ENGR-22_Lec-20__Fasteners-1_Specs.ppt 1 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Bruce Mayer, PE Registered Electrical & Mechanical Engineer Engineering 22 Threaded Fasteners

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 2 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Skill-Development Goals  Define and Label the Parts of A Screw Thread  Identify Various Screw Thread Forms  Draw Screws in Forms Detailed Schematic Simplified  Properly Apply Screw Thread Technical Specifications

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 3 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Skill-Development Goals cont.  Identify Different Fasteners and Describe Their Use  Draw the Various Types of Screw Heads

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 4 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Skill-Development Goals  State the Two MOST Important Threaded Fastener References for Structural (Mech/Civ/Chem) Design Engineers  Use AutoCAD to QUICKLY Draw Most Threaded Fasteners in Any Size and Any Representation  Invoke the AutoCAD “Design Center” tool to Construct Fastener Representations

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 5 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Threaded Fasteners  Helical Threads Have Three Main Applications 1.Used to HOLD parts together The Classic Application 2.Used to ADJUST the Position of parts with reference to one another The “Screw Adjustment” knob 3.Used to TRANSMIT Power e.g, screw Jack, Worm Gear Drive

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 6 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Screw Thread Terminology  Ref ASME B1.7M-1984 (R2001) Nomenclature Definitions, and Letter Symbols for Screw Threads

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 7 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Common Tread forms Joining Lite-Duty (e.g., Light Bulbs) Pwr Xmission

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 8 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Thread Pitch  USA → Pitch is Inverse of Thread Count  Metric → Pitch in the Thread Designation

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 9 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Unified (USA) Thread Series  The Unified System (UN) Adopted on 18- Nov-1948 by the USA, UK, & Canada Made fasteners Interchangeable  The UN Designation (Spec) has Two Main Elements The Major (outside) Diameter –Specified by Either  A size No. running from 0-12 ( inches)  The Major Dia, in Fractional (ugh!) inches (¼-4 inches) The Inverse Pitch in Threads per Inch

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 10 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics UN Thread Series – 6 Total 1.COARSE Series (UNC or NC) For General Use Where Rapid Assembly is Required –Threads Engage, or “Start” Easily 2.FINE Series (UNF or NF) For Applications Requiring Greater Strength or Where the Length of Engagement is Limited –Used Extensively in Aircraft and Automobile Manufacturing

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 11 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics UN Thread Series – cont 3.EXTRA FINE Series (UNEF or NEF) For Highly Stressed Parts 4.8N Series (8N) A Substitute for Coarse-Thread Series for Diameters larger Than 1” –All diameters have 8 threads per inch. Often Used on bolts for high pressure pipe applications.

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 12 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics UN Thread Series – cont N Series (12 UN or 12N) A Continuation of the Fine-Thread Series for Diameters Larger than 1.5” –All diameters have 12 thds/in. Used in boiler work and in Machine Construction. 6.16N Series (16 UN or 16N) A Continuation of the ExtraFine-Thread Series for Diameters Larger than 2” –All diameters have 16 thds/in. Used on adjusting collars and other applications where thread must have fine adjustment regardless of diameter.

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 13 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Screw Fastener Specification  Defaults That Need NOT be Part of Callout NC or NF implied by Diameter & TPI Class → Default is 2A or 2B Hand → Default is RIGHT

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 14 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics UN Thread Classes  Two Types of Classes A.Refers to EXTERNAL Threads (Bolts & Screws) B.Refers to INTERNAL Threads (Nuts & “Tapped” holes)  Class Descriptions 1.Provide Liberal Allowance for Ease of Assembly Even When Threads are Dirty or Slightly Damaged Not Commonly Used

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 15 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics UN Thread Classes cont  Class Descriptions cont. 2.For Commercially Produced bolts, screws, nuts, and other threaded fasteners By Far the Most Common 3.Used in Precision Assemblies where a Close Fit is Required to WithStand Stress & Vibration Typical Use is Aircraft or other Hi-Vibration Applications

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 16 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Metric Thread Specification  Note That Pitch is Stated Explicitly Compares to Inverse Pitch (TPI) for the Unified Specification

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 17 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Left & Right Hand Treads  Why LH Threads??? To Distinguish a Critical Connection To Make One End of a Turn-Buckle When Needed to Counter Loosening Tendency of Rotating Machinery

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 18 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Detailed Thread Representation  Used when diameter of thread is 1” or larger on plotted or Hand drawing.  Use ONLY When It is Important to Show the Function of the Thread Not Typical for Hand Drawings

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 19 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Simplified & Schematic Forms Best Overall  Imply depth of thread with hidden lines for simplified representation  Use alternating LONG THIN & SHORT THICK lines to represent ROOT & CREST lines in schematic representation Spacing is SCHEMATIC; need not Match Actual Pitch

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 20 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Representation Comparison  Detailed → Very Laborious to Construct Very Infrequently Used on Engineering Drawings  Simplified → Fast but Potentially Confusing Hidden Lines can be Mistaken for Object Features  Schematic → Best Overall Fast To Draw, Clearly ID’s the Threads

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 21 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Threads in Section  Normal Practice is to NOT Section the Fastener

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 22 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Tapped Holes  To Avoid the use of a Thru-Hole & Nut, The “Parent” Material of An object May be Thread “Tapped” That is, Threads are Cut Into the Side of a Hole Drilled into the Base Material  Even Thin parts may tapped By Use of A thru Hole Rule of Thumb for the MINIMUM number of threads = 3 –For Light-Duty applications, can use 1.5

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 23 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Forming Tapped Holes

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 24 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Pipe Threads  Pipe Threads have An INTERFERENCE TAPER that Results in PERMANENT Material DEFOMATION That (Hopefully) Produces a Fluid-Tight Seal at the Joint.

