Sr GDTP Y14.5-2009 Exam Review Ch-1 Sep 2021

[metrologic]

Sr GDTP Y14.5-2009 Exam Review Ch-1 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 by taking the higher level exam. Maybe some forum members could quiz me on chapter 1???


Also, there's a couple things in this chapter I'm kinda worried about.
Q1. Could someone elaborate on 1.4 Fundamental Rule o: "Dimensions and tolerances apply only at the drawing level where they are specified.? Seems like a lot of paper has to be pushed if specs don't carry up from detail drawings to assembly drawings.

Q2. 1.6.4 Conversion and Rounding of Linear Units. I don't have access to the referenced document. Do you think there is something in there that would be on the exam? I'm assuming conversions between IN and mm are exact, but how would rounding play into this?

Q3. 1.8.1 Diameters. "Where... a number of concentric cylindrical features are specified, such diameters should be dimensioned in a longitudinal view if practical." Is the longitudinal view looking down the barrel? Or section the barrel and create a side view?

 

[3DDave]

A1: This is usually not the problem it seems. The parts of an assembly need to have passed inspection and it's assumed no one is bashing them with a hammer or doing other damage after inspection. If one wants, any part at any time can be reinspected in accordance with the individual part drawing.

However, if one were to depend on a feature of a part to use as a datum feature in a higher assembly, then the characteristics that qualify that feature need to be called out at the assembly level rather than requiring the assembler to have to go get the detailed part print. It's to prevent the need for a cascade of paper to discover assembly level requirements that might otherwise require a significant investigation of component parts.

A2: conversions are only exact if a sufficient number of places are allowed. 0.01mm = = 0.0003937007874015748 inches. One significant figure would convert that to 0.0004, an inexact result.


A3: longitude => late Middle English (also denoting length and tallness): from Latin longitudo, from longus ‘long’.

 

[metrologic]

Thanks for responding 3DDave. If an IN unit drawing had to be converted over to mm units, does one round? Or is rounding only used when going from mm to inches? And is there some higher logic that dictates whether to round up or down? I mean, are we trying to ensure the design limits in the original units are not exceeded, or is there some other consideration?

 

[3DDave]

https://www.govinfo.gov/content/pkg...VPUB-C13-f10c2ff9e7af2091314396a2d53213e4.pdf

has some guidance (section 4.4), but buying that spec is the only way to be sure.

 

[Woosang]

metrologic,

A2: Good to know how it works, but what is not elaborated in Y14.5 may not be on the exam.

A3: A view similar to Fig 2-4, with diameter dimensions.

 

[metrologic]

@Woosang

Yeah, when I took the tech level exam a few years ago, I can't recall there being anything that wasn't directly addressed in Y14.5, but my memory is kinda fuzzy.

 

[metrologic]

Two more questions on chapter 1 and then I think I'm good.

Q4. 1.3.54 Actual Local Size. "the measured value of any individual distance at any cross section of a feature of size." This is a pretty vague definition if you ask me. Is this all we get? They do a better job defining a derived median plane and derived median line.(1.3.30) With the derived medians, the inspection method is described a bit more, where the cross sections are required to be perpendicular to the actual unrelated mating envelope.

Q5. 1.7.9 Dimensions Not to Scale. (a)"Where the sole authority for the product definition is a hard-copy original drawing... ...and it is not feasible to update the pictorial view of the feature, the defining dimension is to be underlined with a straight thick line." What is the significance of "sole authority"? What if it's not? --then what, underline it twice?? Why did ASME put "sole authority" in that sentence?

 

[3DDave]

A5: No one knows all of why the Y14.5 Committee does anything; like most committees they can get all the worst dynamics of group-think possible and put them into writing.

I'm with you - that makes no sense.

One area that causes problems with that Committee is they often deal with some combination of factors, in this case paper drawing and computer representation; there are 3 combinations, but they deal with only 2, leaving the remaining one ambiguous.

If they are implying that a CAD file of the part would over-ride that then they should have explicitly stated that that dimension should be reference on the drawing and the view identified "NOT TO SCALE." But, I'm not part of that group.

Here's a mind-bender. How to-scale must a feature on a drawing be? If the feature has a tolerance on a dimension of +/- 0.001 is the view out of scale if the line depicting that feature is fatter than that? In addition, the first rule of using drawings is to never measure from the drawing unless the drawing is a Stable Base drawing.

I expect questions on this topic are of the Parrot type - that is, regurgitating or recognizing the exact verbiage in the standard with no need to interpret, understand, or draw any conclusions.

 

[metrologic]

@3DDave
"I expect questions on this topic are of the Parrot type..." Yeah, I recall the tech level exam had a few like that. I'd run into a question where I just couldn't recall the context of the specific verbiage used. Those are the ones I struggled with. I spent too much time reading various GD&T study books, and not enough reviewing the actual language of the ASME Y14.5 standard.

 

[metrologic]

A couple questions regarding features of size came up at work last week.

Q6. 1.3.32.1 Regular Feature of Size. They include "...a set of two opposed parallel elements or opposed parallel surfaces, each of which is associated with a directly toleranced dimension." As an example, would two parallel elements on opposite sides of a drafted slot be "opposed parallel elements"? Or is it required that the surface normals point back at the element on the opposite side? Could one directly tolerance a pair of elements on a drafted slot as a regular feature of size?

Q7. 1.3.32.2 Irregular Feature of Size. Paragraph (b) "a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope other than a sphere, cylinder, or pair of parallel planes" Is there a good canonical example of this type that a can use for a picture in my head?