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Known as the "Doctor of Dimensioning," Alex Krulikowski is a noted educator, author, and expert on Geometric Dimensioning and Tolerancing (GD&T). He has more than 30 years of industrial experience putting GD&T to practical use on the shop floor. Alex has taught GD&T to tens of thousands through his workshops and seminars, and to countless others through his books, self-study courses, videos, and computer-based training programs.
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ETImail 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.
To view past issues of ETImail, see the archives.
Is your company confused about where to start using geometric dimensioning and tolerancing? Do they wonder how much GD&T they should use on drawings? Some engineers fear using too much GD&T. In many cases, the GD&T skills outside of engineering are scarce. This raises concerns that adding GD&T to the drawings may cause confusion in the plants and at suppliers. This mind set causes a prolonged use of the antiquated tolerancing method known as coordinate tolerancing. Some managers feel that they are getting along well using coordinate tolerances. They are afraid to upset the system by introducing the additional complexity of GD&T to drawings. In reality, the organization is often not “getting along” so well. There is often wasted effort trying to meet unrealistic tight tolerances, and the measurement of the parts is left up to assumptions instead of being explicitly defined on the drawing. There are often difficulties with parts from suppliers. In engineering it is difficult, if not impossible, to debug field problems because no one really knows what the tolerance is on the parts in production. Although some may feel that coordinate tolerancing is simpler, it is not. Coordinate tolerancing looks easier to interpret, but it does not address three areas:
Using GD&T does add some complexity to the drawings, because it is more complete. GD&T fully defines the part requirements and, therefore, eliminates the shortcomings of coordinate tolerancing. If the same level of part requirement definition was attempted with coordinate tolerancing, many notes would have to be added, making the drawings much more complex and confusing. GD&T is the most efficient method for defining parts to the level needed for part production. Using GD&T adds three important benefits to your designs:
The fear that the suppliers won’t understand the GD&T is not realistic. I have heard of several overseas companies that have requested their customers add GD&T to the drawings so they can clearly understand the part requirements and know how the part should be measured. When you understand the language of GD&T, you want to realize its benefits as much as possible. Still, some managers are concerned that they do not want to use too much GD&T on their designs. Is there such a thing as too much clarity, too much tolerance for manufacturing, or too much measurement repeatability on drawings? The question becomes how much GD&T needs to be specified? Here are some guidelines that can help an organization use GD&T appropriately:
Each GD&T specification on a drawing will be a direct result of one or more of the above guidelines. The rationale for each guideline is shown in Table 1.
Using these GD&T guidelines will ensure that all the important part features are fully defined for measurement, allow maximum tolerance for manufacturing, and protect the part function. The drawing will clearly communicate the engineering requirements for the part. To download a free "Guidelines for Implementing GD&T" chart in PDF format, click on the image below.
Resolutions or Self Improvement? But in today’s rapidly evolving business world, this kind of tradition doesn’t cut it. Successful individuals must commit to — and consistently deliver on — their promises. Successful individuals need to improve themselves constantly. There’s no such thing as business as usual. I don’t need to tell you that learning is a critical component of this process of self-improvement. You already know that. So instead of adding to a list of traditional resolutions, I am providing you a list of actions to encourage self improvement in an area that is important to our careers. Seven GD&T 1. I resolve to learn more about GD&T. Learning about GD&T is an ongoing endeavor. Each year, we should plan to increase our GD&T skills. Read a new book, a standard, or attend a refresher course. Plan to do something to increase your understanding. If you don't plan an activity, the year will pass and you will not have increased your knowledge. 2. I will use GD&T on all drawings. Many engineers feel that GD&T is only for product drawings, or drawings of high volume parts. This is not true. Many companies use GD&T on low volume parts, gages, tooling, or special machines. The use of GD&T ensures that the parts are fully defined, enables outsourcing, and allows replacement parts to be used.
3. I will mentor two coworkers on the benefits of GD&T. If each person would take the time to mentor two coworkers, the use and acceptance of GD&T would grow. A large part of resisting the use of GD&T is that people do not understand how to use GD&T or the benefits it can provide. 4. I will document examples of where GD&T reduces cost or resolves problems on my designs. One of the roadblocks to getting management to support the use of GD&T is a lack of examples on how GD&T saves the company money. If each person would take the time to document savings that result from using GD&T, its value would soon become apparent to the organization. 5. I will study the part functions when dimensioning a part. An understanding of part function is critical to making decisions about the part dimensioning. Without this information, the dimensioning may not protect the part function and the tolerances will be unnecessarily tight. 6. I will perform tolerance stacks before releasing a drawing. When tolerance stacks are done before the drawing is released, it provides a design that has a much greater chance of functioning properly, has larger tolerances, and has more complete drawings. 7. I will follow the guidelines on "How to Implement GD&T." The guidelines remind us that we should be using GD&T in places we often don't think about on a daily basis. The key to self improvement is self discipline. Self discipline is the bridge between your resolutions and your accomplishments. What you get by achieving your resolutions is not as important as what you become by keeping them. Start today. Remember the old Chinese proverb: A journey of a thousand miles begins with a single step. Good luck.
