Lesson Seventeen

1. Lesson Seventeen Section views 1. Introduction Sectional views, often called sections, provide a method of showing the interior details of an object that are difficult to visualize from hidden lines in exterior views.

2. 2. Draw section view. The steps for drawing section are as follows. Step 1: Cut. Step 2: Remove Step 3: Project Step 4: Draw section lines（画剖面线） Step 5. Label (标注)

3. Take the preceding object for example. Top view is a view. And now, front view need to be drawn into section view.

4. Step 1: Cut — A cutting plane is supposed to pass through the object. In general, a cutting plane passes through the symmetric plane of an object and is parallel to or perpendicular to a certain principal projection plane. In the problem, the cutting plane is a frontal plane and it passes through symmetric plane of front and rear.

5. Step 2: Remove — When the portion of an object between the viewer and cutting plane is removed, the interior details are exposed.

6. Step 3: Project — the spare (剩下)portion is projected to V projecting plane. Note that all visible lines, edge lines and convergence lines, should be drawn and any visible line should not be missed.

7. Step 4: Draw sectional symbol（画剖面线）— draw section lines in solid parts (实体部分).The metal material section lines are 45° oblique lines and thin lines parallel to each other.

8. Open out:

9. Step 5. Label (标注) — The label of a section view has four items. ① sectional plane symbol（剖切面符号）: sectional plane symbol is double thick line (双倍的粗实线) and represents cutting position. Draw two segments cutting plane symbol at where start and end. ② Name for section plane ② Arrows (箭头)：Arrows indicate the direction of projection. The arrows are always perpendicular to the cutting plane symbol. ③Name for section view: Near the cutting plane symbol, write any capital letters. And above section, we write the corresponding capital letters .

10. For example:

11. Note : 1) Because cutting is imaginary, when a certain view is drawn into section, the other views yet are full and may be drawn into section. 由于剖切是假象的，所以当某一个视图画成剖视图后，其它 视图是完整的，而且其它视图还可以取剖视图。 2) In general, there are no dashed lines in section. Namely, all dashed lines in the section are omitted unless representation is not clear. 一般情况下，剖视图中无虚线，除非没有虚线就不 足以表达清楚的情况下才使用虚线。 3) When there is only a single cutting plane and it passes through symmetric plane of an object, labeling is omitted fully.

12. For example, the labeling of the section is omitted fully.

13. For example, when front view is drown into section, all dashed lines are omitted. All dashed lines mean dashed line in the section and in the top view and left view.

14. For example, the dashed lines in the front section should be reserved as it represents the shape of rear boss.

15. For example, top section must be labeled as there is no symmetric plane on the solid of upper and down. Note that two arrows are omitted.

16. 3. Kinds of section According to more or less of internal structure represented by section, sections may be divided into three kinds which are full section, half section and broken-out section. 3.1 full section (全剖视图) A full section view is one in which the cutting plane passes entirely across the object, so that the internal structure is complete. The preceding sections are full section.

17. 3.2 Half section view (半剖视图) This is a view sometimes used for symmetric objects in which one half is drawn in section and the other half as a exterior view. The cutting plane is imagined to extend halfway across, then forward and remove a quarter, so that the internal structure only is a half. A half section has the advantage of showing both the interior and exterior of the object on one view without dashed lines

18. For example, front view and top view are given and draw into half section.

19. If front view is drawn into full section, then exterior structure is not represented.

20. If view is taken a half and section is taken a half to combine front view, then front view is half section.

21. Look at figure please.

22. Top view is B – B half section which rear half part is view and front half part is section.

23. Note particularly that a center line separates the exterior and interior portions on the half section That is to say, the separated line between view and section is a center line.

24. For example, front view and left view are half section. The circle is dashed circle on the front view, so being omitted.

25. 3.3 Broken-out section Only a certain interior structure of an object needs to be revealed, and this can be accomplished with a broken-out section. The section view and the external view are separated by a wave line. Wave line represents projection of a broken surface of an object. Only when the cut portion is revolutionary solid, the section view and the external view are separated by a center line.

26. For example 1:

27. Note that if there is only one cutting plane and cutting position is obviously, then labeling may be omitted on broken-out section. Note that wave line can not be coincided with other line. Note that wave line can not extend out section and there is no wave line in hole, as where there are not material.

28. For example 2:

29. For example 3: Wave lines

30. For example 4:

31. For example 5: Front view of the object disagree to adopt half section as there is a thick line on the symmetric plane. But fit to adopt broken-out section. It means wave line.

32. For example 6: Judge incorrect or correct for broken-out section. Incorrect Correct

33. For example 7: Correct errors for broken-out section. ×

34. Exactitude answer:

35. For example 8: Correct errors for broken-out section.

36. Answer:

37. For example 10: Only when the cut portion is revolutionary solid, the section view and the external view are separated by a center line. Wave line is substitute by Center line in revolution.