eml 2023 – threads and fasteners
DESCRIPTION
EML 2023 – Threads and Fasteners. Lecture 1 - Nomenclature. Thread Terminology. Thread Callouts - Metric. (mm). (mm). (mm). Thread Callouts – ANSI Unified. 1 – loosest fit 2 – normal fit 3 – most exact fit. B represents internal thread. UNC – Unified National Course - PowerPoint PPT PresentationTRANSCRIPT
EML 2023 – Threads and Fasteners
Lecture 1 - Nomenclature
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Thread Terminology
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Thread Callouts - Metric
(mm)
(mm)
(mm)
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Thread Callouts – ANSI Unified
(in) UNC – Unified National CourseUNF – Unified National FineUNEF – Unified National Extra FineUN – Unified National
1 – loosest fit2 – normal fit3 – most exact fit
B represents internal thread
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Thread Callouts – ANSI Unified
(in)Assumes course threads with a nominal fit (2).
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Goal:• connect the top part to the bottom
part using a #10-24 cap screw which has a head taper of 82˚
• must determine length of screw
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Steps:
• buy the screw
• drill a countersunk hole without threads (clearance hole) into the top part
• drill a threaded hole in the bottom part
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2 things to know
1. if you tap a hole– the thread length should be at least twice the
diameter of the fastener
2. if you use a bolt to connect some bodies– the bolt should extend beyond the nut by at least two
thread pitches
How long should the screw be?
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• the major diameter of the #10 screw is .190”
• the length of the screw must be at least as long as
.30” + 2.19” =.68
• will purchase a #10-24 screw that is .75” long
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The major diameter of the screw is .190”.
What should the diameter of the clearance hole be?
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Was able to download a SolidWorks part file of this cap screw.
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A clearance hole has been created for a #10 flat head screw with an 82˚ head taper.
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• A tapped hole for a #10-24 screw.
• The screw we selected is .75” long. Therefore the thread depth of the hole must be at least .75”-.3” = .45” deep.
• I selected a thread depth of 0.45” and a pilot hole depth of .66”.
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If you only tap the blue body to the recommended depth of 2 major , i.e. .38”,you will have the following.
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2nd Example Problem
3/8” – 24 cap screw
blocks are 1.5”1.5”.50”
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2 things to remember
1. if you tap a hole– the thread length should be at least twice the
diameter of the fastener
2. if you use a bolt to connect some bodies– the bolt should extend beyond the nut by at least two
thread pitches
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Determining Bolt Length
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Bolt length calculation
Bolt must be 1.988” long plus the distance of 2 extra pitches.
The bolt has 24 threads per inch. Two extra pitches will require an extra 1/12” of an inch.
Total minimum length is 1.988+0.083 = 2.071” .
Find the next longest available bolt.
21/64”
.08”
.50”
1.988”
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2 things to remember
1. if you tap a hole– the thread length should be at least twice the diameter of the
hole
2. if you use a bolt to connect some bodies– the bolt should extend beyond the nut by at least two thread
pitches