Known as the "Doctor
of Dimensioning," Alex
Krulikowski is a noted educator, author, and expert on Geometric Dimensioning
and Tolerancing (GD&T). As a design manager with one of the world's
largest manufacturing corporations, he gained more than 30 years of industrial
experience putting GD&T to practical use on the shop floor.
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ETI offers a special
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GD&T Trainer Professional Edition (Y14.5M-1994) contains 28 student-focused
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Y14.41 - 2003
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seldom improve quality by cutting costs, but you can often cut costs
by improving quality.
James Myers, Manager
is a regular online publication devoted to Geometric Dimensioning &
Tolerancing. Each edition features a host of GD&T resources and links,
as well as dimensioning tips by noted GD&T author and ETI founder,
Alex Krulikowski. We also invite you to visit our website, etinews.com.
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to a feature:
Article: Math-based development
processes and Y14.41
in the News: A
tolerancing issue causes bicycle lock problems
ETI Mailbag: Design
intent issues, true position RFS, sectional
Great resource about how
to develop optimal
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Features: Quality Quote of the
Development Processes and Y14.41
new ASME Y14.41-2003 Standard on Digital Product Definition Data
Practices establishes requirements for preparing, organizing and
interpreting 3-dimensional digital product images. As chairman of
the committee that developed the standard, I am often questioned
about its definition, application, and benefits. In this month's
article, I'll answer 10 questions about Y14.41.
The official explanation by ASME says:
ASME Y14.41, Digital
Product Definition Data Practices, advances the capabilities of ASME
Y14.5M, Dimensioning and Tolerancing, the widely used standard pertaining
to 2-D engineering drawings. ASME Y14.41 defines the exceptions as well
as additional requirements to existing ASME standards for using product
definition data or drawings in 3-D digital format.
several industries were involved in developing the new ASME Y14.41 standard,
including automotive, aircraft, heavy equipment and CAD software manufacturers.
chairman of the committee, what was most unique about the development
The committee developed the standard in six years. Normally,
standards are produced over a 10-12 year period. Industry needed this
so badly, and technology is changing so fast, we accelerated the standard
development to accommodate the needs of industry.
is Y14.41 needed in industry?
For over a decade industry has been moving toward tolerancing solid models
rather than creating two-dimensional drawings. Prior to ASME Y14.41, there
were no standards that covered the display of tolerance information on
There are two important
reasons why Y14.41 is critical to industry:
The need to tolerance 3-D models and simplified
ASME Y14.41 advances the capabilities of the Y14.5 Dimensioning and Tolerancing
Standard that is used on 2-D engineering drawings. Y14.41 defines the
exceptions as well as additional requirements to existing ASME standards
for using product definition data or drawings in 3-D digital format. The
development of the ASME Y14.41 Standard was initiated at the request of
industry and the US Government.
need to migrate to a math-based product development process
The continuing pressure to bring products to the marketplace in less time
and for less cost is requiring many companies to automate their product
development processes. Many companies are migrating towards a math-based
product development process, which includes four major components:
are entered once.
This saves labor by eliminating the need for reentry of data. It also
eliminates errors from reentry and misinterpretation.
2. Part tolerances are capable of being electronically interpreted.
This eliminates errors from human interpretation of geometric tolerances.
3. The digital data set (a set of model files) is the single source
for all information regarding the part.
This allows easy access to up-to-date information and reduces errors.
4. Data is linked and updated automatically.
This saves labor and reduces errors from manually updating information
when a change occurs.
These major components
result in significant savings in the time it takes to develop products
as well as developmental costs.
the role of standards in a math-based product development process?
Standards play a key role in achieving a math-based product development
process. In order to automate the development tasks, the product information
needs to be electronically interpretable. Three factors must be met:
- Product information
needs to be described in accordance with a single standard.
- The standards used
must be mathematically robust.
- Companies will
need to follow national standards and abandon local practices.
important is Y14.41 to a math-based product development process?
Y14.41 is an important standard in migrating towards a math-based product
development process. All the efforts I have seen in industry involve eliminating
traditional 2-D drawings. Y14.41 documents and standardizes a method used
by many companies where a partial drawing is released with a model. It
also sets the foundation for eliminating drawings and showing tolerances
directly on a model.
does Y14.41 help communication in an organization?
Engineers, manufacturers, and suppliers can use Y14.41 to communicate
model tolerances in a standard way. If two companies show model tolerances
differently, the user will have problems finding them on the drawing and
knowing how to interpret them. Also, without the new standard, it would
be impossible to translate tolerance information from one CAD system to
are the major new concepts in the Y14.41 Standard?
There are too many new features to list here, so I'll highlight a few.
The major contribution of the standard is in defining how to display tolerances
in a data set, and it does so through two methods:
1: Displaying the tolerances directly on the model. Figure
1 shows an example of displaying tolerances on a solid model.
