1. Mechanical Engineering Drawing MECH 211/M
Lecture #10 SECTIONS-FASTERNERS- BEARINGS-SEALS
Dr. John Cheung

2. Sections

3. Outline Sectional views More sectional views in one drawing
Half sections
Threads and Assemblies in section
Offset section
Ribs, hoes and lugs in section
Revolved and removed section
Phantom lines

4. Sectional Views FULL SECTION Shows interior detail
Describes complicated parts
Eliminates the need for hidden lines
Frequently replaces a regular view
FULL SECTION

5. Sectional Views Full Section
A section view in which the cutting plane extends entirely through the object in a straight line

6. Sectional Views Sectional lining Also called crosshatching
Indicates surface that has been theoretically cut
Lining symbols may indicate the material that makes up the object

7. Sectional Views General Purpose Sectional lining Drawn with thin lines
To look for
Direction of section lines
Space for accommodating dimensions
Thin parts shown as thick lines
Drawn with thin lines
Lines are usually drawn at 45 to the object’s main outline
The same angle and direction is used for the whole ”cut” surface of a part
Large areas can be marked with section lining only around the outline

8. Two or more Sectional Views
If two or more sections appear on the same drawing:
Cutting-plane lines are identified by two identical capital letters
Sectional view subtitles incorporate the identification letters.
For clarity, should point to the right.
Avoid hidden line in section view

9. Half Sections Shows one-half of the view in section
Has two cutting planes perpendicular to each other
One quarter of the object is removed
Cutting line should continue

10. Threads in Sections Representation of threads in drawing
Detailed, Schematic, Simplified

11. Assemblies in Sections
Sectioning in assembly drawings
Section lining on assembly drawings
Shafts, Bolts, Pins, Keyseats
No section

12. Assemblies in Sections
Section lining in assembly drawings
Use opposite directions for section lining on adjacent parts
For more than two parts, use lining at a different angle

13. Assemblies in Sections
Section lining in assembly drawings
Avoid symbolic section lining on drawings to be microformed
If adjacent thin parts are filled in, leave space between them

14. Assemblies in Sections
Parts generally not sectioned:
Shafts
Bolts
Pins
Keyseats
Similar solid parts
A broken-out section of a shaft may be used to describe a key, keyseat, or pin.

15. Offset Sections
A cutting plane can be bent to include several surfaces

16. Ribs, Holes, and Lugs in Sections
Parts generally not sectioned:
Conventions for aligning ribs, holes and lugs in section

17. Ribs, Holes, and Lugs in Sections
Aligning and rotating
When a true projection would be misleading, the rib, hole or lug is revolved to show its true relationship to the part
Rib here

18. Revolved and removed Sections
Ribs, spokes, and arms

19. Revolved and removed Sections
Show cross-sectional shape of ribs, spokes, or arms
Section is rotated 90 degrees

20. Revolved and removed Sections
Revolved section:
Section may be superimposed on regular view of part
Regular view is broken if needed for clarity or to add dimensions
Removed section:
Removed to an open area on drawing; may be enlarged. Shorten object length.

21. Spokes and arms in Sections
Section lining is not drawn on parts that are
Not solid
Not continuous around the hub

22. Partial or broken out Sections
Partial sections are indicated with an irregular break line.
A cutting-plane line is not required.

23. Phantom or Hidden Sections
Used to show interior details of parts that are not symmetric, or mating parts in assembly
A phantom section is a sectional view superimposed on a regular view
The front portion of the object is not removed

24. Screws, Nuts and Bolts Used to assemble machine parts
Used to transmit power / motion
The threads are cut or rolled
Bolts and nuts must be matched

25. Screw and Thread Terminology
Major Diameter - The largest diameter of a screw thread.
Minor Diameter - The smallest diameter of a screw thread.
Pitch
Pitch diameter

26. Tap and Die

27. Thread Specifications – Imperial System
ANSI Y
Thread form
Thread series
Major diameter
Class of fit
Threads per inch

28. Screw Thread Forms
Unified thread is agreed as standard in US, Canada and Britain, the crest may be flat or rounded but the root is rounded. Otherwise similar to American national

29. Screw Tread Forms
ISO Metric is the most common of all. The depth is smaller than that of Unified National thread

30. Measuring Thread Pitch
Pitch is the distance along the axis between corresponding points in adjacent threads (i.e crest to crest or root to root)
Metric: Measured in millimeters (i.e. M10 X 1.5)
Imperial: Measured in threads per inch
Thread Pitch is measured with scale or a thread pitch gage

31. Thread Types
Series: Varies with the pitch and the major diameter of the thread
Coarse Series (UNC)
General purpose usage
Fine Series (UNF)
Used when a great deal of force is necessary
Extra Fine Series (UNEF)
Used when the length of engagement is short and there is a high degree of stress
8-Pitch (8UN), 12-Pitch (12UN), 16-Pitch (16UN)
Does not depend on the diameter

32. Metric Thread Series Simplified compared to Unified Series
Only two series
Coarse (General Purpose)
Fine

33. Simplified & Schematic Internal Symbols Normal & Section Drawings

34. Imperial Thread Notes

35. Basic Metric Thread Note

36. Screws, Nuts and Bolts

37. Large variety of bolts (dimensional, head shape, etc.)
Material, quality, finishing
Grade

38. Fastener Locking

39. Fastener Locking
Durlock nut
Castellated nut
Jam nut

40. Screw Types Head can have different shapes
Pass through a clearance hole to screw into member
Socket screws are used while in crowded condition

41. Non-Permanent Fasteners Snap Rings

42. Non-Permanent Fasteners Pins

43. Used to permanently fasten mechanical components

44. Common Riveted Joints

45. Blind Rivets

46. Welding
Joining of two part using a third component – filler that joins the parts when in liquid state
Soldering and brazing – low temperature binding materials – Sn-Pb, Cu-Ag alloys
Limited capability to face thermo-mechanical loading

47. Welding Very well regulated activity It requires license to practice
Welders bear significant responsibility
The activity is based on rigorous rules and regulations
Designer prescribe welding based on mechanics of materials calculations
Symbols indicate the type of welding

48. Basic Welding Symbols

49. Compression Springs Extension Springs Torsion Springs
Designed to store energy when deflected and return the same amount of energy when released
Basically divided as Helical and Flat springs
Helical springs are sub divided as
Compression Springs
Extension Springs
Torsion Springs

50. Helical Springs
Compression, Extension & Torsion

51. Spring Representation
Detailed representation
Schematic representation
Working drawing of a compression spring

52. Gears

53. Gear Representation
A table containing cutting data must accompany the representation

54. Ball Bearings

55. Ball and Roller Bearings

56. Antifriction Bearings
Bearing Symbols
Classified into simplified, pictorial and schematic representations
Simplified representation – used when not necessary to show the form or size of the rolling bearings or details of their inner design (A)
When it is desirable to show the functional principle of rolling elements, symbols for the appropriate rolling element and raceway surface are added (C)

57. Lubricants and Radial Seals
Radial Positive Contact Seals
Applies sealing pressure to mating cylindrical surface to retain fluids and to exclude foreign matter. Used for oscillating and reciprocating shaft motion.

58. Lubricants and Radial Seals
Seal Symbols
The simplified representation of seals (Fig ) recommended for use on drawings, wherever it is not needed to show the exact form and size of seals
Fig, Functional representation of seals