threads
TRANSCRIPT
Threads and Fasteners
Fastening – What is it?
• A method of connecting or joining two or more parts together, using devices or processes.
• Examples: Bridges, towers, buildings, transportation, piping, sports, etc.
Threaded Fasteners• A mechanical fasteners used to join
together two or more parts.
• Are formed by using a tapping tool for internal threads, a die for external threads, or a machine tool for either internal or external threads.
Applications
• There are 3 major types of Threaded Fastener Applications, they are:
– Joining
– Adjusting
– Power Transmission
Adjusting• The process of locating or modifying
the position of a part.
• Examples: Drafting Compass – uses a threaded rod to adjust the radial setting.
• Calipers, micrometers, hand wrenches, etc.
Power Transmission• The process of converting or transmitting
the force exerted in one direction to force exerted in the same or a different direction.
• Screw Jacks and certain types of gears use screw threads to transmit power.
• Good example of this is a Car lift
External (male)thread
Internal (female)thread
THREAD TERMINOLOGY
A thread cut on the outside of
a cylindrical body.
A thread cut on the inside of
a cylindrical body.
Internal thread
External thread
Right-handthread
Thread that will assemble when
turned clockwise.
Left-handthread
Thread that will assemble when
turned counter-clockwise.
THREAD TERMINOLOGY
Turnbuckle use RH and LH thread at each end to double displacement.
Crest
Root
Thread angle
THREAD TERMINOLOGY
The peak edge of a thread.
The bottom of the thread cut intoa cylindrical body.
The angle between threads faces.
Internal ThreadExternal Thread
CrestRoot
Thread angle
CrestRoot
Major diameterThe largest diameter on
an internal or external thread.
Minor diameterThe smallest diameter on
an internal or external thread.
Internal ThreadExternal ThreadM
inor
dia
.
Ma
jor
dia
.
THREAD TERMINOLOGY
Min
or d
ia.
Ma
jor
dia
.
Form is the profile shape of thethread.
Thread Form
THREAD TERMINOLOGY
Example :
“knuckle thread form”
COMPARISON OF THREAD CUTTING
External Thread Internal Thread
Major Dia.
Minor Dia.
EXTERNAL THREAD CUTTING
Tools Operation
Threading Die
Die stock
Tools
Tap
Tap wrench
Operation
INTERNAL THREAD CUTTING
Pitch
DEFINITION OF SCREW THREAD TERMS
• The pitch of a thread is the distance from one point on the thread form to the corresponding point of the next thread. Pitch is measured parallel to the thread's axis or centerline. Click to see a sample appear to the right
Pitch
Notice the pitch can be measured
from crest-to-crest OR
Root-to-Root
PitchThe distance between crests of
threads.
Lead The distance a screw will advance
when turned 360o.
THREAD TERMINOLOGY
Internal ThreadExternal Thread
PitchPitch
DEFINITION OF SCREW THREAD TERMS
• The lead (pronounced "leed") is the distance that a threaded part (such as a nut) would move or travel in the horizontal direction if the screw thread was rotated 360 degrees.
• Threads are always assumed to be right handed threads unless marked with the initials LH (Left Hand) at the end of the thread note.
SINGLE AND MULTIPLE THREADS
• Most screws have single threads. Assume single thread unless otherwise noted. Multiple threads are used where parts must screw together or apart quickly. For example, the compass adjustment bar and toothpaste tube caps have multiple threads. Notice in the picture above that:
– Single Thread - The lead is equal to the pitch. – Double Thread - The lead is twice the pitch – Triple Thread - The lead is three times the pitch.
Single and multiple threadsA single thread has a
single ridge in the form of a helix.
A double thread has two ridges started 180 apart.
A triple thread has three ridges, started 120 apart.
The Studio Dog
THREAD SERIES
• Screws of the same diameter are made with different pitches (number of threads per inch) for different uses. The various combinations of diameter and pitch have been grouped into screw-thread series.
