EML 2023 – Threads and Fasteners

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