Effective Training Inc. Message Board

We have a part that has four 17.91±0.06 interrupted diameters along a shaft as shown in the picture.

The supplier has been considering these as four separate features. The customer says these four features should be considered and measured as one feature. I was interpreting this drawing as the supplier with the four features being separated because of the "(4X)" in front of the 17.91 call-out. The twist is that the drawing indicates "Dimensioning and Tolerancing in accordance with ISO 8015, General Tolerances: ISO 2768-mK". I was told that ISO standard dictates that these four features be considered as one but I cannot verify this as I am not well versed in the ISO 8015 standard.

Does anyone know which is the correct interpretation? Would the interpretation for the concentricity be different than for the FOS requirement? Is there a better way to dimension this in the ISO standard?

Thank you for any assistance in advance.

_________________
Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems

*BUMP*

I still haven't found a definite answer on this. I still think from everything I have read so far that they should be considered 4 separate elements.

I also cannot find how this would be dimensioned if they were to be considered one feature.

Will post answer here if I find it.

Thanks in advance for any support on this.

_________________
Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems

AWeaver,

I agree that the use of the typical "4X" suggests that this is four separate features. Each individual feature would have the geometric control applied independently. I think this confusion is what lead the ASME Y14.5 committee to add a NEW GD&T modifying symbol to the 2009 standard... the "Continuous Feature" symbol, the letters "CF" surrounded by a hexagon. Not sure if the ISO standard a similar control but perhaps they do. I have seen some ASME Y14.5M-1994 drawings that actually have the words "Continuous Feature" under the controls for an interrupted diameter.

Perhaps someone knows how the ISO standard handles this!

I wish this print was using ASME. Then I would have more confidence to know what the correct interpretation is.

I am awaiting my ISO standard but need to waddle through the red tape in these time of financial prudence

Thanks for your feedback

_________________
Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems

Hi Guys,

A great discussion you two have going. First, I want to give a plug for Alex's new “ISO Geometrical Tolerancing Reference Guide” that will be published soon. It will be the most exhaustive coverage of the ISO standards with lots of great examples to help you understand the standards. It will answer all of your ISO questions.

I must first preface my answer with the statement that my answer is dependent on the information provided in your question. Several factors that could affect my answer are:

1. The drawing release date, this affects which version of the ISO standard applies. ISO 8015 was revised in 1985, and ISO 2768 was revised in 1989.
2. Additional standards referenced on the drawing, such as ISO 1101. This standard was revised in 2004. The drawing should reference this standard also and its revision date to avoid any confusion.
3. The standards listed above also reference other ISO standards that affect drawing interpretation. There are approximately 20 other ISO standards invoked by the three standards mentioned above.

Nothing in these three ISO standards, or their related standards, states that we should interpret the four diameters as one. The “4x” in front of the size dimensions means there are four diameters with the same nominal size and tolerance. You must inspect each diameter separately for size. Therefore, you will have four separate size measurements shown in your inspection report.

The coaxiality tolerance applied to the size dimensions means there is a cylindrical tolerance zone of diameter 0.1 centered about the A-B datum axis. Whether you interpret coaxiality as a single tolerance zone for all four diameters or as four separate tolerance zones does not affect how coaxiality is measured. This is because ISO 1001:2004 states that coaxiality applies to the extracted actual median line. This is an imperfect line (not straight) passing through all the median (center) points of each cross section. Therefore, practically speaking, the center points of each cross section must be in the tolerance zone. You will have to measure at least four cross sections to know if the center points of each diameter lies in the tolerance zone. If the diameters were longer, you would need several cross sections for each one.

Interpreting the four diameters as one would only affect the measurement report. If interpreted as one diameter, the measurement report could show coaxiality only once. This is not a good practice because if a part failed coaxiality and you reported it just once, you would not know where it is out. By reporting coaxiality four times, if three diameters were good and one was out, you will know which one failed.

If the drawing referenced ASME Y14.5-2009 and used the CF modifier, then the four diameters become one feature of size. This is significant because Rule #1 (envelope principle) would apply to the full length of the four diameters. This means the size tolerance controls the straightness of the axis established by all four diameters for their full length. There is no equivalent symbol in ISO. Even if ISO had an equivalent symbol, the envelope principle would not apply because ISO 8015 invokes the independency principle. This means that the size and form are independent. Size is only a two-point measurement at each cross section. This means the straightness tolerance may exceed the size tolerance and the drawing must specify the straightness tolerance. To invoke the envelope principle in ISO, an encircled “E” symbol is placed next to the size dimension or a capital letter “E” suffix is shown after ISO 2768, (i.e. ISO 2768:1989-mK-E). However, the envelope principle will apply individually to each diameter.

Referencing ASME Y14.5-2009 and using the CF symbol also affects how coaxiality is measured. With the CF symbol, the axis of the actual mating envelope established by all four diameters must lie in the tolerance zone. Without the CF symbol, the axis of the actual mating envelope of each individual diameter must be in the tolerance zone. If the diameters were significantly off center and skewed and two diameters were diametrically opposite the other two, then the individual axes may fail, but the one axis established from all four may pass.

There is a CZ (Common Zone) symbol in ISO used with geometric tolerances applied to multiple surfaces when you want all the surfaces to be in one common zone. ISO 1101 shows it placed inside a flatness tolerance frame applied to multiple co-planar surfaces. It is equivalent to profile of a surface applied to multiple co-planar surfaces in the ASME standard. However, using CZ with coaxiality will not affect the interpretation either because, as stated above, whether you have one zone or four the measurement is the same per ISO.

If you invoke the envelope principle in ISO and specify a zero straightness tolerance at MMC (MMR in ISO) with the CZ modifier on the “4x” diameters, then you will have an interpretation similar to ASME with the CF symbol applied to the size dimension and Rule#1. However, this will only control the straightness of the four diameters within one tolerance zone, but still does not affect the measurement of the coaxiality tolerance.

I hope this is helpful. Check our website often, so you will know when Alex’s new ISO reference guide is available. If you need further assistance with this, feel free to contact us directly.

_________________
Best Regards,
Roy Cross
ASME GDTP Senior Level S-0488
Dimensional Engineering Mentor
Effective Training, Inc.
2118 S. Wayne Rd.
Westland, MI. 48186
royc@etinews.com
http://www.etinews.com

Roy,

Thanks for the reply. Your knowledge to navigate the dimensioning standards and ability to articulate dimensioning concepts still amazes me as it first did when you taught my GD&T fundamentals class.

Your response clarifies this situation for me and confirms my first analysis of this situation

I am in the process of acquiring the ISO standards, but I will also check out Alex's new publication when it is available.

Thanks again!

_________________
Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems