Category Archives for Blog

Seven SIlly Things (about GD&T)

This article on GD&T was written by Rick Hughes, a friend of mine from the ASME standards community. Rick was kind enough to let me publish this article on his behalf. I think you will find it interesting.  

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Survey Results on Size Dimensions Based on Y14.5

Introduction

A few weeks ago, I surveyed on the interpretation of size dimensions based on Y14.5.  I posted the survey on several group boards on LinkedIn. This article compiles the results of the  survey.

Before I discuss the results, I would like to thank all the people that participated in the survey. Their contribution allows all of us to look at the questions in this survey from many users viewpoint.

I use these surveys as the "voice of industry" in my work on standards committees. I also believe they are helpful for the readers to know how their use of tolerancing concepts compare to others around the world. 

Purpose of this survey

The purpose of this survey was to find out if various groups in industry interpret and verify the minimum limit (or local size) of size dimensions.as a two point requirement or as a theoretical swept sphere requirement. . (The survey does not address the effects of Rule #1)

GD&T and Inspection Skill Levels of Survey Participants

The figure above shows the GD&T and Inspection skill levels of the survey participants.  This information is important because it shows that most of the responses came from very knowledgeable participants.

Participants Area of Work

The chart above shows that the main two areas of participation were from Engineering/design and quality/inspection. The questions were designed for the engineering community and the inspection community. 

Questions Presented to Both the Engineering /Design and Quality/Inspection Participants

The intent of the question in the figure above is to determine if the participants felt the requirement for the minimum size limit should be verified with a two-point measurement or a theoretical spherical ball.The responses show that the majority (67%) of participants feel that a two-point measurement can be used to verify the minimum limit of a size dimension. However, there is not a uniform interpretation in industry. 

A few descriptions from the "Other" responses on how the minimum size limit should be verified are below. 

  • "Both in inspection two-points and in some cases per Y14.5.1 ball check for a bended tube."
  • "If using a CMM, some points, usually 6, taken around the diameter, the best fit circle taken through the points"
  • "It is my understanding that if you take the smallest two-point measurement of the diameter, it will be the largest theoretical sphere that will pass through the diameter"

The question in the figure above is similar to the previous question about a diameter. It is interesting that when presented with a block even more people selected the response of the two point measurement.

A few descriptions from the "Other" responses on how the minimum size limit should be verified are below. 

  • "The smallest two-point measurement. The term "size dimension" should be clearly defined in Y14.5 in the definition section. It is good timing to include in the next version, it is used throughout the text".
  • "If using a CMM, we would expect measurement  points, to be taken across the surface and a best-fit plane is used - this is good enough for us."
  • "The size of the largest perfect form 2D section that can be passed through the material"

The question in the figure above asked the participants to select an answer based on the Y14.5 -2009 standard. The two point measurement still has the highest response rate. The chart shows there is variation in the interpretation of a size dimension.

Questions presented only to the Quality/Inspection Participants

The figure above shows that the amount of tolerance is the most significant factor in the choice of a measurement device for the minimum limit of a size dimension. I am a bit surprised that the standard referenced on the drawing did not score higher.

The figure above shows the two-point measurement (micrometer/caliper) is the most common method for verifying the minimum limit of a size dimension in industry. closely followed by  CMM verification. I find it interesting that the swept ball algorithm is rarely used.

Conclusions


NOTE:

These survey results are based on participant responses from 27 countries. There were 147 participants total. 61% of the responses were from the U.S. and the remainder from the international community. The highest response rates internationally were from India, Canada, and Great Britain.

Although the participation is significant, it is not high enough to make an accurate assessment of the interpretation of size dimensions in industry, but, it does provide us with information to make useful insights on the topics even though it is not a definitive answer.

The survey results indicate that the minimum limit of a size dimension is not uniformly understood by engineers, designers, quality personnel, and inspectors in industry. The variation in understanding size dimensions is partially because this topic is not covered thoroughly in the Y14.5 and Y14.5.1 standards.

Size can matter

In a number of cases, any of the methods used to verify the lower limit of a size dimension described in this survey would be adequate for the function of a part. However, in certain cases, the method of verifying a size dimension can make a difference between a functional part and a failed product. (e.g. minimum wall thickness, allowable roundness deviation, etc.)

Assumptions are effective barriers to precise communications

If you create drawings, precise communications can make the difference between a  successful product and failure. Where the interpretation of the minimum limit of a size dimension can make a difference in the function of your part, I recommend that you specify how the size dimensions should be interpreted (or verified).

