Known as the "Doctor
of Dimensioning," Alex Krulikowski is a noted educator, author, and expert
on Geometric Dimensioning and Tolerancing (GD&T). A design manager
with one of the world's largest manufacturing corporations, he has more
than 30 years of industrial experience putting GD&T to practical use
on the shop floor.
Larry Adams takes
a look at today's trend towards computer-based learning technologies and
the potential savings it produces in the April 2000, Quality Online
To read more about it,
Professional Certification Available
ASME has established
a certification program for GD&T Professionals. The GDTP Certification
Program provides the means to recognize proficiency in the understanding
and application of GD&T principles. Click
Keep up to date with
issues pertaining to the ASME standards, with Mechanical Engineering Online.
Instructor's Kit Goes Digital
ETI launches its new
Digital Instructor's Kit--all the course materials an instructor needs
to teach an entire GD&T course included on one handy CD-ROM.
To read more about
To download a demo,
Offers On-Site Training
Find out more about what ETI has to offer your organization.
Tech Calendar Now On Website
Stay up to date on the latest industry news with the
ETI Tech Calendar.
is a regular online publication devoted to Geometric Dimensioning
& Tolerancing. Each edition features a host of GD&T resources
you can link directly to, as well as dimensioning tips by noted GD&T
author and ETI founder, Alex Krulikowski. We also invite you to visit
our website, www.etinews.com.
Eliminating the Confusion:
The Nine Rules for Composite
Position Tolerancing is a confusing topic.Y14.5M-1994 dedicates about 35
pages to explain it. I have condensed the Y14.5 description into this set
of Rules for Composite Tolerancing. These nine rules can help to determine
if a composite position control is properly specified or is being properly
interpreted. The Rules are extracted from my textbook, Advanced
Concepts of GD&T.
The Pattern Rule
A composite position control
must be applied to a set of multiples features of size (i.e. a pattern
of holes, coaxial diameters, etc.).
The Segment Rule
A composite position control
can only contain two segments (the PLTZF and the FRTZF).
The Upper Segment Rule
The upper segment can and
must control the location and/or orientation of the pattern.
The Lower Segment Rule
The lower segment can and
must only control the spacing and/or orientation of the pattern.
The Tolerance Refinement
The tolerance value of the
lower segment must always be a refinement of the tolerance value of the
The Basic Dimension Rule
Basic dimensions (specified
or derived) that define location of toleranced features apply to the upper
segment only. Basic dimensions (specified or derived) that define spacing
and/or orientation apply to both segments.
The Datum References Rule
Any datum references and
datum modifiers in the lower segment must be repeats and in the same order
of the datum references and datum modifiers of the upper segment.
The Segment Verification
Each segment of a composite
position control must be verified separately.
The Separate Requirement
The simultaneous requirement
default does not apply to the lower segment of composite position controls.
||In the next issue of ETImail:
Nine Myths of GD&T
Standards in the News
you ever notice how many news stories focus on unsafe buildings or transportation
safety? How about the problems auto makers are having? How many times have
you purchased something, only to find out that is was flawed, inoperable,
or poorly constructed?
Standards are important
to keep our lives safe and functional. When they're not met, we end up
fixing errors, repairing problems, and righting wrongs--even putting our
lives in jeopardy.
a look at real-life issues where standards have failed or need improvement.
This month: the Mars Climate Orbiter fiasco.
Excerpts from the Jet Propulsion
Laboratory Website http://www.jpl.nasa.gov/
MARS CLIMATE ORBITER TEAM
FINDS LIKELY CAUSE OF LOSS
When the Mars Climate Orbiter
project failed in 1999, NASA's Jet Propulsion Laboratory internal peer
review team went to work to discover the problem. Their preliminary findings
indicated that, "A failure to recognize and correct an error in a transfer
of information between the Mars Climate Orbiter spacecraft team in Colorado
and the mission navigation team in California led to the loss of the spacecraft
"People sometimes make errors,"
said Dr. Edward Weiler, NASA's Associate Administrator for Space Science.
"The problem here was not the error, it was the failure of NASA's systems
engineering, and the checks and balances in our processes to detect the
error. That's why we lost the spacecraft."
"Our inability to recognize
and correct this simple error has had major implications," said Dr. Edward
Stone, director of the Jet Propulsion Laboratory. "We have underway a thorough
investigation to understand this issue."
The project failed at a cost
of hundreds of millions of dollars. Here's the breakdown:
$327.6 million total for
both orbiter and lander (not including Deep Space 2)
$193.1 million for spacecraft
$91.7 million for launch
$42.8 million for mission
THE REST OF THE STORY.
This expensive mistake had
an unbelievably simple cause--a failure to make certain which standard
of measurement was being used: one team was using the metric system, while
the other was using English units of measure. Here's a quote from the peer
review report: "Findings indicate that one team used English units (e.g.,
inches, feet and pounds) while the other used metric units for a key spacecraft
operation. This information was critical to the maneuvers required to place
the spacecraft in the proper Mars orbit." Full
|Mars Climate Orbiter
and its sister mission, the Mars Polar Lander, are part of a series of
missions in a long-term program of Mars exploration managed by the Jet
Propulsion Laboratory for NASA's Office of Space Science, Washington, DC.
JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO. JPL
is a division of the California Institute of Technology, Pasadena, CA.
like information on "simultaneous requirement default." Is this subject
covered in Y14.5 or in any of your materials?
The ETI Mailbag
on "Simultaneous Requirement Default" is in sections 18.104.22.168 and 22.214.171.124
of the Y14.5 dimensioning and tolerancing standard. It is also covered
in Chapter 18 of the Advanced Concepts of GD&T textbook.
for the USCAR Y14.5 addendum for the auto industry. I have been to their
web site and could not find it. Can you help?
USCAR Y14.5 addendum is a little bit tricky to find. I will tell you where
to go to get the GM version of the USCAR addendum, but I'm not sure where
the Ford and Chrysler versions are located. The GM version is located on
the following website: www.gmsupplypower.com
-- click the "Search Tool" link on the right hand side and it will take
you to the search page. Type in "dimensioning and tolerancing addendum"
in the search window. It will take you to a page listing all the different
addendums. The one you are looking for is probably the first entry called
Global Dimensioning and Tolerancing Addendum, 2001. It is a free download
in ZIP format, and the addendum is in a Microsoft Word format.
would appreciate it if you'd keep us in mind when
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