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 25 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Pipe Thread Representations  Taper Should be Shown Need Not be to Scale

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 26 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Pipe Thread Representations  Only ONE TPI Spec for Pipe Threads ASME B = American National Standard Taper Pipe Thread  National Pipe Thread (NPT) for Short Callout Requires Only the “NPT” Notation, Along with the “Size”

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 27 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Bolts, Screws, and Studs  Does Anyone Know the Difference?  A BOLT is Used with A NUT  A SCREW is Used with A TAPPED hole The Hole May be SELF-Tapped –e.g., Wood Screws  A STUD is a TREADED ROD that is Inserted into a TAPPED HOLE to leave Exposed a Threaded STEM A Stud May Also be WELDED to a Surface

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 28 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Machine Screw Head Types  Slot Head Provides More Driving Torque, But Driver is Hard to Center → Not good for Power Driving

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 29 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Threaded Inserts  Use With Soft Parent Materials Such as Aluminum, Wood, Plastic, etc.

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 30 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Insert Advantages  Greater clamping pressure in softer materials - provides higher strength, better seals.  Better user of high-tensile-strength fasteners.  Resistance to vibration in assembly.  High-quality standard threads without tapping.  Permanent, wear-resistant threads.  Protective of expensive castings and moldings.  Reduced performance loss from cold flow of plastic.  Reduce risks in molding cycle.  Easy to install in a drilled or molded hole.  Suitable for automatic installation.  Wide variety of types to fit virtually any application

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 31 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Fastener Design References  If you design with Threaded Fasteners; you MUST get access to These Books IISBN: h

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 32 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Mach-HdBk,23red Ed Page 1325(of 2511)

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 33 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Wheel ReInvention  It has been estimated that CAD-Using Engineers Spend up to 20 Hrs/Month REDRAWING Part for their Designs  Avoid Reinventing the Wheel by Calling Part Maker and asking for CAD file Consult OnLine Parts DataBases Consult your Company’s CAD-Block Library Ask your Colleagues Check AutoCAD Tools

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 34 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Building a Fastener  When I left Watkins- Johnson Co. in 2000 We had 775 items in our CAD Library  Let’s Build a A Bolt from a “Forms” File  The Bolt/Screw Spec 3/8-16 x 1.25 UNC SH Cap Screw

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 35 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics All Done for Today Fasteners Make the World Go Round Molded-In Inserts for Plastic Materials Bolt-Failure by Reversing-Load Mechanical- Fatigue → See ENGR45

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 36 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Bruce Mayer, PE Licensed Electrical & Mechanical Engineer Engr/Math/Physics 25 Appendix 

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 37 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Build-Screw Demo Open File New File using Acad.dwg 2.Make Layer “Bolt” Continuous & GRN 3.Save As _125_shcap.dwg 4.Set Snap to Open Fastener Forms file Threaded_Fastener _Forms_0509.dwg 6.Find SH Cap Form and Copy to ClipBd 7.Paste SHcap Form into new dwg 8.Return to Forms and Copy Detailed Thread Rep 9.Paste detailed Thd- Form into new-dwg 10.Chk Major dia at 1”

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 38 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Build-Screw Demo Scale all by Ratio of 1: Move TopV of Screw Head 13.Rotate Detailed Thd-form by 90° 14.Explode screw Side view 15.Make Xline at base of Scr Hd 16.Offset xline to rt by 1.25 (scr length) 0.5 (unthd’s shank) 17.Erase Simplifed- form lines 18.Stretch shank line to 0.5 xline 19.Make xline on CL of Screw

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 39 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Early Result  Just before trimming out unneeded thds

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 40 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Build-Screw Demo Trim & Erase unused SideV line to Rt of 0.5 xLine 21.Erase Unneeded Thd-details 22.Connect UnThd’s Shank to Thd’d Major Dia. With Fillet 23.Move TopV of Cap Scr to Lt of SideV 24.Delete xLine Detailed Thd-Form 25.Put all objects on Bolt Layer 26.Adjust LtScale to 0.1

ENGR-22_Lec-20__Fasteners-1_Specs.ppt 41 Bruce Mayer, PE Engineering 22 – Engineering Design Graphics Final Result  Caveat: Screw HEAD may NOT be to- Scale for 3/8 Socket Head as we scaled down from the 1” Version If Clearance is an issue, then Chk Hd Diameter and Height against Machinery’s HandBook