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TE 136 Technical Drafting Chapter 10: Fasteners

TE 136 ? Technical Drafting Chapter 10: Fasteners. Objectives:Identify and describe types of fasteners.Define common screw thread terms.Specify threads and fasteners on a technical drawing.Draw detailed schematic, and simplified thread representations.Name and describe common thread series.Des

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TE 136 Technical Drafting Chapter 10: Fasteners

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    1. TE 136 – Technical Drafting Chapter 10: Fasteners

    2. TE 136 – Technical Drafting Chapter 10: Fasteners Objectives: Identify and describe types of fasteners. Define common screw thread terms. Specify threads and fasteners on a technical drawing. Draw detailed schematic, and simplified thread representations. Name and describe common thread series. Describe and specify classes of thread fits. Draw various types of threaded fasteners.

    3. TE 136 – Technical Drafting Chapter 10: Fasteners A fastener is any kind of device or method for holding parts together. These include: SCREWS NUTS RIVETS BOLTS WELDING BRAZING SOLDERING ADHESIVES COLLARS CLUTCHES KEYS

    4. TE 136 – Technical Drafting Chapter 10: Fasteners Screw . Threaded fastener designed to be inserted through a hole in one member and into a threaded hole in a mating member. Bolt. Threaded fastener designed to pass through holes in mating members and to be secured by tightening a nut from the end opposite the head of the bolt.

    5. TE 136 – Technical Drafting Chapter 10: Fasteners

    6. TE 136 – Technical Drafting Chapter 10: Fasteners

    7. TE 136 – Technical Drafting Chapter 10: Fasteners

    8. TE 136 – Technical Drafting Chapter 10: Fasteners

    9. TE 136 – Technical Drafting Chapter 10: Fasteners

    10. TE 136 – Technical Drafting Chapter 10: Fasteners Screws and screw threads. This principle has been used do long, it is unsure as to whom is responsible for the invention. Archimedes (287-212 B.C.) a Greek mathematician put a screw thread to practical use. With it, he invented a means to raise water from a well (Screw pump). Screws and fasteners have so many uses, it is essential that all drafters, engineers and mechanical designers understand and can draw the different forms.

    11. TE 136 – Technical Drafting Chapter 10: Fasteners The true shape of a screw thread. Screw thread can be a helical ridge on the external or internal surface of a cylinder. It can also be a conical spiral on the external or internal surface of a cone or frustum of a cone. All are basically shaped like a helix (spiral – or helical curve). Right Angle wrapped around a cylinder. Screw thread standards. Practice of interchangeable parts in manufacturing lead to the standardization of screws, threads and fasteners. 1864, William Sellers presented the system to the Franklin Institute in Philadelphia.

    12. TE 136 – Technical Drafting Chapter 10: Fasteners England had established their standards in 1861. In 1948, Canada, Great Britain and the US agreed on a Unified Thread Standards. Globalization of Industrial Manufacturing actually started in the 40’s…Why????? WWII ANSI now keeps the standards along with the Federal Screw Thread Specifications. Why was this federally supported? Finally in 1968 the International Standards Organization adopted the ANSI (Federal) Unified system and made the standards universal. ANSI was forced at this time to apply metric conversions, as Canada and Europe largely use metric components.

    13. TE 136 – Technical Drafting Chapter 10: Fasteners SCREW THREAD TERMS Various Screw Thread Profiles (draw): American National Unified Sharp V Square B & S Worm Thread ACME Knuckle

    14. TE 136 – Technical Drafting Chapter 10: Fasteners Dardelet British Standard Buttress

    15. TE 136 – Technical Drafting Chapter 10: Fasteners Single Thread: a single ridge in the form of a helix. Double Thread: two helical ridges side by side. Triple Thread: three ridges side by side. Right and Left-Hand Threads: Right handed screws in when it is turned clockwise. Left handed screws in when it is turned counterclockwise.

