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ME180_Lecture_13_Fasteners - Fasteners 1 Mechanical...

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Unformatted text preview: Fasteners 1 Mechanical Fasteners Bolts Cap screws Machine screws Set screws Wood screws Rivets Keys Taper pins Cotter pins 2 Screw Thread Purposes Hold parts together Adjust parts with reference to each other Transmit power 3 Screw Threads Archimedes 3rd century BC Europe 15th century Leonardo da Vinci sketches German watches 16th century Besson French inventor 1569 screw-cutting lathe Industrial Revolution 18th century nuts & bolts Sir Joseph Whitworth 1841 standard thread 1935 American Standard thread 4 Screw-Thread Nomenclature 5 Screw Thread Forms American National Unified standard in US, Can & GB 1948 Metric Square Acme Whitworth Knuckle Buttress Standard Worm 6 Screw-Thread Forms 7 Thread Nomenclature Thread Pitch Distance parallel to the axis between corresponding points on adjacent threads Inch measurement: 1 divided by the number of threads per inch Metric measurement: Measured in millimeters 8 Threads on Drawings Internal & External Detailed Threads Simplified Symbols Schematics Symbols 9 Threads on Drawings 10 Threads on Drawings 11 Threads on Drawings Thread Types Right-Hand Threads Left-Hand Threads Thread series Course Threads Fine Threads Extra Fine Threads Class of Fit (tolerance) 12 Screw-Thread Directions 13 Thread Notes 14 Thread Notes 15 Types of Fasteners Bolt Usually, a through bolt Head on one end Threaded to receive a nut on the other Cap Screw Similar to a bolt Generally, has a greater length of thread Stud Rod threaded on both ends Screwed into one part & held on other with a nut 16 Types of Fasteners 17 Types of Bolts 18 Standard Cap Screws 19 20 21 22 Standard Set Screws 23 Standard Wood Screws 24 Miscellaneous Bolts & Screws 25 Square & Flat Keys 26 Woodruff Keys & Key-Slot Cutter 27 28 Fastening Parts with Cap Screws 29 Cap Screw Assembly What do we need to know? Cap screw diameter Cap screw length Clearance hole diameter Tap drill size Tap drill depth Screw tap specification Screw tap depth 30 Cap Screw Diameter Determined by engineering calculations using materials, thicknesses, loads, etc. You will learn this in other courses, i.e. ME222, ME471, etc. Will be given for example & exam problems 31 Cap Screw Length Determined by thickness of part to be held & function of screw diameter & base material Then, compared to generally available screw lengths based on diameter 32 Cap Screw Drill & Tap Depths 33 Cap Screw Length Length (L) = part thickness (t) + entrance length (A) Where A is a function of the tapped material Determine screw length prior to tap drill depth and thread depth Must check for screw length availability 34 Threads on Drawings 35 Clearance Hole Diameter Determined from screw diameter D + 1/32" for screws up to 1/2" D + 1/16" for screws up to 2" D + 1/8" for screws over 2" 36 Tap Drill Size (Diameter) Use standard tables for nominal screw diameter and thread form & series 37 38 39 40 Tap Drill Depth Calculated based on screw diameter & part material Tap Drill Depth (F) = actual entrance length (A') + thread clearance (B) + unthreaded portion (E) where actual entrance length (A') =screw length (L) part thickness (t) 41 Tap Depth Calculated from screw diameter & part material Thread Depth (C) = actual entrance length (A') + thread clearance (B) where actual entrance length (A') = screw length (L) part thickness (t) 42 Tap Drill Depth 43 Cap Screw Calculation Example A 0.46" thick brass plate is to be fastened to a steel frame with a " unified course thread Class 3 hex head cap screw. What is the diameter of the hole drilled through the brass plate? What are the specifications for the hole drilled into the steel frame? What are the specifications for the tapped hole? What are the specifications for the fastener? 44 Cap Screw Length L=t+A t = 0.46" A = D (steel) = 0.75" Therefore, minimum screw length = 1.21" Check of screw length increments indicates using 1.25" long screw A' = L t = 1.25" 0.46" = 0.79" 45 Clearance Hole Diameter D + 1/16" for screws up to 2" Therefore, clearance hole diameter = 3/4" + 1/16" = 13/16" 46 Tap Drill Size (Diameter) From the standard tables, use 21/32" drill 47 Depth of the Tap Drill F = A' + B + E = 0.79" + 4/10" + 4/10" = 1.59" 48 Thread Depth C = A' + B = 0.79" + 4/N = 0.79" + 4/10" = 1.19" 49 Drawing Notes Clearance hole: 13/16 DRILL Tap drill: 21/32 DRILL, 1.59 DEEP Tap: 3/4 10UNC 3B x 1.19 DEEP Fastener: 3/4 10UNC 3A x 1 1/4 HEX HEAD CAP SCREW 50 ...
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