wood Practically , the cast iron symbol is used most often for any materials. Section lining : Symbol Examples
  14. 14. The spacing between lines may vary from 1.5 mm for small sectioned areas to 3 mm for large sectioned areas. Poor practices Section lining : Recommended practice 1 Too dense Too coarse Uneven spacing Uneven orientation Examples
  15. 15. It should not run parallel or perpendicular to contour of the view. Section lining : Recommended practice 2 Poor practices Examples
  16. 16. Section lining : Special case When the sectioned area is large, an outline sectioning may be used to save time. Example Basic Components
  17. 17. Class activity Freehand sketch a section lines. 1 2
  18. 18. Class activity Which one is a good practice in section lining? 1 2
  19. 19. Kinds of section
  20. 20. Kind of sections 1. Full section 2. Offset section 3. Half section 4. Broken-out section 5. Revolved section (aligned section) 6. Removed section (detailed section)
  21. 21. A skill requirement 1. Ability in orthographic visualization 2. Understanding in a conventional practice for each kind of sections. (You will learn about them from now on.)
  22. 22. Conventional practice : Treatment of a hidden line Hidden lines are usually omitted within the section lined area. Example Hidden lines are omitted . Hidden lines present.
  23. 23. Full section : Concept & example A section view is made by passing the straight cutting plane completely through the part. Example
  24. 24. A closer look Kinds of sections
  25. 25. Offset section : Concept & example A section view is made by passing the bended cutting plane completely through the part. Example Edge views of the cutting plane are omitted Kinds of sections
  26. 26. Half section : Concept & example A section view is made by passing the cutting plane halfway through an object and remove a quarter of it. Example Kinds of sections
  27. 27. Half section : Conventional practice A center line is used for separating the sectioned half from the unsectioned half of the view. Hidden line is omitted in unsectioned half of the view. Kinds of sections
  28. 28. A section view is made by passing the cutting plane normal to the viewing direction and removing the portion of an object in front of it. Broken-out section : Concept & example Example Kinds of sections The sectioned and unsectioned portions are separated by a break line. Cutting plane line is not necessary. Break line is freehand drawn as a thin continuous line ( 4H ). Conventional practices
  29. 29. Revolved section : Concept & example A section view is made by revolving the cross-section view 90 o about a cutting plane line and drawn on the orthographic view. Example a a b b
  30. 30. 1. Superimposed to orthographic view. Superimposed Break 2. Break from orthographic view. Revolved section : Placement of a cross-section view
  31. 31. Revolved section : Additional example Kinds of sections
  32. 32. 6. Removed section Removed section is created with the same concept as a revolved section. But, the cross-section view is shown outside the view. Removed section : Concept
  33. 33. Example : Revolved vs. removed sections. Revolved section Removed section Removed section : Comparison with a revolved section
  34. 34. Example : Situation that removed section is preferred. Removed section : Advantage Removed section technique can improve a reading of the orthographic view. Example Revolved section Removed section
  35. 35. Section A–A Section B–B A single or multiple removed (cross) section view(s) can be arranged without aligning with the cutting plane line, but it have to be labeled name of the cutting plane line. Removed section : Alternative placement of a view Example Kinds of sections A A B B
  36. 36. Summary Drafter has several choices of section techniques to reveal an internal feature of an object. Object having a symmetry, an appropriate choice is such as full section or half section. Object having several features that do not locate in-line among each other, an offset section may be a good choice. Broken-out section is usually used when a drafter need to reveal a local detail of each feature. Revolved and removed section views are efficient when a drafter need to reveal only a cross section shape of an object. Kinds of sections
  37. 37. Comparison of a different section techniques
  38. 38. Dimensioning
  39. 39. Dimension techniques Dimensioning of the section views follows the typical rules of dimensioning. For a half-section view, use dimension line with only one arrowhead that points to the position inside the sectioned portion.  50 10  50
  40. 40. Dimension techniques Avoid placing dimensions or notes within the section lined area. If the situation is unavoidable, omit the section lines in the area of the note.