Alex Krulikowski To download a free "Seven GD&T
ETImail's Standards in the News takes a look at real-life issues involving standards. This month: the importance of standards in life-saving technology. Flaws found in firefighters’ last line of defense U.S. waited 5 years to heed expert’s warning on ‘man down’ alarms Worn by a million firefighters in the U.S., the PASS device is a motion sensor that makes an awful racket if a firefighter stops moving for 30 seconds while battling a blaze. It flashes its lights and lets loose a series of ear-splitting beeps — an urgent call to help a fallen comrade. It’s a call that hasn't always been heard. Tests by federal and independent labs show that some PASS alarms can fail to perform as intended if they get too hot or wet — a serious problem for people who rush into burning buildings with water hoses. And federal investigative reports reviewed by MSNBC.com show that 15 firefighters have died since 1998 in fires where a PASS, or Personal Alert Safety System, either didn't sound or was so quiet that rescuers weren't given a chance to find the firefighter quickly. Tests in a convection oven at the National Institute of Standards and Technology found a problem with the two models it tested: The volume of the beeping diminished substantially at temperatures as low as 300 degrees Fahrenheit — the sort of temperatures that firefighters encounter in a room next to a fire. Researchers said they believe that all of the half-dozen or so brands of PASS alarms on the market would be similarly affected. In addition, some PASS devices made by at least three manufacturers have had problems over the past decade with water leaking into the electronics or battery compartments, causing them to either beep continually or stop working altogether, according to interviews and documents reviewed by MSNBC.com. A tougher new standard for testing PASS devices in heat and water was issued by the National Fire Protection Association in early 2007. But manufacturers said it would be months before an improved device would be on the market. And even when new models are available, there is no plan for recalling the old ones, so fire departments may have to bear the cost of replacing them.
ETI continues to add new products and services that provide you with more GD&T training options. Keep an eye on this section to read about our latest news. This issue highlights the System Approach to Component Tolerancing and the GD&T Trainer Professional Edition, v3.5. System Approach to Component Tolerancing Workshop ETI's new System Approach to Component Tolerancing public workshop will be held in March at ETI headquarters. We can also bring the training to your workplace in an onsite workshop. The workshop focuses on four key areas:
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See the complete list of course topics and more details about this 3-day workshop, here.
GD&T Trainer Professional Edition Version 3.5 Now Available The best GD&T training software just got even better GD&T Trainer adds new features and course LAN, site, and corporate purchasers also receive: The GD&T Quick Reference program - a GD&T reference tool that contains 220 topics covering all aspects of the fundamentals of GD&T. Each topic page shows a detailed graphic and full explanation of the concept. Key GD&T terms are cross-referenced with the Digital Design Dictionary and to paragraphs in the ASME Y14.5M-1994 Dimensioning and Tolerancing Standard. The software can be used to learn the fundamentals or improve upon GD&T skills. It can also be used as a resource when training is done. Read more about it. Click here to see a GD&T Trainer comparison chart. Find out which version of our training software is right for you.
Hello, Mr. Krulikowski, I have a question for you. Can I have more than 3 datum references in one
control frame (more than 3 compartments)? Is this legal? Catia V5 does
not allowed to have more than 3 compartments in one control frame. Thanks.
There are never more than three datum references in a feature control frame. The primary reason for this is the degrees of freedom constrained by each reference; after the third datum reference you are certain to over constrain the feature. There are, however, times when we may see more than three datum features referenced in the datum feature boxes. When A-B appear together in the same box, as in this example, they are considered co-primary datums.
At other times, a feature may have a functional relationship to more than three datum features. Tolerance of position and the profile of a surface tolerance will allow designers to specify multiple single-segment feature control frames. There are some rules for doing this as outlined in my Advanced Concepts of GD&T textbook. The ASME Y14.5M-1994
Standard gives some examples and explanation; however, most users feel that
the standard is more difficult to understand. Again, you will find that even
I have a quick question about reference dimensions. If a character is in parenthesis, is that a designation for a reference dimension? Absolutely, the ASME Y14.5M-1994 makes this clear on page 2 in the definition of a reference dimension. Now the question is, does your drawing reference
the ASME Standard? If not, ISO standards follow the same practice, but they're
called auxiliary dimensions. If the drawing is to be interpreted per some
other standard (such as a corporate standard), then the rules of that standard
must be followed.
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