Screw Threads Copyright © Texas Education Agency, 2014. All rights reserved. Screw Thread Uses Fasteners Adjusters Transfer Power Mechanical Advantage Copyright © Texas Education Agency, 2014. All rights reserved. Screw Thread Uses • 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 Copyright © Texas Education Agency, 2014. All rights reserved. Simple Definition of a Thread A screw thread is a wedge wrapped around a cylinder. Copyright © Texas Education Agency, 2014. All rights reserved. Coarse Thread Metric Square Thread Copyright © Texas Education Agency, 2014. All rights reserved. External and Internal Threads External Threads are on a bolt. Internal Threads are in a nut. Copyright © Texas Education Agency, 2014. All rights reserved. Right-Handed Bolt • All bolts and nuts are right handed unless marked. • Right-handed threads tighten by turning clockwise. • Left-handed threads tighten by turning counter-clockwise. Copyright © Texas Education Agency, 2014. All rights reserved. Thread Size Threads are sized by the diameter of the bolt and the number of threads per inch. Copyright © Texas Education Agency, 2014. All rights reserved. Threads per Inch 1 2 3 4 5 6 7 8 9 10 A ¾” – 10 bolt has 10 threads per inch. Copyright © Texas Education Agency, 2014. All rights reserved. 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 Copyright © Texas Education Agency, 2014. All rights reserved. Metric Threads • 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). Copyright © Texas Education Agency, 2014. All rights reserved. Standard Metric Sizes Coarse Threads M6.3 X 1 M8 X 1.25 M10 X 1.50 M12 X 1.75 M14 X 2 M16 X 2 M20 X 2.5 Fine Threads M6.3 X 0.75 M8 X 1 M10 X 0.75 M12 X 1 M14 X 1.5 M16 X 1.5 M20 X 1 Copyright © Texas Education Agency, 2014. All rights reserved. Types of Threads Standard threads are V-style with 60° angles. Copyright © Texas Education Agency, 2014. All rights reserved. Types of Threads Square Threads are square in shape, with the same width and depth. Copyright © Texas Education Agency, 2014. All rights reserved. Types of Threads ACME Threads are like square threads, but with a 29° angle on the sides; they’re used to transfer power. Copyright © Texas Education Agency, 2014. All rights reserved. Types of Threads Pipe Threads are tapered; the back is shallower than the front of the thread. Copyright © Texas Education Agency, 2014. All rights reserved. Basic Thread Terminology • • • • • A. Major Diameter B. Pitch Diameter C. Minor Diameter D. Crest E. Root Copyright © Texas Education Agency, 2014. All rights reserved. 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. Copyright © Texas Education Agency, 2014. All rights reserved. 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 Copyright © Texas Education Agency, 2014. All rights reserved. Basic Thread Terminology Copyright © Texas Education Agency, 2014. All rights reserved. Basic Thread Terminology • 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. Copyright © Texas Education Agency, 2014. All rights reserved. Assessment • Quiz • Cut 10 different sizes of internal and external screw threads using a set of tap and die, or lathe and tap. Copyright © Texas Education Agency, 2014. All rights reserved. Reference • 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 Copyright © Texas Education Agency, 2014. All rights reserved.