    16. TE 136 – Technical Drafting Chapter 10: Fasteners Unified System There are several constant-pitch-thread (UN) series. 4, 6, 8, 12, 16, 20, 28 or 32 threads per inch. These offer a variety of pitch-diameter combinations that can be used where the coarse, fine, and extra-fine series are not suitable. ANSI Although this system has largely been replaced by the Unified System it is important to note that the symbols are NC, NF, NEF, 8N, 12N and 16N.

    17. TE 136 – Technical Drafting Chapter 10: Fasteners THREAD SERIES: Screws of the same diameter are made with different pitches (numbers of threads per inch) for different uses. In the Unified screw-thread system, the various combinations of diameter and pitch have been grouped in screw-thread series. COARSE THREAD SERIES (UNC OR NC): In this series, the pitch for each diamter is relatively large. This series is for engineering in general. FINE THREAD SERIES (UNF or NF): In this series the pitch for each diameter is smaller (there are more threads per inch) than in the coarse-thread series. Automobile and aerospace industries. EXTRA-FINE THREAD SERIES: (EUNF OR NEF): In this series, the pitch is even smaller than the fine thread series.Used where thread depth needs to be very shallow…aircraft parts and thin-walled tubes.

    18. TE 136 – Technical Drafting Chapter 10: Fasteners Constant Pitch Thread Series: They offer a variety of pitch-diameter combinations that can be used where the three standard series do not offer viable options. Constant-pitch threads are often used as a continuation of coarse, fine and extra fine. When selecting a constant pitch series it is generally practiced to select an 8-, 12 or 16- thread series. EIGHT THREAD SERIES: This series uses 8 threads per inch for all diameters. TWELVE THREAD SERIES: This series uses 12 threads per inch for all diameters. SIXTEEN THREAD SERIES: This series uses 16 threads per inch for all diameters.

    19. TE 136 – Technical Drafting Chapter 10: Fasteners SPECIAL THREADS (UNS, UN OR NS): These are non standard, or special, combinations of diameter and pitch. LETTER SYMBOLS: NC – COARSE THREAD SERIES NF – FINE THREAD SERIES NEF – EXTRA FINE SERIES 8N – EIGHT THREAD SERIES 12N – TWELVE THREAD SERIES 16N – SIXTEEN THREAD SERIES Please Note: The symbol NS denotes special threads in the American National Standards thread series.

    20. TE 136 – Technical Drafting Chapter 10: Fasteners CLASSES OF FITS Screw threads are also divided into screw-thread classes based on tolerances (amount of play from actual size) and allowances (how loosely or tightly they fit their mating parts.) The exact screw thread needed can be obtained by choosing both a series and a class. In brief, the classes for Unified threads are Classes 1A, 2A, and 3A for external threads only and Classes 1B, 2B, and 3B for internal threads only.

    21. TE 136 – Technical Drafting Chapter 10: Fasteners CLASSES 1A and 1B: Large allowance (loose fit). CLASSES 2A and 2B: threads standards used for general purposes (bolts, nuts, screws, and similar threaded items. CLASSES 3A and 3B: these are stricter standards for fit and tolerance than the others. These are used where thread size must be more exact. ANSI also names two other classes: Classes 2 & 3. See appendix 1 of ANSI B1.1 (page

    22. Thread Specifications: A screw thread is specified by giving its nominal (major) diameter, number of threads per inch, length of thread, initial letters of the series, class of fit, and external (A) or internal (B). TE 136 – Technical Drafting Chapter 10: Fasteners

    23. TE 136 – Technical Drafting Chapter 10: Fasteners EXAMPLES: 1.25-7UNC-1A 1.25-INCH DIAMETER, 7 THREADS PER INCH, Unified threads, coarse threads, Class 1, External .75-10UNC-2A (.75-INCH DIAMETER, 10 THREADS PER INCH, Unified threads, coarse threads, Class 2, external

    24. Metric Threads: Specify an ISO metric screw thread by giving its nominal size (basic major diameter) and pitch, both expressed in millimeters. TE 136 – Technical Drafting Chapter 10: Fasteners

