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Screw Threads

Screw Threads. Introduction. Thread terminology. Thread drawing and dimensioning. Threaded fastener. TOPICS. Introduction. FASTENING TYPE. 1. Permanent. Welding. Gluing. Riveting. key. FASTENING TYPE. 2. Temporary. 2.1 Threaded fastener - bolts - studs

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Screw Threads

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  1. Screw Threads

  2. Introduction Thread terminology Thread drawing and dimensioning Threaded fastener TOPICS

  3. Introduction

  4. FASTENING TYPE 1. Permanent Welding Gluing Riveting

  5. key FASTENING TYPE 2. Temporary 2.1 Threaded fastener - bolts - studs - screws 2.2 Non-threaded fastener - keys - pin

  6. THREAD APPLICATION 1. To hold parts together. 2. To move part(s) relative to others. Part A Part B Part C

  7. THREAD APPLICATION 1. To hold parts together. 2. To move part(s) relative to others. Wood working vise Palm fruit pressing machine

  8. Thread Terminology

  9. THREAD TERMINOLOGY A thread cut on the outsideofa cylindrical body. External (male) thread A thread cut on the insideof a cylindrical body. Internal (female)thread External thread Internal thread

  10. Turnbuckle use RH and LH thread at each end to double displacement. THREAD TERMINOLOGY Thread that will assemble when turned clockwise. Right-handthread Thread that will assemble whenturned counter-clockwise. Left-hand thread

  11. Thread angle Crest Root Crest Root THREAD TERMINOLOGY Crest The peak edge of a thread. The bottom of the thread cut into a cylindrical body. Root Thread angle The angle between threads faces. External Thread Internal Thread

  12. Minor dia. Major dia. Major dia. Minor dia. THREAD TERMINOLOGY The largest diameter on an internal or external thread. Major diameter The smallest diameter on an internal or external thread. Minor diameter External Thread Internal Thread

  13. Pitch Pitch THREAD TERMINOLOGY The distance between crests of threads. Pitch The distance a screw will advance when turned 360o. Lead External Thread Internal Thread

  14. Example : “knuckle thread form” THREAD TERMINOLOGY Form is the profile shape of the thread. Thread Form

  15. Tools Operation EXTERNAL THREAD CUTTING • Threading Die • Die stock

  16. Tools Operation INTERNAL THREAD CUTTING • Twist drill • Tap • Tap wrench

  17. External Thread Internal Thread COMPARISON OF THREAD CUTTING Minor Dia. Major Dia.

  18. Thread Drawing

  19. THREAD REPRESENTATION 1. Detailed representation 2. Schematic representation 3. Simplified representation

  20. Use slanting lines to represent crest and root. Roots and crest are drawn in sharp Vs. Pitch 60o DETAILED REPRESENTATION Internal thread External thread Thread runout

  21. Use alternate long and shortlines for representing crests and roots of the thread, respectively. Root (thick line) Pitch Crest (thin line) SCHEMATIC REPRESENTATION Internal thread External thread

  22. Use thick continuous lines for representing crest and thin continuous lines for representing rootof the thread, respectively. Pitch/2 Root Crest SIMPLIFIED REPRESENTATION External thread Internal thread Thread runout

  23. Use thick continuous lines for representing crest and thin continuous lines for representing rootof the thread, respectively. SIMPLIFIED REPRESENTATION External thread Internal thread Sectional view

  24. P/8 60o P/4 Pitch, P ISO (METRIC) THREAD Internal thread External thread Center of thread assembly Thread assemble occurs if and only if both (internal & external) thread have an equal nominal size (or diameter) and pitch.

  25. METRIC COARSE THREAD [Table 9.1] Metric thread Minor diameter ≈ Tap drill size In thread drawing, the following relationship is used. Minor diameter = Major diameter – Pitch

  26. METRIC FINE THREAD [Table 9.2] Minor diameter ≈ Tap drill size In thread drawing, the following relationship is used. Minor diameter = Major diameter – Pitch

  27. DRAWING STEPS OF EXTERNAL THREAD Draw an arc that represents a root. Draw 45o Chamfer Draw line making 30o with thread axis Draw a circle that represents a crest. Draw thread axis Major dia. Minor dia. Thread Length Starting position

  28. DRAWING STEPS OF THREADED HOLE Internal Thread 1. Through threaded hole Sectional view Draw a crest Draw a root root crest Draw thread axis Major dia. Minor dia. Draw a circle that represents a crest. Section lines are drawn into the crest of a thread. Draw an arc that represents a root.

  29. DRAWING STEPS OF THREADED HOLE 2. Blinded threaded hole Draw thread axis Major dia. Minor dia. Draw a circle that represents a crest. Thread depth Hole depth Draw an arc that represents a root.

  30. DRAWING STEPS OF THREADED HOLE 2. Blinded threaded hole Sectional view

  31. Uselocal noteto specify :- thread form, nominal size, pitch(if it is a fine thread) Usetypical methodto specify :- thread length. Thread length DIMENSIONING EXTERNAL THREAD M ×1.5 10 Coarse thread ×1.0 Fine thread xx

  32. DIMENSIONING THREADED HOLE Uselocal noteto specify 8.50 Drill, 20 Deep, M10 Tapped, 15 Deep 1. Tap drill size 2. Drill depth 3. Thread form 4. Nominal size 5. Pitch 6. Thread depth

  33. Exercise

  34. Exercise

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