2: Displaying tolerances on axonometric views of a model in a drawing
plus model data set. Figure 2 shows an example of a drawing
that shows only the tolerances for the part. The model would contain the
The standard converts
geometric tolerances from a 2-D language into a 3-D language. It defines
over thirty terms used in solid modeling. The standard also establishes
rules for converting model values to part dimensions.
does Y14.41 benefit manufacturing?
The new ASME Y14.41 standard can benefit anyone who manufactures parts
and uses electronic data. The standard enables manufacturers to implement
math-based manufacturing processes. There are many significant savings
available to manufacturing organizations if they can automate the design,
analysis, and inspection of parts using math-based tools.
does ASME Y14.41 impact the global economy?
While ASME is a North American organization, its standards are becoming
global. Standards have a different role than they did years ago, when
they were used primarily in the country in which they were developed.
Companies now have plants all over the world, so when a major corporation
adopts a standard, the standard is used internationally.
With standards being
developed and published in several countries, the challenge is how to
harmonize them. Suppliers to major companies often have to work with two
or three standards to satisfy their customer requirements. The faster
we arrive at one standard, the better it will be for industry. The Y14.41
standard has been submitted to the ISO organization for use in creating
an international standard.
are the major issues facing industry in migrating to a math-based product
There are several tools that need to be improved upon and harmonized for
industry to truly achieve a math-based process. I believe these areas
need to be addressed to make math-based developmental processes practical
on a wide scale:
The Y14.41 standard is a start, but there is much work to be done nationally
and internationally. Harmonization and becoming mathematically robust
are two major gaps in standards today. Closer adherence to standards by
industry is also an issue that needs to be resolved.
Hardware used for CAD is generally too expensive. To have widespread use
across all departments in thousands of companies, the hardware needs to
be more affordable.
Three areas need to be addressed:
Cost - There
is a tremendous difference between CAD software prices. The high-end
software packages need to become affordable for smaller companies.
- The software developers need to focus closely on standards. They should
encourage customers to use standard specification and discourage customer
requests to add features to software that are not compliant with published
standards. If this practice continues, it will undermine the standards
and hinder the migration to math-based processes.
Complexity - If we are to achieve widespread use of the software,
it must be simpler for the user to work in the system. Currently, it
can take 6-8 weeks to train a new user. This is not practical for widespread
use of the tool.
The data translators need to be able to translate tolerances in addition
to model geometry. Without complete data translation, we will not be able
to communicate data across companies. If we had robust translators, companies
could work in the system of their choice.
One of the most important ingredients to change is the culture of the
workforce. The math tools can be perfected, but if the culture isn't ready,
progress will be slow. Management needs to actively work on developing
a culture that embraces and trusts math-based tools. There is a lot of
talk about this in industry, but the actions of many management teams
do not support cultural change.
can I gain a better understanding of the new standard?
presented an eight hour seminar on the new standard at the ADDA 45th Annual
Technical Conference, in Huntsville, Alabama. ETI is now offering a Solid
Model Tolerancing workshop to companies that desire a better understanding
of the standard and its application. For more information about the course,
here, or contact ETI at 800-886-0909 to schedule the new onsite workshop.
For information on
how to order the ASME Y14.41 Standard, visit the ASME
Alex established a digital tolerancing forum to discuss issues related
to tolerancing of solid models. The forum shares information on
the capabilities, technical and implementation issues, and uses
of digital tolerance information. More information about joining
the forum can be found at http://www.etinews.com/dig-tol-forum.
welcome your feedback. Send comments about this article to ETImailbag.
Your opinions will be posted in the next issue.
This article may be reprinted free for use by
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Policy is followed.
Standards in the News takes a look at real-life issues involving standards.
This month: a tolerance issue impedes product performance.
Excerpt from the wired.com
A PEN, OPEN A LOCK
in the News looks at current issues regarding the use of standards and
the problems that result from their misuse. This issue highlights an article
by Leander Kahney in Wired News.
A 50-year-old lock
design was rendered useless last week when a brief post to an Internet
forum revealed the lock can be popped open with a cheap plastic pen.
On Sunday, bike enthusiast
and network security consultant Chris Brennan described opening an expensive
Kryptonite bike lock using a ball-point pen. Wired News tested Brennan's
claims. A brand new Kryptonite Evolution 2000 was opened in seconds using
a Bic pen. After cutting four small slits in the end of the pen's barrel
to ease it in, the lock opened with a single twist.
Brennan, 24, of San
Francisco, said he successfully opened two Kryptonite locks, an Evolution
2000 and an older Kryptonite Mini lock. Subsequent
posts to Bike Forums and other websites report the vulnerability applies
to many of the company's cylindrical-lock products, including some from
Kryptonite's vaunted New York series.
