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Sr GDTP Y14.5-2009 Exam Review Ch-2 Sep 2021

Sr GDTP Y14.5-2009 Exam Review Ch-2 Sep 2021

Sr GDTP Y14.5-2009 Exam Review Ch-2 Sep 2021

Sr GDTP Y14.5-2009 Exam Review Ch-2 Sep 2021

Hi Everyone! I'm studying for my Senior GDTP Y14.5-2009 Cert Exam. I currently hold the tech level, but would like to refresh my knowledge of this subject matter through re-certification. There's a few questions from chapter 2 that I would appreciate your help with.

Q1. Implied 90 degree Angle. Why is there only an implied 90 degree angle dimension and not also an implied 0 degree angle? This is in contrast to the next paragraph (; "Where center lines and surfaces are depicted ... intersecting at right angles or parallel to each other and basic dimensions or geometric tolerances have been specified, implied 90 or 0 degree basic angles are understood to apply." Is this related to Fig 2-5 where two parallel but unopposed planes are dimensioned and toleranced?

Q2. 2.3.1 Millimeter Tolerances. In paragraph (c): "Where limit dimensioning is used and either the maximum or minimum value has digits following a decimal point, the other value has zeros added for uniformity." Is this true even when one of the limits is zero?

Q3. 2.3.2 Inch Tolerances. This is more of a complaint. Why is there "no requirement for the (IN) basic dimension value to be expressed with the same number of decimal places as the tolerance." I fee like this unnecessarily breaks from the pattern established in 1.6.2. In contrast, a millimeter basic "observes the practices of para. 1.6.1."

Q4. 2.3.3 Angle Tolerances. Another complaint. Decimal angle tolerances use a preceding 0 before the decimal point, the same as millimeter linears. But the associated decimal angle dimensions must be expressed to the same number of digits past the point as their tolerance, as is done with inch dimensions. This seems needlessly complicated -particularly since non-decimal angle dimensions are not padded with zero degrees or seconds to match their tolerance.

Q5. 2.6.1 Dimensional Limits Related to an Origin. The example shown in Fig 2-5 illustrates an application of the origin symbol. Two parallel but unopposed surfaces are shown at 12mm +/-0.4mm apart. Since they are not opposed they can't be a feature of size. The origin symbol establishes the high points of one surface as an origin for a tolerance zone to control the other surface. What happens if the origin symbol were used on a set of parallel surfaces that are opposed? Would this be a regular feature of size? Would all local sizes be controlled and would perfect form at MMC be required?

Q6. 2.7 Limits of Size. "Unless otherwise specified, the limits of size of a feature prescribe the extent within which variations of geometric form, as well as size, are allowed. This control applies solely to individual regular features of size...." Could this be expanded to include irregular features of size in some manner? Why can't this include irregular features of size?

Q7. 2.7.1 Variations of Form. Paragraph (d) states: "In cases where a geometric tolerance is specified to apply at LMC, perfect form at LMC is required." Okay, so we are talking about features of size, and paragraph (d) says applying an LMC modified geometric tolerance will trigger a perfect form at LMC requirement. Is it possible to apply an LMC geometric tolerance and an MMC geometric tolerance to the same feature? Would that establish boundaries of perfect form at both LCM and MMC?

Q8. 2.7.4 Relationship Between Individual Features. "The limits of size do not control the orientation or location relationship between individual features.... These tolerances may be specified by one of the methods given in Sections 6 through 9." Is the rest of this subsection redundant? It goes on to say: "If it is necessary to establish a boundary of perfect form at MMC to control the relationship between features, one of the following methods may be used:..." And then appears to describe the same controls presented in Sections 6 through 9. Am I missing something here?

Q9. 2.8 Applicability of Modifiers on Geometric Tolerance Values and Datum Feature References. "RFS, MMC, and LMC may be applied to geometric tolerance values on features of size. RMB, MMB, and LMB may be applied to datum feature references." The text doesn't specify regular or irregular features. Earlier in 2.7 the standard indicated that geometric form controlled by the limits of size "...applies solely to individual regular features of size...." Can MMC, MMB, LMC, and LMB be used with irregular features of size? Do irregular features of size have defined maximum and least material conditions or associated perfect form boundaries that could be triggered by a modifier?

Q10. 2.8.2 Effect of MMC. "Where a geometric tolerance is applied on an MMC basis, the allowed tolerance is dependent on the size of the unrelated actual mating envelope (UAME) of the considered feature when considering effects based on the axis interpretation." Which geometric characteristics are we talking about here? Does it include form? -a form tolerance isn't based on the UAME is it? In the very next subsection (2.8.3 Effect of Zero Tolerance at MMC), only position and orientation are mentioned: "Where a tolerance of position or orientation is applied on a zero tolerance at MMC basis, the tolerance is totally dependent on the size of the unrelated actual mating envelope of the considered feature."

Q11. 2.14 Flat Tapers. "A flat taper may be specified by a toleranced slope and a toleranced height at one end. See Fig. 2-20." What is the tolerance for the basic slope in Fig 2-20? Don't we need a couple of origin symbols in there somehow to make all the tolerances fully defined? In contrast, look at Fig 2-18 where tolerancing an angular surface is described. In that example two origin symbols were used and I think that really helps clear up any possible confusion about interpretation.

RE: Sr GDTP Y14.5-2009 Exam Review Ch-2 Sep 2021

In order to get some answers I think you should split the questions in separate threads. My opinion

RE: Sr GDTP Y14.5-2009 Exam Review Ch-2 Sep 2021

I appreciate your support greenimi. Yeah, maybe separate threads would attract more responses -there would be *a lot* of threads though. What do you think of Q5? Once the first response comes in I bet there will be a flood more. I feel like Y14.5 is a foundational standard, it's really interesting to discuss.

RE: Sr GDTP Y14.5-2009 Exam Review Ch-2 Sep 2021


These questions would be interesting to discuss, but I'm not sure that this will help you to prepare for the GDTP exam. From what I remember about the Y14.5M-1994 Senior level exam in 2004, it was very much about remembering what it says in the standard. Not how to apply it, not what it means at a deeper level, not how to extend the concepts to apply in different situations.

Q5 is a good example. According to Section 2.6.1 and Figure 2-5, the Dimension Origin tool creates something very similar to a Profile of a Surface tolerance of 0.8 on the upper surface, with the lower surface referenced as a datum feature. If Dimension Origin was applied to a feature with opposed parallel planes as you suggest, what controls would apply? That's a good question, and I've actually never thought about that particular situation before (possibly because I've seldom seen Dimension Origin actually specified on a drawing). The Dimension Origin requirement is very different from the local size and Rule #1 requirements, and it's easy to imagine actual part configurations that would pass one and fail the other. We can speculate on what we think would (or should) apply, but nobody really knows and Y14.5 doesn't go there. I don't think that the GDTP exam will ask that type of question.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

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