screw threads copyright © texas education agency, 2014. all rights reserved
TRANSCRIPT
Screw Threads
Copyright © Texas Education Agency, 2014. All rights reserved.
Screw Thread Uses
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Fasteners
AdjustersTransfer Power
Mechanical Advantage
Screw Thread Uses
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• Fastener – (bolts, nuts, and screws) used to hold parts together
• Movement – (lathe lead screw) transmits twisting power to straight line motion
• Mechanical advantage – (vise and clamp screws) increases force to hold items
• Adjustments – allows parts to be moved
Simple Definition of a Thread
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A screw thread is a wedge wrapped around a cylinder.
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Right Hand
Left Hand
Metric Square Thread
ACME Thread
Coarse Thread
Pipe Thread
External
Fine Thread
Internal
External and Internal Threads
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External Threads are on a bolt.
Internal Threadsare in a nut.
Right-Handed Bolt
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• All bolts and nuts are right handed unless marked.
• Right-handed threads tighten by turning clockwise.
• Left-handed threads tighten by turning counter-clockwise.
Thread Size
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Threads are sized by the diameter of the bolt and the number of threads per inch.
Threads per Inch
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A ¾” – 10 bolt has 10 threads per inch.
1 2 3 4 5 6 7 8 9 10
Standard Thread Sizes
Coarse Threads• ¼” – 20• ³∕₈” – 16• ⁷∕₁₆” – 14 • ½” – 13 • ⁹∕₁₆” – 12• ⅝” – 11• ¾” – 10
Fine Threads• ¼” – 28• ³∕₈” – 24• ⁷∕₁₆” – 20• ½” – 20• ⁹∕₁₆” – 18• ⅝” – 18• ¾” – 16
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Metric Threads
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• Metric threads are sized by diameter and thread pitch in millimeters.
• The coarse metric threads use only the diameter size (example, M10).
• The fine metric threads will have the diameter and pitch size stated (example, M10 X 1.25).
Standard Metric Sizes
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Coarse ThreadsM6.3 X 1M8 X 1.25M10 X 1.50M12 X 1.75M14 X 2M16 X 2M20 X 2.5
Fine ThreadsM6.3 X 0.75M8 X 1M10 X 0.75M12 X 1M14 X 1.5M16 X 1.5M20 X 1
Types of Threads
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Standard threads are V-style with 60° angles.
Types of Threads
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Square Threads are square in shape, with the same width and depth.
Types of Threads
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ACME Threads are like square threads, but with a 29° angle on the sides; they’re used to transfer power.
Types of Threads
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Pipe Threads are tapered; the back is shallower than the front of the thread.
Basic Thread Terminology
• A. Major Diameter• B. Pitch Diameter• C. Minor Diameter• D. Crest• E. Root
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Basic Thread Terminology
• A. Major Diameter- the largest diameter of a bolt at the crest, or the diameter of the roots of a nut.
• B. Pitch Diameter- the diameter halfway between the major diameter and minor diameter.
• C. Minor Diameter- the small diameter of a bolt at the root, or the diameter of the crest of a nut.
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Basic Thread Terminology
• D. Crest- the top surface where the two sides of the threads meet.
• E. Root- the bottom surface where the two sides of the threads meet.
Crest
Root
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Basic Thread Terminology
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Basic Thread Terminology
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• Pitch- the distance between thread crests of the thread.
• Height- the measurement from the root of the thread to the crest of the thread.
• Slope- the angle of the side of the thread.
Assessment
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• Quiz• Cut 10 different sizes of internal and external
screw threads using a set of tap and die, or lathe and tap.
Reference
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• Oberg, E. (2012). Machinery’s handbook, 29th. South Norwalk, CT: Industrial Press, Inc.
• Threads and Threading: pages1802-2121• US Standard Screw Thread: page 1806• Definitions: pages 1808-1813• Metric: pages 1878-1920• Acme: pages 1921-1944• Square: page 1944• Pipe: pages 1956-1972