OF Homework
DESIGN ENGINEERING SYSTEMS I
April 14, 2011
Threaded Fasteners and Power Screws
Functions
Fasteners: mechanically joins or affixes two or more objects
Figures from http://www.nutsandbolts.com/
Power Screw: convert rotation to linear motion
http://www.absoluteastronomy.com/
topics/Jackscrew
http://millingmachinesreviewblog.blog.gy/2010/06/
08/zen-toolworks-cnc-carving-machine-diy-kit-7x7/
DESIGN OF ENGINEERING SYSTEMS I
http://knightvision.calvin.edu/bbcswebda
v/orgs/ENGR/senior-projects/200708/Team03/Album/index.htm
April 14, 2011
Standard Thread Forms
Key parameters and terminology
Major, Minor, and Pitch Diameters
Pitch diameter is the diameter of a theoretical cylinder that passes through the threads in such a way that the distance
between the thread crests and thread roots is equal. In an ideal product, these widths would each equal one-half of the
thread pitch
Thread Pitch
Included Angle
http://www.fastenal.com/web/services.ex?action=
FEDS&article=ScrewThreadDesign
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Standard Thread Forms
The thread is define as
1
-20
4
UNC -2 A (tolerance level, external/internal)
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Standard Thread Forms
The thread is as
6 define 0.75
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Tensile Stress Area
A measure approximating the smallest possible fracture area
2
( + )
=
4
2
=
http://www.tribology-abc.com/calculators/e3_6d.htm
http://www.bestbolt.com/white_papers/white_paper_06.pdf
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Power Screw
Lead screws or translation screw
large mechanical advantages for lifting and moving large loads
Accuracy
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Applications
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Force and Torque Analysis
Chapter 10.3
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Example
Determine the lifting and lowering torque and the efficiency of power screw using ACME
screw and nut. The axial load 10000 lbs. The mean collar diameter is 2 in. The coefficients
of friction are estimated as 0.13 and 0.10 for f and fc .
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Example
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Example
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Example
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Power Screw and CNC
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011
Power Screw and CNC
DESIGN OF ENGINEERING SYSTEMS I
April 14, 2011