Fitter 1st year theory book notes hai aap log Threads and Fasteners.pdf

Good morning student today we show the screw thread and fasteners

1. Mechanical Drawing
(MDP 115)
FirstYear,
Mechanical Engineering Dept.,
Faculty of Engineering,
FayoumUniversity
Dr. Ahmed SalahAbouTaleb

2. Threads and Fasteners
Topics
Exercises
2

3. Threads & Fasteners: Topics
Summary
1)Fasteners
2)Screw Thread Definitions
3)Types of Thread
4)Manufacturing Screw Threads
5) Drawing Screw Threads
6) Unified Threads
7) Metric Threads
8) Drawing Bolts
9) Bolt and Screw Clearances
3

4. Threads & Fasteners: Exercises
Exercise 1: Screw thread features
Exercise 2: Unified national thread note components
Exercise 3: Unified national thread note
Exercise 4: Metric thread note components
Exercise 5: Metric thread tables
Exercise 6: Fastener tables and clearance holes
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5. Threads and Fasteners
Summary
5

6. Summary
•What will we learn in this topic?
–How to represent threads on an engineering
drawing.
–How to calculate bolt and screw clearance holes.
•Key points
–Threads are represented by thread symbols, not
by a realistic drawing.
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7. Threads and Fasteners
1) Fasteners
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8. Fasteners
•Fasteners include:
–bolts and nuts (threaded)
–set screws (threaded)
–washers
–keys
–Pins
•Fasteners are not a permanent means of
assembly such as welding or adhesives.
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9. Fasteners
•Fasteners and threaded features must be
specified on your engineering drawing.
–Threaded features:Threads are specified in a
thread note.
–General Fasteners:Purchasing information must
be given to allow the fastener to be ordered
correctly.
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10. Threads and Fasteners
2) Screw Thread Definitions
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11. Thread Definitions
•Screw Thread:A ridge of uniform section in
the form of a helix.
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12. Thread Definitions
•External Thread:External threads are on the
outside of a member.
–A chamfer on the end of the screw thread makes
it easier to engage the nut.
Chamfer
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13. Thread Definitions
•External Thread:
–An external thread is cut using a die or a lathe.
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14. Thread Definitions
•Internal Thread:Internal threads are on the
inside of a member.
–An internal thread is cut using a tap.
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15. Thread Definitions
•Major DIA (D):The largest diameter (For both
internal and external threads).
•Minor DIA (d):The smallest diameter.
•Depth of thread:(D-d)/2
•Pitch DIA (d
P):The diameter at which a line cuts
the spaces and threads equally.
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16. Exercise 1
Screw thread features
16

17. Identify the Major,Minor & Pitch
diameters and the Thread Depth.
87
1
2
3
4
5
6
10
9
8
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18. 8
Identify the Major,Minor & Pitch
diameters and the Thread Depth.
1
2
3
4
Minord
10
9
Thread Depth
MajorDdp
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19. Thread Definitions
•Crest:The top surface.
•Root:The bottom Surface.
•Side:The surface between the crest and root.
19

20. Identify the Crest, Rootand Side.
1
2
3
4
10
9
Minord
Thread Depth
dp
20
MajorD

21. Identify the Crest, Rootand Side.
1
2
Crest
Root
10
Side
Minord
Thread Depth
dp
21
MajorD

22. Thread Definitions
•Pitch (P):The distance from a point on a screw
thread to a corresponding point on the next
thread (in/Threads).
•Angle of Thread (A):The angle between the
threads.
22

23. Thread Definitions
•ScrewAxis:Thelongitudinalcenterline.
•Lead:The distance a screw thread advances
axially in one turn.
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24. Identify the Pitch, Screw Axisand Thread Angle.
1
2
10
Crest
Root
Side
Minord
Thread Depth
dp
24
MajorD

25. Identify the Pitch, Screw Axisand Thread Angle.
Axis
Pitch
Angle
Crest
Root
Side
Minord
Thread Depth
dp
25
MajorD

26. Thread Definitions
•Right Handed Thread:Advances when turned
CW. (Threads are assumed RH unless specified
otherwise.)
•Left Handed Thread:Advances when turned
CCW.
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27. Application Question 1
•Name an example of a left handed thread.
Left peddle of a bike
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28. Threads and Fasteners
3) Types of Thread
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29. Types of Thread
•There are many different types of thread
forms (shape) available. The most common
are;
–Unified
–Metric
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30. Types of Thread
•Thread form choice depends on;
–what it will be used for
–length of engagement
–load
–etc…
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31. Types of Thread (Form)
Thread NameFigure Uses
Unified screw
thread
General use.
ISO metric
screw thread
General use.
Square Ideal thread
for power
transmission.
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32. Types of Thread (Form)
Thread NameFigure Uses
ACME Stronger than
square thread.
Buttress Designed to
handle heavy
forces in one
direction.
(Truck jack)
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33. Threads and Fasteners
4) Manufacturing Screw Threads
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34. Manufacturing Threads
•Internal Threads
–First a tap drill hole is cut with a twist drill.
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35. Manufacturing Threads
•Internal Threads
–Then the threads are cut using a tap.
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36. Manufacturing Threads
•Internal Threads
–Chamfers are sometimes cut to allow for easy
engagement.
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37. Manufacturing Threads
•External Threads
–You start with a shaft the same size as the major
diameter.
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38. Manufacturing Threads
•External Threads
–The threads are then cut using a die or on a lathe.
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