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Chapter 8: Threaded Fasteners

"Seventy-five percent of the assembly labor cost of an automobile is spent on fasteners.

Eighty to eighty-five percent of all automobile recalls are fastener related."

 - Joseph R. Dudley, V.P. Automotive Marketing, Nylok Fastener Corp.  May 1995



http://www.space.com/11745-loose-bolts-space-station-spacewalkers-trouble.html




Fastening
Two or more components that are joined.  Do not require orthographic views, just the info to purchase the part.

Permanent Fasteners: 
adhesives, welds, braces, solders, rivets, nails.

Non-Permanent Fasteners: 
Screws, bolts, nuts, pins



Notes: http://www.gizmology.net/nutsbolts.htm








https://www.fastenal.com/web/en/78/screw-thread-design






  Thread Characteristics:

Direction
Most are right handed (righty tighty, lefty loosy)


Left handed threads - used where right handed threads would become loose in the application (lawn mower blades)



Lead
Distance traveled during one revolution of the fastener.
Lead = Pitch for single threaded screws.



Double and triple threaded bolts - one revoltuon = 2 or 3 times the pitch. 

Double and triple threading give rapid motion + large thread surface.

Form
Cross-sectional shape, profile.



N - Rounded V profile (rounded for ease of manufacturing)

ACME - Heavy loads, high accuracy
BUTTRESS - High axial loads
SQ - hard to manufacture



Series
Number of threads per inch for a specific diameter.

coarse - general purpose used for holding
fine - to support added force, used in aircraft and automotive industries
extra fine - for short and small diameter fasteners.




Thread spec's:
3 standard representations:



 Class of Fit - How tight fasteners fit together.

Loose fit (1) for harsh corrosive environments.

Regular and Average fits (2) General purpose
Tight (3) For high pressures, stresses, and vibrating systems.


Thread Notes:
Notes on drawing that provide specs about thread.

Use a "leader" to connect note to thread


English Thread:

←0.375-32UNEF-3A-LH
 0.375 = diameter
32 = threads per inch
UN = Form
EF = Extra fine  (could be C for coarse, or F for fine)
3 = class of fit  (1 = loose, 2 = regular, 3 = tight)
A = external thread  (B = internal)
 LH = left handed


Above: Diameter = .25", 28 threads per inch, United National, Fine series, average fit, external, right handed.  (LH would be left handed, nothing written assumes right handed)


Thread Table:
1st column - diameter
(a coarse threaded 1.25" diameter bolt has 7 threads per inch)


Metric:
only listed as coarse or fine.
M - metric

90 - thread diameter
X
6 - pitch (in mm)



Metric threads are usually defined by their pitch, that is, how much distance per thread, inch-based standards usually use the reverse logic, that is, how many threads occur per a given distance. Lead is the distance along the screw's axis that is covered by one complete rotation of the screw (360°). Pitch is the distance from the crest of one thread to the next. Because the vast majority of screw thread forms are single-start thread forms, their lead and pitch are the same.




Tolerance class: 3, 4, 5, 6, 7, 8, 9 + E, G, H.
#3-9 = tolerance grade (larger num = larger tolerance)
6 = medium = most common
Letter = type of fit:
E = loose
G = regular
H = tight





Head:







Work through all of your Chapter 8 WS's!





Experiment with making your own threaded fastener - look through all of Inventor's different thread types etc.


 Try out Manage → Parameters.  This is where you can keep track of your dimensions, and even name dimensions to use them later on.


Right lick on dimension → Dimension Properties → you can show your parameter dimensions


older version:








Revolve around the center axis (Y Axis in my case)









Look through all of the different thread specifications













Try making some of the fasteners out of chapter 8!