    25. Designate a 10mm diameter, 1.25 pitch, fine-thread series as M10 x 1.25. Specify a 10-mm diameter, 1.5 pitch, coarse -thread series, however as M10…for a coarse thread you do not give the pitch unless you also give the length of the thread (M10x1.5x.25) TE 136 – Technical Drafting Chapter 10: Fasteners

    26. TE 136 – Technical Drafting Chapter 10: Fasteners EXAMPLES: 1.25-7UNC-1A 1.25-INCH DIAMETER, 7 THREADS PER INCH, Unified threads, coarse threads, Class 1, External .75-10UNC-2A (.75-INCH DIAMETER, 10 THREADS PER INCH, Unified threads, coarse threads, Class 2, external

    27. TE 136 – Technical Drafting Chapter 10: Fasteners PRO DESKTOP LET’S TRY THIS AGAIN! DETAILED REPRESENTATION Approximates the real look of threads. For this drawing it is not necessary to draw the pitch exactly to scale.

    28. TE 136 – Technical Drafting Chapter 10: Fasteners AUTOCAD Schematic Representation Shows the threads using symbols, rather than as they really look. For this kind of drawing leave out the V’s. Lay off the outside diameter of the screw threads. Lay off the thread depth and chamfer. Draw thin crest lines at right angles to the axis. Draw thick root lines parallel to the crest lines. 1-10 UNC-2A

    29. TE 136 – Technical Drafting Chapter 10: Fasteners AUTOCAD Simplified Representation Much like a schematic representation in that it shows the threads using symbols, rather than as they really look. However, we draw the crest and root lines as hidden lines except whether either may be a visible line. For this kind of drawing leave out the V’s. Lay off the outside diameter of the screw. Lay off the thread depth and chamfer. Draw the chamfer and a line to show the length of the thread. Draw dashed lines for the threads. AUTOCAD SIMPLIFIED

    30. TE 136 – Technical Drafting Chapter 10: Fasteners Other Types of Threaded Fasteners HEXAGON Boltheads and Nuts (fig. 10-32) Lock Nuts and Lock Washers Split Lock Internal Tooth External Tooth Internal-external Tooth Countersunk Tooth Cap Screws: fastens two parts together by passing through a clearance hone in one and screwing into a tapped hole in the other. Machine Screws are used where the fastener must have a smaller diameter.

    31. TE 136 – Technical Drafting Chapter 10: Fasteners Setscrews: used to hold two parts together in a desired position. They do so by screwing through a threaded hole in one part and bearing (pushing) against the other. Woodscrews: made of steel, brass, or aluminum. Roundhead are set with the head above the wood. Flat head are set flush. Specify them by number, length, style of head, and finish. Miscellaneous Threaded Fasteners: Screw hooks, eye hooks, lag screws, etc. are designated by diameter and overall length.

    32. TE 136 – Technical Drafting Chapter 10: Fasteners NON THREADED FASTENERS Keys:used to secure pulleys, gears, cranks and similar parts to a shaft. Rivets: rivets and rods of metal with a preformed head on one end. They are used to fasten sheet-metal plates, structural steel shapes, boilers, tanks, and many other items permanently.

    33. TE 136 – Technical Drafting Chapter 10: Fasteners Assignment: 1.25-10UNC-2A, 2/5 Inches high, Button Head. You will draw: DETAILED DRAWING on PRO/DESKTOP. Provide a Drawing and Split Screen printed on the lexmark. Drawing must be on Layout A. See example. (50 points) SCHEMATIC DRAWING: Using AutoCAD, Layout A, see example. (25 points) SIMPLIFIED DRAWING: Using AutoCAD, Layout A, see example. (25 points) These assignments are due Monday 04/21. Advice…do AutoCAD 1st. You can work on Pro/Desktop at HOME!!! Note: If you do not follow instructions and print the final products as required, ZERO points will be awarded for this drawing.

    34. TE 136 – Technical Drafting Chapter 10: Fasteners References: Mechanical Drawing: CAD-Communications, French, Svensen, Helsel & Urbanick. 12th Edition, MgGraw-Hill, NY University of Tennessee at Martin, Lecture 28, Engineering 478, School of Engineering

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