420_Topic4_non_prm_joints

420_Topic4_non_prm_joints - Screws, Fasteners, and the...

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MECH 420 Nonpermanent Fasteners Slide 1 Screws, Fasteners, and the design of nonpermanent joints
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MECH 420 Nonpermanent Fasteners Slide 2 Terminology Pitch : distance between adjacent threads. Major diameter ( d ): the largest diameter of the screw thread. Minor diameter ( d r , d 1 ): the smallest diameter of the screw thread. The lead ( l ): the distance the nut moves // to the screw, when it rotates one turn.
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MECH 420 Nonpermanent Fasteners Slide 3 Different threads
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MECH 420 Nonpermanent Fasteners Slide 4 Terminology Pitch diameter : also called the effective diameter is the diameter of an imaginary cylinder whose surface would pass through the thread profiles at such points as to make the width of the groove equal to one-half the basic pitch. • On a perfect thread, this occurs at the point where the widths of thread and groove are equal.
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MECH 420 Nonpermanent Fasteners Slide 5 Screw standard: American National (Unified) • 60 o thread angle with flat or rounded crests. • The metric M & MJ profiles.
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MECH 420 Nonpermanent Fasteners Slide 6 External and internal threads Internal thread (female) External thread (male)
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MECH 420 Nonpermanent Fasteners Slide 7 Threads
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MECH 420 Nonpermanent Fasteners Slide 8 The MJ profile • Rounded fillet at the root of the external thread. • Larger minor diameter for both internal & external threads. • Useful in high fatigue strength scenarios.
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MECH 420 Nonpermanent Fasteners Slide 9 UN, UNRF, UNJF UN UNRF UNJF % thread height engagement 75% to 88% 83% 75% Root Radius NA (Truncated Root) .114 x pitch .180 x pitch http://www.bonaero.com/Glossary.htm
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MECH 420 Nonpermanent Fasteners Slide 10 Using Tables (metric) Specified by writing the diameter and pitch in millimeters: e.g. M12x1.75
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MECH 540 Nonpermanent Fasteners Slide 11 Using Tables (Unified) Specified by writing the nominal major diameter , the number of threads per inch , and the thread series : e.g., 5/8 in-18 UNRF
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