The New York line
carries a $3,500 replacement warranty in the event of theft, and Kryptonite
claims the locks are resistant to "bolt cutters, saws, hammers and
"That's the absurdity
of it," Brannan said. "It's not picking the lock or smashing
it open. It's the absurdity of a small piece of plastic breaking your
is from the article, "Twist a Pen, Open a Lock," by Leander Kahney,
in the September 17, 2004, issue of Wired
News online. Copyright 2004, Lycos, Inc.
am stuck between engineering and quality on the following issue. The drawing
shows Datum 'B' , but the problem is that quality and inspection say that
the defined datum 'B' is the bottom edge of the part, while the engineer
states that design intent is that datum 'B' is defined by
the centerline of the part.
Click on image
for larger view.
have a symmetrical part design in which the design intent is to use a
center line as a datum feature. The notation of this datum feature is
defined on the extension line of a standard dimension.  Is this the
correct notation per ASME 14.5M-1994? Or,  does the dimension need
to be basic so that the datum feature cannot move per tolerances? (Ref.
ASME 14.5M-1994 pg. 61 fig. 4-11, 4-13.)
other suggestion is to simply remove the dimension from the location of
the datum identifier so that there is no confusion.  How do you perceive
this design intent per ASME 14.5M-1994. Also note section 4.3.2 "Datum
feature Identification." Your comments and suggestions are greatly
Jackson, Project Leader
De-Icing & Specialty Systems
like a lot of confusion going on over how to interpret the drawing specifications.
It is amazing how much time can be spent debating tolerance specifications
when the drawing isn't clear or the people interpreting the drawing are
not skilled in reading tolerances.
There were three
questions in your email. The answers are:
Answer 1 - Yes,
datum B is specified correctly as the centerplane. On the drawing you
submitted, datum B is the centerplane (of the true geometric counterpart)
of the 2.75 dimension. In Y14.5, it denotes that when the triangle from
a datum feature symbol is in line with a dimension, the datum is derived
from the centerplane of the dimension. The 2.75 feature of size is considered
the datum feature, and the datum becomes the centerplane (true geometric
counterpart) of the feature of size dimension. Since the datum feature
is being referenced at RFS, the datum feature simulator would be two parallel
planes that contract about the 2.75 width. The center plane of the datum
feature simulator is used as the datum.
Answer 2 - I believe
you are referring to the 2.75 dimension. This dimension does not have
to be basic. (Also, the basic 1.375 dimension is not necessary on this
Answer 3 - The
figures (4-11, and 4-13) show methods for denoting the center plane as
a datum feature and support answer 1.
You didn't ask,
but I thought it is worth mentioning: I noticed position tolerance on
the elongated holes is specified incorrectly. Consider using the method
shown in Y14.5 in figure 5-47.
am being asked to inspect true position RFS. The true position tolerance
is 0.010". I understand that this is a circular tolerance zone with
a diameter of 0.010 with its center at the datum. I measure the dependent
feature and find that its centerpoint is 0.006 away from the datum.
this part rejectable? What number do I write on my inspection report?
Is it the 0.006 distance (while still rejecting the part?), or do I report
0.012 (like the diameter of the 0.006 distance)?
you for your time,
are correct. The part described should be rejected. I would designate
in the inspection report that the tolerance zone allowed was .010 DIA,
and the hole location was .012 DIA. Typically, we report the hole location
in the same terms as the allowable tolerance zone.
Y14.3-1994, paragraph 3.2.4 states that the cutting plane should be shown
thru an exterior view and not thru a sectional view. Is this a hard and
fast rule? On some drawings, taking a section off of a section seems like
the best approach for clarity. Your comments?
Paul Reed, Design
General Atomics Aeronautical Systems, Inc.
The practice of cutting a section from a section has seemed to grow in
many companies over the last five years. You are correct; it is not in
accordance with ASME Y14.3, but it seems to be fairly common in industry.
My only thought is to make sure the drawing is clear when using this practice.
appreciates your questions and comments.
Send your GD&T questions to: ETImailbag.
teaching ideas to new products that will assist you in training or on the
job, the ETImail Tech Tip will keep you informed about new technology and
training trends. This month's Tech
handbook about optimal tolerance specifications.
MANUFACTURING AND GAGING ISSUES
tip is for all the "geotolophiles" out there. (Note: A geotolophile
is a person who can't get enough geometric dimensioning and tolerancing.)
I found an excellent book on tolerancing no, not a GD&T book,
but a handbook on how to develop optimal tolerance specifications. The
book is Tolerance Design: A Handbook for Developing Optimal Specifications.
It was written by Clyde M. Creveling, (Prentice Hall PTR, 1996). This
is the most extensive work I have found on developing tolerances.
Here is brief excerpt
from the preface:
This book covers
the three initial phases of the product-development process where tolerance
development resides as the final cost-versus-quality balancing process.
It explains, in detail, how tolerance design relates to concept design
and parameter design. It also relates the tolerance design process to
many other engineering and product development tools and tasks, including
reliability growth activities.
The book is not for
everyone. It is very analytical and includes a number of mathematical
formulas used in tolerance development. However, if you are a geotolophile,
you will find this book a valuable reference. I highly recommend it.
A Handbook for Developing Optimal Specifications is available at various
online bookstores. To see a list of a few of them, click
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