Do you intend the minimum limit of size dimensions to be interpreted as a two point requirement (as implied in Y14.5) or as a  theoretical swept ball requirement (as shown in Y14.5.1)? 

Until the Y14.5 and Y15.1 standards adequately cover how to interpret size dimensions, consider one of the following actions:

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    Add a general note to your drawings to establish a default for how size dimensions are to be interpreted.
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    If your company uses an addendum to the Y14.5 standard,  add a section that documents how size dimensions are to be interpreted/verified. Click here to the read addendum article.
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    Create a measurement plan that covers the method for verifying size dimensions and reference it in your drawings..

Final thoughts

In hindsight, I can think of several additional questions that would have been useful to ask in this survey. It is always a trade-off between the depth and length of these studies. If you have an opinion on how many survey questions would not discourage participants, leave a comment or send me an email. Thanks.

I hope you found the survey results informative. If you like the article, please share it with your friends on on social media. Feel free to leave a comment about your experiences with size dimensions or on any aspect of this article.

Thanks again to all the survey participants.

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Should your company be using an addendum to the Y14.5 standard? Part 3

Part 3 - Tips on creating and implementing an addendum

Introduction

Welcome to part three of the article on addendums. It covers a few tips on creating and implementing an addendum in your organization. How to implement an addendum is just as important as the creation process.

Three types of tips for creating an addendum

This section covers a few tips on creating an addendum. The tips are divided into three parts; useful information, tips for creation, and typical pitfalls to avoid.

1. Useful information for creating an addendum

The list below contains an example of useful information for creating an addendum. All of the items may not apply to your organization.

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    Discourage the use of "extension of principles" beyond coverage of Y14.5 and your addendum on drawings.
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    List the specific standard(s) that are used as a base for your addendum. Include the name and version of each base standard.
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    Provide guidance on how to handle legacy design data with outdated, incomplete, or no GD&T.
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    Include a list of temporary CAD workarounds for areas where your CAD software does not have the new symbols from the latest version of the standard.
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    Include a list of approved template drawings for typical applications.
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    Include a list of quality assurance and metrology standards and practices used in your company
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    Include tips on how to apply tolerances to a drawing. (for example, position tolerances can only be applied to features of size. Rule #1 only applies to individual regular features of size. Also include other tips as needed.)
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    Review the addendum annually to consider and changes requested.
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    Check with your legal department to ensure the addendum is worded correctly and does not cause any legal issues.

2. Tips for creating an addendum

The list below contains an example of useful information for creating an addendum. All of the items may not apply to your organization.

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    Make a presentation to management to get support for the addendum project. The presentation should include: why an addendum is needed, how the addendum will benefit your company's business goals, who are the key stakeholders, and what is involved in creating and implementing the addendum.
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    Create a scope for your addendum. List the topics and base standards that you will include.
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    During the creation process, assemble an addendum team. Involve representatives from all key stakeholders. Typically, the stakeholders include product engineering, supplier quality, metrology, manufacturing engineering, and purchasing.
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    Make the addendum a corporate wide document If necessary, create separate sections for different divisions or locations that have unique needs..
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    Make the addendum an official corporate document (e.g. engineering standard or similar type document.) in your organization with change control and a formal approval process.
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    Include a Y14.5 / ISO standards expert on your addendum team to ensure the addendum is in harmony with the ASME and ISO GPS standards.
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    Add a sentence to your addendum to inform the reader where to send issues, changes, and suggestions.
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    include tips on how to apply tolerances to a drawing. (for example, position tolerances can only be applied to features of size. Rule #1 only applies to individual regular features of size. Also include other tips as needed.)

3. Common addendum pitfalls to avoid. 

The list below contains common addendum pitfall . All of the items may not apply to your organization.

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    Repeating sections of the standard.
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    Using different terminology than in the standard
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    Changing the interpretation of the standard without clearly defining the new interpretation.
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    Forcing the use of the Y14.5 standard on applications where "better" standards exist. (e.g. ISO 10315 Edge Definitions.)
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    Creating new tolerancing tools or methods for applications when tools already exist in the Y14.5 standard.

Tips for implementing an addendum

This section covers a few tips on implementing an addendum. The tips include approvals/buy-in, distribution, and training. All of these tips may not apply to your organization.

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    Require each drawing to have the addendum number in the notes section of the drawing.
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    Develop an internal training program for the addendum and make required for all drawing users.
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    Publish a corporate wide "Notice of Publication" for the addendum.
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    If your addendum changes the interpretation of the Y14.5 standard, distribute it to all of your suppliers. This will help to ensure they have all the information needed to interpret your drawings.
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    Make the addendum available for the public to purchase through a third=party company like Global IHS.

Summary and closing thoughts

Hopefully, some insights were gained with this brief look at addendums. As you may have noticed, I am an advocate of using addendums in large corporations. Developing an addendum renews the focus on the importance of drawings.

In a survey I conducted, I found that about 30% of the companies in the survey use addendums (or some sort of supplement to the Y14.5 standard), and about 15% mentioned that they felt an addendum would be useful in their company.

NOTE:

If you would like to see an example of an addendum, you can purchase a copy of the GM addendum by clicking the button below.

 

Does your company use an addendum? Do you have any suggestions for items that should be in a Y14.5 standard addendum? If so, add a comment below.

If you would like assistance in creating a corporate addendum, contact me at Alex@KrulikowskiConsulting.com 

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Survey Results on the Usage of ISO GPS and ASME Y14.5 Standards.

Introduction

A few weeks ago, I surveyed on whether the ISO GPS or ASME Y14.5-2009 standard is more widely used on drawings in industry. I posted the survey on several group boards on LinkedIn. This article compiles the results of the ISO GPS and ASME Y14.5 standards survey.

Before I discuss the results, I would like to thank all the people that participated in the survey. Their contribution allows all of us to look at the questions in this survey from many users viewpoint.

NOTE:
Since the survey is comparing the use of the Y14.5 (a US standard) and the ISO GPS (an International standard) standards, the results are shown as a comparison of US responses and International responses.

Participation Results

The figure above shows that the International response rate was slightly higher than the US response rate. There were 133 total responses from 27 different countries. The US had 63 responses and their were 70 responses from the International community. The highest response rates of the International participants were from India, Poland, and Brazil.

Type and Size of Industries Surveyed

The survey had participants from a variety of industries. 

The survey responses came from employees working in companies from less than 100 to over 100,00 employees. The chart above shows that 53% of the participants work in companies with more than 10,000 employees.

The first three questions of the survey are focused on gathering information about the participants. Their country and the industry they work in and the size of the company. The next section of the article will explain details about which tolerancing standards are used on drawings in their companies.. 

Current Tolerancing Standards Used on Drawings in US and International Companies.

Whether the ASME Y14.5 or ISO GPS standard is more widely used on drawings is the main question in the survey. My students and customers have often asked me this question. My colleagues in the ISO GPS and ASME standards community talk about it as well.

The survey shows that the ASME Y14.5 standard is widely used (86%) in the US and is used significantly Internationally(56%). 

NOTE:

This survey is based on 133 responses from 27 countries. Although the participation is significant, it is not high enough to make an accurate assessment of the use of tolerancing standards in industry globally. However, it does provide us with information to make useful insights on the use of standards even though it is not a definitive answer.

Survey Participants Recommendation on the use of the ISO GPS or ASME Y14.5 tolerance standards.

Keep in mind; the question below is asking an opinion of the participants.

When asked, "If your company was evaluating which tolerancing standards to use in the future, what would be your recommendation?"

Most of the participants  (67%) responded the ASME Y14.5 tolerancing standard as their preference and both ASME Y14.5 and ISO GPS as their second choice (20%).

The three most common responses from the US participants are below. The standard they recommended is shown in bold. (The number in parentheses is the number of participants with similar comments.)

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    ASME Y14.5 - "We currently use this standard." (12)
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    ASME Y14.5 - "ASME training is a lot easier. Helpful to have nearly all of the info in one document." (9)
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    ASME Y14.5 - "Y14.5 is the most widely used standard." (8)

The three most common responses from the International participants are below. The standard they recommended is shown in bold.(The number in parentheses is the number of participants with similar comments.)

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    ASME Y14.5 -"Easier to understand. Fewer standards. Focused on design intent." (12)
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    ASME  Y14.5 - "Customer requires Y14.5". (12)
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    Both ASME & ISO GPS-"The customer dictates the standards we use"(12)


A few additional interesting comments from individual US survey participants are below.

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     Both ASME & ISO GPS - "I see that ISO shall gain a technical advantage due to GPS approach, whereas ASME is a down to earth shop floor standard."
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    ASME Y14.5 - "ASME Y14.5 is more comprehensive and less volatile. ISO standards may have some elegant solutions; however, I find them very challenging to implement on a corporate and extended enterprise (include supply base) basis."
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    ASME Y14.5 -  "ASME Y14.5 standards are not as complicated as ISO GPS standards over the times about drawings having to refer to multiple versions of standards which are updated and the drawings are assumed to have new interpretations."
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    ASME Y14.5 - "Y14.5 is based on the function of the part. Y14.5 is a complete package, not an unsynchronized collection of many standards like ISO. Y14.5 is less ambiguous than ISO."

