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EML 2023 – Threads and Fasteners

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

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EML 2023 – Threads and Fasteners

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  1. EML 2023 – Threads and Fasteners Lecture 1 - Nomenclature

  2. Thread Terminology

  3. Thread Callouts - Metric (mm) (mm) (mm)

  4. Thread Callouts – ANSI Unified 1 – loosest fit 2 – normal fit 3 – most exact fit B represents internal thread UNC – Unified National Course UNF – Unified National Fine UNEF – Unified National Extra Fine UN – Unified National (in)

  5. Thread Callouts – ANSI Unified Assumes course threads with a nominal fit (2). (in)

  6. 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

  7. Steps: • buy the screw • drill a countersunk hole without threads (clearance hole) into the top part • drill a threaded hole in the bottom part

  8. 2 things to know • if you tap a hole • the thread length should be at least twice the diameter of the fastener • 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?

  9. 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

  10. The major diameter of the screw is .190”. What should the diameter of the clearance hole be?

  11. Engineer’s Handbook http://www.engineershandbook.com/

  12. Was able to download a SolidWorks part file of this cap screw.

  13. A clearance hole has been created for a #10 flat head screw with an 82˚ head taper.

  14. 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”.

  15. If you only tap the blue body to the recommended depth of 2 major , i.e. .38”,you will have the following.

  16. 2nd Example Problem 3/8” – 24 cap screw blocks are 1.5”1.5”.50”

  17. 2 things to remember • if you tap a hole • the thread length should be at least twice the diameter of the fastener • if you use a bolt to connect some bodies • the bolt should extend beyond the nut by at least two thread pitches

  18. Determining Bolt Length

  19. 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. .50” 1.988” .08” 21/64”

  20. 2 things to remember • if you tap a hole • the thread length should be at least twice the diameter of the hole • 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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