Sr GDTP Y14.5-2009 Exam Review Ch-6 Sep2021

[metrologic]

Sr GDTP Y14.5-2009 Exam Review Ch-6 Sep2021

Hi Everyone! I'm up to section 6, Tolerances of Orientation. As you may recall, I'm working through the Y14.5 standard in preparation for upgrading my GDTP certification from the tech level to the senior level. Here are some questions I had on this section:


Q1. 6.4.3 Tolerance Zones. "Although orientation tolerances are only constrained in rotational degrees of freedom relative to the referenced datums, the notation of EACH RADIAL ELEMENT adds a requirement for the tolerance zone(s) to be constrained in location relative to the axis from which the radial elements emanate." The rules for checking controls with EACH ELEMENT always seem rather ad-hoc or poorly defined. They seem to break the overall pattern of Y14.5.

Q2. Fig. 6-16 Specifying Perpendicularity for a Radial Element of a Surface. Does the perpendicularity control in this figure apply to what appears to be the bevel at the base of the datum A cylinder? Or does the control refer to only the surface seen on edge that is directly in contact with the leader arrow head?

 

[Burunduk]

Q1 doesn't seem like a question. I agree with the point, though.

Q2 is actually a good question because the considered surface looks like it's supposed to be nominally perpendicular to datum axis A only at one radial cross-section (out of infinite). So in this case "EACH RADIAL ELEMENT" note looks inappropriate, unless I'm missing something.

I wonder what the others think regarding Q2.

Edit:
By the way, EACH RADIAL ELEMENT concept and this figure were dropped from the orientation section in the 2018 edition of the standard.  

Subparagraph 9.3.3 in the new version of the standard states:

"Adding a notation such as “EACH RADIAL ELEMENT” invokes a translational degree of freedom that cannot
be controlled by orientation tolerances. When control of radial elements is required, profile shall be used.
See subsection 11.9."

 

[pmarc]

Regarding the rules for application of EACH ELEMENT or EACH RADIAL ELEMENT in the standard (both versions, 2009 and 2018), the whole logic the committee developed should also lead them to a conclusion that for the straightness tolerance of line elements of a cylinder, a datum self-reference is needed in the straightness FCF because the planes in which the individual straightness tolerance zones are must pass through the UAME axis of the cylinder, that is, through the datum axis established from the cylinder.

Or if they wanted to be consistent throughout the standard, for the line straightness tolerance applied to a flat surface, they should put a similar statement to the one from para. 9.3.3 in the 2018: "Applying straightness tolerance to line elements of a flat surface invokes an orientational degree of freedom that cannot be controlled by form tolerances. In such cases, profile of a line shall be used."

;-)

But seriously speaking, this is something that Y14.5, as opposed to ISO GPS, has never developed solid rules and tools for. I hope things will change in a future as Y14.48 standard for universal direction and load indicators gets published.

 

[Burunduk]

pmarc,
My opinion regarding EACH ELEMENT and EACH RADIAL ELEMENT is:
There's nothing catastrophic about "EACH ELEMENT" except for the well-known drawing-view dependency problem when no secondary datum is used; most users who apply/interpret the concept regulary are probably somehow accommodated to it. However, "EACH RADIAL ELEMENT" for orientation is more problematic, since it creates a possible location constraint of the entire feature to the axis. I say that wether this creates a problem or not depends on the type of nominal feature geometry and what kind of relationship it may have with the axis that defines "RADIAL". For example, If the considered surface is nominally normal to the datum axis - not a problem, since no translational DOF are constrained by the datum reference for the feature being controlled for perpendicularity of radial elements. However, If the feature is conical, and you are controlling angularity of line elements - that's a whole different story, and that is what I assume the committee was concerened about when they decided to drop EACH RADIAL ELEMENT, but not EACH ELEMENT, from the specification in the orientation section. But, I believe you know better, so let me know if I'm on track here... 

 

[pmarc]

Burunduk,

To be honest, I don't know why the committee decided to do what they did with the EACH RADIAL ELEMENT in the 2018. My opinion, after reading the subparagraph in 9.3.3, has always been that the decision was made based on an incorrect premise, because the notation EACH RADIAL ELEMENT does not, in fact, constrain translational degrees of freedom of the individual 2D orientation tolerance zones (pairs of two parallel lines) - it is used to indicate that each individual plane containing the 2D orientation tolerance zone shall pass through the datum axis. These are two different concepts that should have never been mixed together.

 

[metrologic]

What is Y14.48?

 

[Burunduk]

it is used to indicate that each individual plane containing the 2D orientation tolerance zone shall pass through the datum axis

If the control was applied to a cone, and the datum was a cylinder axis, wouldn't the collective effect of the 2D tolerance zones passing through the datum axis control the centering location of the conical surface to the datum axis?

 

[3DDave]

The ASME Y14 48 subcommittee is working on a standard. There is no 14.48 standard available. See

https://cstools.asme.org/csconnect/...le=52074.pdf&dir=CommitteeFiles&44581.0759954

for details.

 

[pmarc]

If the control was applied to a cone, and the datum was a cylinder axis, wouldn't the collective effect of the 2D tolerance zones passing through the datum axis control the centering location of the conical surface to the datum axis?

Maybe it would, but I doubt the committee was thinking about it the same way you do. What probably did not fit to their general logic for orientation tolerances was the fact that the 2D tolerance zones for each radial element needed to pass through the datum axis and this implied locational relationship to them.

From what I know, one of the reasons for formation of Y14.48 subcommittee was to address this problem. Actually, the document that 3DDave just linked to mentions about the ambiguity (lack of rigorous and repeatable requirements) of the legacy and view-dependent methods. It also says that ISO 1101 was used as basis for the development of Y14.48.

Overall, the whole topic of line element controls has been a gray area in Y14.5 and point of contention for many years. For the GDTP certification, this definitely is not the level of detail that will be examined.