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Written, with help from students and clients,  by James D. Meadows
The Tolerancing Newsletter January, 2007

 

            Before I begin to answer technical questions in this newsletter, let me tell you about my two new books.  One was written in response to a question which doesnít appear in this newsletter.  It was from a gentleman who asked why there were no books comparing the ISO and ASME dimensioning and tolerancing rules and symbology.  Other than a very short, very outdated pocket guide, he was right.  There was nothing I could find on the topic.  So, I wrote an 80 page, absolutely up-to-date book on that very subject.  Since the book references about 20 different standards and technical reports, it will constantly be updated as new standards are issued.  But as of today, it is the latest word on Differences and Similarities between ASME and ISO Dimensioning and Tolerancing Standards.

 

            The other book, entitled Geometric Dimensioning and Tolerancing in 2007, is 537 pages long and is meant to take the place of my other textbook on GD&T, which was published in 1995.  Although both books are still current and comply with rules in the most current ASME Y14.5M-1994 standard, the GD&T in 2007 textbook offers some insights and information not contained in the other book.  For example, it quotes rules found ASME Y14.43-2003 on Dimensioning and Tolerancing Principles for Gages and Fixtures, and ASME Y14.41-2003 on Digital Product Definition Data Practices.  It also covers a lot of information on tolerance stack-up analysis and statistical tolerancing methods and specificity that are not found in my 1995 GD&T textbook

 

            Below, Iíve included a single illustration from each of my new books.  The first is a charted comparison of controls commonly used on round surfaces from Geometric Dimensioning and Tolerancing in 2007.  The second is a chart of symbology from ISO 1101:2004 and explained in Differences and Similarities between ASME and ISO Dimensioning and Tolerancing Standards.

 

 

Geometric Dimensioning and Tolerancing in 2007, by James D. Meadows (537 pages).

 

 

Differences and Similarities between ASME and ISO Dimensioning and Tolerancing Standards by James D. Meadows (80 pages).

 

 

            For further information on either of these books, please see Online Store page.  Now, on to the technical questions.

 

 

Subject: Question on Reporting Position

 

Hello Jim,

      We are having discussions with Chrysler Dimensional Engineering group
(Contracted by Chrysler from QMC out of Auburn Hills) on how true position should be reported.

Say we have a feature frame

 (Position / Diameter of 6mm at MMC / A-D / B at MMC /C).

We report this giving the actual and deviation from nominal in X, Y, and Z
Nominal     Actual            Deviation
X - 175.67  177.83            2.16
Y - 89.02   90.05               1.03
Z - 444.62  444.89              .27

Then we also report the actual true position which is also considered the
deviation as 0 would be best, but you can have up to 6
Nominal                 Actual
Diameter of 6           2.12

Chrysler is stating that this should be reported in two ways
      1) deviation from nominal for position
      2) radial position

Our problem is the feature control frame calls this feature a diameter so
with the print being the bible in this instance how can we report radial.

Any ideas or suggestions?  Is there a standard in ASME Y14.5M-1994 that I am over looking for reporting?  Is there an industry standard?

Thanks in advance
Mark

 


Mark,

 

There is no standard that dictates how you report deviations from true position.  You can report it in any way that best serves your organization.  At any rate, I don't see a problem with reporting the allowed tolerance (which is stated, as you say, as a diameter in the feature control frame) as either a radius or a diameter.  As long as everyone knows that you are either speaking in radii or in diameters, there is no real difference.  So, if you are allowed a diameter of 6 mm, you can say you are allowed a radial deviation from true position of 3 mm.  If you are out of position a diameter of 2.12 millimeters, you can say you are out of position a radius of 1.06 millimeters. 

    

As long as everyone agrees to report in either diameters or radii, it just doesn't matter.

Jim

 

Subject: Question on Whether the Box Goes Around the Number of Features When Using Basic Dimensions

 

Jim,

Our group has your VHS tapes of your Fundamentals of GD&T training and they've been extremely helpful in teaching me the basics of GD&T.  One question that is causing some discussion within the group is whether it is correct to put the 3x (for example) within the boxed (basic) dimension (if three features all are the same distance from a datum plane) or if it must stay outside the box?  Or if it even necessary as in the ASME Y14.5M-1994 standard on pg 107 they aren't calling out the number of features (e.g  three holes 6.4 up from B) at a specific dimension.

 
Thanks for the website and any comment you're able to send our way.


Derek

Lawrence Berkeley National Laboratory

 

 

Derek,

 

I usually get this question about basic angles.  For example, if I use 3X 120 degrees, does the 3X go into the box, or just the 120 degrees.  The answer is either.  The Y14.5 standard shows examples of both.  As a personal preference, I usually leave the 3X outside of the box and just put the dimension inside.  But, since both are legal, I'm not consistent with that preference.

 

The answer is the same for dimensions other than angles.  And, as you mentioned, if the surfaces are coplanar and lines are extended from one surface to another (to show they are not offset), it is unnecessary to even include the number of surfaces.  Redundancies such as stating the number of surfaces, even when it is evident, aren't forbidden or even frowned on by ASME standards.  Clarity is the key goal for all drawings and whatever you can do to make the drawing the most easily interpretable is usually the best practice.

 

Labeling datum features that include multiple coplanar or coaxial surfaces or giving geometric tolerances to multiple surfaces such as these (as in assigning profile to control coplanar surfaces or runout to control coaxial surfaces) can be confusing unless the number of surfaces is stated or multiple leader lines are used.

 

I used to conduct training at the Berkeley Space and Science Labs years ago.  It was always interesting work and great people to work with.

 

Jim



 

Subject: GD & T Question on Composite Position Tolerancing


Jim,

I was a student at one of the GD&T classes you teach at UW-Milwaukee.  I attended about a year ago.  An interpretation of a customer print has come up which has all of us at MKC discussing.  If you would be so kind to give us your interpretation, it would be greatly appreciated.


We have a situation where composite position tolerancing is being used.  The upper true position segment is not in question.  The lower position, being a more restrictive tolerance, refers to datum -A- only which includes perpendicularity of two holes to datum -A-.  Are the two holes in question considered a pattern when their basic dimensions are only independently dimensioned from datums -B- and -C- with no basic between them?

The question is: There is no datum reference in this frame from datums -B- and -C-; and since the two holes are defined independently from datums -B- and -C-; do they remain unlocked or is a basic implied resulting in a pattern requirement for perpendicularity and position to each other?

  
Jim, we know the intent of the design which is a pattern.  We just want to confirm the GD&T does not convey the intent.


Thanks.
Gary

 

 

Gary,

 

As long as a basic dimension is calculable between the holes within the pattern from the other basic dimensions on the drawing, the drawing is correct and the lower segment of the composite position control with the tighter tolerance applies to the distance between the holes.

 

Hope this helps.

Jim

 

Subject: Question Regarding Showing Inches and Millimeters on the Same Drawing

 

Jim,

Long time no talk.

Iím a former student of yours at 3M.  I have a question about tolerancing on a
print that I can't find the answer in any of my books.

When English and Metric tolerances are listed, is there a correct method
for doing so?

Example:  
d .033 Ī .002 (0.84 Ī 0.05)

For each dimension, we put the metric dimension in (Parenthesis) and sometimes [Brackets].  Is this OK?

Also, do we need to repeat the Diameter sign in the metric callout?  Redundant?  And to get picky, is there a spacing procedure as in between the diameter sign and the size?

These are some questions I'm getting. If you could shed some light on this one way or another, I would appreciate it.

PS.  Is ASME Y14.5M-1994 still the current standard?

Thanks for your help.

Regards,
Paul

 

Paul,

 

In prior versions of the Y14.5 standard, they showed methods, like the one you list, to allow both inches and millimeters on the same feature.  Even though the one not shown in brackets took precedence, there were legal problems with companies meeting one of the tolerances, but not the other (since, with rounding, both numbers were not exactly equivalent).  So, in recent versions of the standards, this practice is not shown.

 

As far as the rules, if you decide to do it anyway, the second number would be assumed to have the same shape tolerance zone as the first, so repeating the diameter sign is not necessary.

 

Since these practices have not been allowed per Y14.5 since prior to 1982, I've attached a couple of illustrations of how they looked when they were allowed from a very old Y14.5 standard.

 

Yes, ASME Y14.5M-1994 is the current dimensioning and tolerancing standard.  There are other more recent standards that augment that standard though, like ASME Y14.41-2003 Digital Modeling Definition Data Practices and ASME Y14.43-2003 Dimensioning and Tolerancing Practices for Gages and Fixtures.

 

Hope this helps.

Jim 

 

Illustration from ANSI Y14.5M-1982, Appendix D Former Practices

 

Illustration from ANSI Y14.5M-1982, Appendix D Former Practices

 

 

 

Subject: Question on Assigning Datum Feature Symbols

 

Jim,

Another question for you if you have time.

 

About datum selection: We have a pattern of holes on a plastic connector. It is not critical to the outside of the part. Can I use the pattern centerlines in each direction as the datums? Legally to ASME Y14.5M-1994, some say it is not a feature size, so I can't. See attached sketch for more info. (See attached file: Datums.doc)


Thanks for your help.  Please reply to all with your response.  Other 3M'ers need this info as I might be away.



Regards,
Paul

 

 

 

 
 

Paul,

 

No, that's not legal.  As the others have said, it isn't a feature of size.  However, you can use one, two or all of the rectangular hole widths as a single datum feature (one) or a datum feature pattern (more than one).  In my yellow textbook, on page 148, I show an example of rectangular hole widths being used to construct a datum reference frame.  There are also examples of pattern datums being used on page 488.

 

 

Hope this helps.

Jim

 

Illustration from yellow textbook page 148 below:

 

Illustration from yellow textbook page 488 below:

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