• Coarse-thread Series (UNC or NC) In this series the pitch for each diameter is relatively large.
• Fine-thread Series (UNF or NF) In this series, the pitch for each diameter is smaller (there are more threads per inch) than in the coarse- thread series. Example automobiles
• Extra-fine-thread Series (UNEF or NEF) In this series, the pitch is even smaller than in the fine-thread series. Example airplanes and gears
CLASSES OF FITS
• Screw threads are also divided into screw thread classes based on their tolerances (amount of size different from exact size) and allowances (how loosely or tightly they fit their mating parts). You can get exactly the screw thread you need by choosing both a series and a class. In brief, the classes for Unified threads are:
• Class 1 has a large allowance (loose fit). They are used on parts that must be put together or taken apart quickly and easily.
• Class 2 is the thread standards most used for general purposes, such as for bolts, screws, nuts, and similar threaded items.
• Class 3 has stricter standards for fit and tolerance than the others. They are used where thread size must be more exact. Simply, a tighter fitting thread.
“A” Or “B”
• The letter “A” following the fit class number (1,2, or 3) denotes external threads only;
• the letter “B” following the fit class number denotes internal threads only.
READING A THREAD NOTE
Thread Note Definition of Meaning
.750 0.750 diameter (3/4”)
10 10 threads per inch
UNC Unified National Coarse thread series
2 Class 2 (Normal Fit)
A External Thread
READING A THREAD NOTE
• You specify (call for) a particular screw thread by telling its diameter (nominal or major diameter), number of threads per inch, length of thread, initial letters of the series, and class of fit. Any thread you specify will be assumed to be both single and right hand unless you say otherwise. If you mean the thread to be left hand, include the letters “LH” after the class symbol. If you mean it to be double or triple, include "double" or "triple." Some examples using fractional sizes follow:
• 1 1/4-7UNC-1A
Means 1 ¼” diameter, 7 threads per inch, Unified National Course threads, class 1 fit, external threads.
• 7/8-14UNF-2B
Means 7/8” diameter, 14 threads per inch, Unified National Fine threads, class 2 fit, internal threads
1. 1. DetailedDetailed representation representation
2. 2. SchematicSchematic representation representation
3. 3. Simplified Simplified representationrepresentation
THREAD REPRESENTATION
External thread Internal thread
DETAILED REPRESENTATION
60oPitch
Use slanting lines to represent crest and root.
Roots and crest are drawn in sharp Vs.
Thread runout
SCHEMATIC REPRESENTATION
External thread
Pitch Crest (thin line)
Root (thick line)
Use alternate long and short lines for representing
crests and roots of the thread, respectively.
Internal thread
BOLT : Terminology
Bolt is a threaded cylinder with a head.
Hexagonal head
bolt and nutHead
thickness
Thread length
Length
Width across flat
Bolt measurements
Drawboltaxis
Draw anend view
of the head
B
Startingposition
H
Draw abolt head
B/2 B/2
30o
Length
Thread Length
Maj
or
Draw body of a bolt
BOLT : Drawing steps
NUT : Drawing steps
Draw an end viewof the nut
BH
B/2 B/2
Dash lines represent
a threaded hole are
omitted for clarity.
Schematic thread representation
• Staggered lines perpendicular to the axis of the thread represent the thread root and crests.
• Spacing between root and crest lines is any convenient size.
• Root lines are any convenient length.
Drawing detailed representation of V threads• Step 1
• 1. Establish the pitch and half-pitch at the major diameter.
2. Measure intervals the size of the pitch along the major diameter from the first two marks.
3. Add crest lines.
Drawing detailed representation of V threads
• Step 2• 1. Add the V profile for one thread, top
and bottom, locating the root diameter. 2. Add construction lines for the root
diameter.
Drawing detailed representation of V threads• Step 3
• 1. Add one side of the remaining Vs (thread profile).
2. Add the other side of the Vs, completing the thread profile.
Fasteners Quiz
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