Threads

1
Threads Fasteners

• Competency D505.00
• Describe various types of thread and fastener
  representations and their annotations.

2
Threads Fasteners

• Objective D505.01
• Specify threads and fasteners on a technical
  drawing.

3
Basic Applications of Threads

• How are threads used?

• Hold parts together
• Adjust parts
• Transmit power

4

• All screw threads wind around a shaft in a curve
  called a HELIX

5
Tapping A Small Hole
Tap Tool - is a small fluted cutting tool with
cutting teeth shaped to form small internal
threads.
6
Cutting Large Threads
External threads are formed by cutting helical
grooves around the shaft on a lathe.
7
Thread Terminology
8
Thread Forms

• Sharp V or Sellers Thread
• First U.S. Standard Thread
• Now used on brass pipe work

9
Thread Form

• Unified Thread
• Adopted by the U.S., British, and Canada after
  World War II as an ANSI standard.
• Mainly used for fastening and adjusting

10
Thread Form

• Metric Thread
• Adopted in 1946 by the International Organization
  for Standardization (ISO)

11
Thread Form

• Square Thread
• Theoretically the ideal thread for power
  transmission
• Tough to cut the threads because of the 90 angles

12
Thread Forms

• ACME Thread
• Modification of the square thread
• Stronger and easier to cut than the square thread
• Also used to transmit power.
• Better know as a worm thread.

13
Thread Forms

• Whitworth Thread
• First standard in England
• Has been replaced by the Unified thread

14
Thread Forms

• Knuckle Thread
• Typically rolled from sheet metal
• Sometimes is formed by casting
• Used in light bulbs, sockets, and jar bottle
  tops

15
Thread Forms

• Buttress Thread
• Designed to transmit power in one direction
• Used on large guns, screw jacks, and Bumper Jacks.

16
Thread Representation
Most Common Practice Of The Two

• Symbolic Method

Is used for all forms of thread forms
17
Thread Representation
INTERNAL THREADS
EXTERNAL THREADS
Detailed Method
Primarily used for threads 1 and larger.
18
Conventional Practices
SIMPLIFIED TECHNIQUES FOR A THROUGH HOLE
19
Conventional Practices SIMPLIFIED SYMBOL
Blind Hole
The tapped hole as it would appear on a drawing
20
Conventional Practices SIMPLIFIED SYMBOL
Blind Hole
A BLIND TAPPED HOLE AS IT WOULD APPEAR ON A
DRAWING IF TAPPED TO THE BOTTOM OF THE HOLE
21
Can You Identify The Following Conventions Within
The Sectional View?

• Major diameter
• Thread Axis
• Minor diameter
• Thread depth

22
Can You Identify The Following Conventions Within
The Elevation View?

• Tapped hole
• Major diameter
• Thread depth
• 30 degrees

23
Annotations For Unified Thread
Major diameter of threads
Number of threads per inch
Unified National
Coarse
Class of Fit
Internal thread
24
Example Of A Screw Thread Table
25
Annotation For Metric Threads
Metric thread
Major diameter
Separation
Thread pitch
M10 X 1.25
26
Example Of A Metric Screw Thread Table
27
Left Hand Threads Advances Counterclockwise
Right Hand Threads Advances Clockwise
28
Other Types Of Threaded Fasteners

• Bolt Nut
• Cap Screws
• Machine Screws
• Set Screws
• Wood Screws

29
CAP SCREWS

• Used to fasten parts together.
• Have a naturally bright finish to match the
  machined part.
• Chamfer to the depth of the first thread

30
Cap Screw Types
(a) Round, (b) Pan, (c) Oval, (d) Hex, (e)
Socket, (f) Flat, and (g) Phillips
31
Standard Dimensions Used In Drawing The Cap Screw
D Diameter of the shaft.
32
Cap Screws Bolts

• What is the difference between a cap screw and a
  bolt?
• Cap screws fasten into a threaded blind hole.
• Bolts are usually accompany by a Nut to fasten
  parts together.

33
Hex Socket Cap Screw
Is BEST used with a counterbored hole
34
Flat Head CapScrew
Countersinking is the BEST type of machined hole
to accept a FLAT HEAD cap screw.
35
Set Screws

• There are generally two types square-head and
  headless.
• Because of safety issues the headless setscrew
  would be best for rotating parts.

36
Set Screw
Used to hold the collar to the shaft
This type of set screw would be a safety issue
if the assembly had a rotating motion.
37
Fasteners For Wood

• Wood Screws create their own thread when you
  drive them into soft woods such as pine and
  spruce.
• Cone shaped shafts for easy entry into the wood.
• Hard woods, such as maple or oak, may require
  drilling a pilot hole.
• Wood screws have flat, round, or oval heads with
  slotted or Phillips head configurations.

38
Wood Screw Head Types

• (a) Round, (b) Flat, (c) Oval, (d) Phillips

39
Non-Threaded Fasteners

• Keys Keyways
• Rivets
• Cotter Pins

40
Keys

• Are used to prevent relative movement between,
  wheels, pulleys, gears, cranks, and similar parts
  to a shaft.

41
Identification
42
Square Key Design is used for heavy-duty
functions. Sometimes referred to as a flat key.
43
Gib Head Key It is exactly the same as the
square key except that it has a gib head, which
provides for easy removal.
44
Pratt Whitney Key is rectangle in shape with
semi-cylindrical ends.
45
Woodruff Key is semicircular in shape and is
often used in machine-tool work. The bottom of
the key fits into a semicircular key slot cut
with a Woodruff cutter and the top into a
rectangular slot.
46
Stock Key Size Based On The Diameter Shaft
47
Types of Pins
Clevis pin
Straight pin
Taper pin
Cotter pin
48
Rivets

• Rivets are regarded as permanent fasteners.
• Generally used to hold sheet metal or rolled
  steel shapes together.
• The shaft of the rivet is inserted into the
  aligned holes of the matting parts and then
  formed to create a head on the opposite end of
  the shaft, establishing a permanent assembly.