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

Engineering 22
Threaded
Fasteners
Bruce Mayer, PE
Registered Electrical & Mechanical Engineer
[email protected]
Engineering 22 – Engineering Design Graphics
1
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
2
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Skill-Development Goals cont.
 Identify Different
Fasteners and
Describe Their
Use
 Draw the Various
Types of Screw
Heads
Engineering 22 – Engineering Design Graphics
3
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
4
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
5
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Screw Thread Terminology
 Ref ASME B1.7M-1984 (R2001)
• Nomenclature Definitions, and Letter
Symbols for Screw Threads
Engineering 22 – Engineering Design Graphics
6
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Common Tread forms
Joining
Joining
Pwr Xmission
Lite-Duty (e.g., Light Bulbs)
Engineering 22 – Engineering Design Graphics
7
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Thread Pitch
 Metric → Pitch in the Thread Designation
 USA → Pitch is Inverse of Thread Count
Engineering 22 – Engineering Design Graphics
8
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Unified (USA) Thread Series
 The Unified System (UN) Adopted on 18Nov-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 (0.06-0.216 inches)
 The Major Dia, in Fractional (ugh!) inches (¼-4 inches)
• The Inverse Pitch in Threads per Inch
Engineering 22 – Engineering Design Graphics
9
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
10
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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.
Engineering 22 – Engineering Design Graphics
11
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
UN Thread Series – cont.2
5. 12N 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.
Engineering 22 – Engineering Design Graphics
12
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
13
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
14
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
15
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Metric Thread Specification
 Note That Pitch is Stated Explicitly
• Compares to Inverse Pitch (TPI) for
the Unified Specification
Engineering 22 – Engineering Design Graphics
16
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
17
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
18
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
19
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
20
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Threads in Section
 Normal Practice is to NOT Section
the Fastener
Engineering 22 – Engineering Design Graphics
21
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
22
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Forming Tapped Holes
Engineering 22 – Engineering Design Graphics
23
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Pipe Threads
 Pipe Threads have An INTERFERENCE
TAPER that Results in PERMANENT Material
DEFOMATION That (Hopefully) Produces
a Fluid-Tight Seal at the Joint.
Engineering 22 – Engineering Design Graphics
24
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Pipe Thread Representations
 Taper Should be Shown
• Need Not be to Scale
Engineering 22 – Engineering Design Graphics
25
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Pipe Thread Representations
 Only ONE TPI Spec for Pipe Threads
• ASME B1.20.1-1983 = American National
Standard Taper Pipe Thread
 National Pipe Thread (NPT) for Short
• Callout Requires Only the “NPT” Notation,
Along with the “Size”
Engineering 22 – Engineering Design Graphics
26
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
27
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Machine Screw Head Types
 Slot Head Provides More Driving Torque, But Driver
is Hard to Center → Not good for Power Driving
Engineering 22 – Engineering Design Graphics
28
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Threaded Inserts
 Use With Soft Parent Materials Such as
Aluminum, Wood, Plastic, etc.
Engineering 22 – Engineering Design Graphics
29
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
30
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Fastener Design References
 If you design with Threaded Fasteners;
you MUST get access to These Books
 ISBN: 0-8311- 2711-2
Engineering 22 – Engineering Design Graphics
31
 http://www.mcmaster.com/
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Mach-HdBk,
23red Ed Page
1325(of 2511)
Engineering 22 – Engineering Design Graphics
32
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
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
Engineering 22 – Engineering Design Graphics
33
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Building a Fastener
 When I left Watkins-  Let’s Build a A Bolt
Johnson Co. in 2000
from a “Forms” File
We had 775 items in  The Bolt/Screw
our CAD Library
Spec
3/8-16 x 1.25 UNC
SH Cap Screw
Engineering 22 – Engineering Design Graphics
34
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
All Done for Today
Fasteners
Make the
World Go
Round
Molded-In
Inserts for
Plastic Materials
Bolt-Failure by
Reversing-Load
MechanicalFatigue
→ See ENGR45
Engineering 22 – Engineering Design Graphics
35
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Engr/Math/Physics 25
Appendix
f x   2 x  7 x 
9x  6
3
2
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
[email protected]
Engineering 22 – Engineering Design Graphics
36
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Build-Screw Demo - 1
1. Open File New File
using Acad.dwg
6. Find SH Cap Form
and Copy to ClipBd
2. Make Layer “Bolt”
Continuous & GRN
7. Paste SHcap Form
into new dwg
3. Save As 388. Return to Forms
16_125_shcap.dwg
and Copy Detailed
Thread Rep
4. Set Snap to 0.1
5. Open Fastener
Forms file
•
Threaded_Fastener
_Forms_0509.dwg
Engineering 22 – Engineering Design Graphics
37
9. Paste detailed ThdForm into new-dwg
10. Chk Major dia at 1”
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Build-Screw Demo - 2
11. Scale all by Ratio
of 1:0.375
12. 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
Engineering 22 – Engineering Design Graphics
38
16. Offset xline to rt by
•
•
1.25 (scr length)
0.5 (unthd’s shank)
17. Erase Simplifedform lines
18. Stretch shank line
to 0.5 xline
19. Make xline on CL
of Screw
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Early Result
 Just before trimming out unneeded thds
Engineering 22 – Engineering Design Graphics
39
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Build-Screw Demo - 3
20. 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
Engineering 22 – Engineering Design Graphics
40
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
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt
Final Result
 Caveat: Screw HEAD may NOT be toScale 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
Engineering 22 – Engineering Design Graphics
41
Bruce Mayer, PE
[email protected] • ENGR-22_Lec-20__Fasteners-1_Specs.ppt