A few additional interesting comments from individual International survey participants are below.

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    ISO GPS -"ASME standards are not well spread in European & Africans areas. - Concepts and principles are not at all the same between ASME and ISO.  A Dual life is not realistic. - Theoretically and legally speaking, ASME Y14.5 is a regional standard, not an international one! - "Invocation principle (cf. ISO 8015) gives priority to ISO standards, by default."
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    ASME Y14.5 - Y14.5 is a user-friendly, one book/ISO is a matrix of standards, Y14.5 is revised approx. once per 10 years/ISO standards more frequently. There are enough GD&T books and reference material explaining Y14.5 on the market."
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    ASME Y14.5 - "our company is more than 40 years old. At the beginning, we used ISO standards since 2001. We are using ASME Y14 but we have some old drawings with ISO standard, we realize that is is better to use just one standard and we chose ASME as our standard

Conclusion


Based on the survey responses, I feel that the survey suggests three things:

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    The ASME Y14.5 standard is used in the US and Internationally and is the preferred standard by most of the survey participants.
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    The ASME Y14.5 standard is easier to learn and easier to use than the ISO GPS standards. The ease of use of the ASME Y14.5 standard coincides with my experience in working with standards in industry.
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    The multiple standard approach of the ISO GPS standards seems to be problematic for industry. However, the completeness of the ISO GPS standards may provide a technical advantage over the ASME Y14.5 standard.

I hope you found the survey results informative. If you liked the article, please share it with your friends on Linkedin. Feel free to leave a comment about your experiences with these standards or on any aspect of this article.

For all of my colleagues in the ASME and ISO standards committees, I am just the messenger of the survey responses.

Thanks again to all the survey participants.

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Should your company be using an addendum to the Y14.5 standard? Part 2 – Five Content Categories of an Addendum

Introduction

This part of the article on addendums to Y14.5 covers the five categories typically found in an addendum.

Throughout this article where a number appears between square brackets, e.g. [xx], it refers to the paragraph or figure that is being modified from the ASME Y14.5-2009 standard.

There are five categories of content commonly found in corporate addendums. 

1. Allow the use of only one of several optional methods.
2. Change a default condition.
3. Clarify a concept, symbol, modifier, or definition for your companies' application.
4. Discourage/disallow the use of a concept, symbol, or modifier.
5. Document the use of a tolerancing practice that is not in the Y14.5  standard toolbox.

Examples of modifications in each content category are in the paragraphs below. Corporate addendums may include many or just a few modifications.  This article contains a few examples of modifications that are common in addendums.

The format of an addendum varies in each company. The format shown here may not be optimal for your company.

The examples in this article are not arranged in the sequence of a typical addendum. The examples are grouped by category.

The first category: Allow the use of only one of several optional methods. 

This content category is popular in addendums. Selecting an option when several practices are permitted in the Y14.5 standard is important because it helps to create consistent drawings and reduce confusion.

The list below contains a few examples of selecting an option from the Y14.5 standard.

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    The use of SI metric (mm units) is recommended [1.5]
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    Angular units shall be specified using decimal degrees [1.5.5]
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    Unless otherwise specified, all dimensions apply after heat treat and surface coatings [2.4.1]
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    Where the location of datum targets are defined with dimensions,  basic dimensions shall be used [4.24.7].


The second category: Change a default condition.

In most cases default conditions are not revised in an addendum; they are addressed on the face of a drawing.  What should be in an addendum is a list of which defaults should be overridden on your drawings and instructions on how to override them.

Changing a default can be beneficial because the default may not be the best for your company. For a list of common defaults in the Y14.5 standard, check out the blog article "Do you know which ASME Y14.5-2009 defaults apply to your drawings?")    Click here to read the defaults article

If the default conditions are not the same for all types of parts in your company, the addendum should show what parts should have defaults overridden and how to denote the override condition.

The advantage of revising standard defaults on the face of a drawing is that the requirement or condition is visible to the drawing users.

The third category: Clarify a concept, symbol, modifier, or definition for your companies application.

Clarifying concepts from the Y14.5 standard is important because it reduces confusion by providing additional explanation of items that are not fully explained in the standard.

The list below contains a few examples where clarifying a concept from the Y14.5 standard could be in an addendum.

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    Where the Independency symbol is applied to a size dimension of an external feature of size, and a form control is applied to one of the surfaces, its outer boundary of the feature of size shall be determined by the MMC of the feature of size plus the effects of the form control. [2.7.3]
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    A few terms that you may want to clarify with your addendum are: element, continuous feature, free state, and define what UOS means on a drawing and how to determine when is it overridden. [1.3]
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    Clarify whether surface texture is included in size tolerances and geometric tolerances. For a discussion that shows the different interpretations in industry check out the article "Survey results on the interpretation of the ASME Y14.5 standard"   Click here to read the article
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    How to designate and interpret a complex curve as a datum feature. [4.1]
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    Document the standards that apply to your drawings. The standards cited in this paragraph apply at the date shown. Any newer version shall not apply unless explicitly stated in this addendum. If a conflict exists between the text any of the standards cited and this addendum, the text of this addendum shall take precedence. [1.2]

NOTE:

Each ASME standard contains a paragraph citing a list of additional standards it invokes and provides a method to determine which standards are partially invoked.

However, many companies have difficulty understanding exactly which standards, and which versions apply to their drawings.

The fourth category: Discourage/disallow the use of a concept, symbol, or modifier.

Discouraging or disallowing the use of a symbol or concept is important because it reduces the number of tolerancing tools available for use on drawings. There are many tolerancing tools in the Y14.5 toolbox that are not needed for some types of parts. There are also tolerancing tools that are not used often.

There are subtle differences between some of the GD&T symbols. There are often discussions over which symbol is better for an application. The addendum focuses the discussions by disallowing or discouraging certain tolerancing tools leaving the tolerancing tools needed for defining your products.

Tolerancing tools can be disallowed for a variety of reasons. A few tolerance tools are overly restrictive for most applications or are not a good tool for your companies' applications. A few tolerancing tools that are only used in rare applications may be disallowed or discouraged to prevent their widespread use.

The list below contains a few examples of disallowing or discouraging a concept, symbol, or modifier.

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    The concentricity symbol shall not be used. [7.6]
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    The symmetry symbol shall not be used. [7.7.2]
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    The Statistical Tolerance modifying symbol shall not be used. (3.3.10)

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    The "alternative practice" to control parallel and perpendicular relationships shall not be used. [6.6]

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    Direct tolerancing (often referred to as plus and minus or limit tolerancing) methods shall not be used for location or orientation of features of size. [2.2]

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    The practice to override the degrees of freedom by reference of an order of precedence shall not be used. [4.22]

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    The method of specifying datum features at LMB shall not be used. [4.11.7]
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    The method of multiple LMB's shall not be used. [4.11.8]

NOTE:

Another area that I recommend companies to address is to discourage "extension of principle" on their drawings when a tolerance application is not in the Y14.5 standard or in their addendum. Even though the extended principle may make sense to the drawing creator, since its interpretation is not documented, it can be interpreted differently by drawing users.

The fifth category: Document the use of a tolerancing practice that is not in the Y14.5 standard toolbox.

Documenting the use of a symbol or concept that is not covered in the Y14.5 standard is important. It helps drawing users to have a consistent interpretation of the drawing requirements. If you add a new symbol or concept, it should be fully explained from a functional and inspection standpoint. 

The list below contains a few examples of tolerancing tools that are not in the Y14.5 standard but may be needed. In this section, only example topics are listed, the entire addendum text and figures to fully describe these items are too lengthy for this article.

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    A method to define a uniform Thickness/Gap Tolerance. (e.g. a wall thickness.).
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    How to designate a wedge as a datum feature.
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    When and how to document restraint conditions.
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    The Free-State modifier along with Restraint notes may be used on both non-rigid parts as well as rigid parts when specific assembly conditions must be met. (e.g. the flatness of sealing surfaces.)
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    A method to specify how to restrain datum features.
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    How to dimension cylindrical parts with bends (e.g tubes).

Caution

Adding new tolerancing tools in your addendum should be used sparingly. Adding new tolerancing tools can cause problems for CAD, analysis, and inspection software.

Summary and closing thoughts.

In part two, we looked at each of the five content categories of corporate addendums. Each corporate addendum is different based on their unique situation. Every addendum will not address all five of the above categories. An addendum may also include additional information not discussed in this article. 

Part three of this article will be posted next week. In part three, you will learn a few tips on creating and implementing an addendum in your organization.

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