Sr GDTP Y14.5-2009 Exam Review Ch-3 Sep 2021

[metrologic]

Sr GDTP Y14.5-2009 Exam Review Ch-3 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. I'm up to chapter 3! There's a couple questions I have.

Q1. 3.3.24 Independency Symbol. "This symbol indicates that perfect form of a feature of size at MMC or LMC is not required." By default, perfect form at LMC does not apply already. When would this symbol be used to indicate perfect form at LMC is not required?

Q2. 3.3.27 Movable Datum Target Symbol. See Fig 3-22. Does the symbol always point straight left or right? Or should it point in the direction of movement? Or does the line connecting the symbol to the target point indicate the direction of movement?

On to chapter 4!

 

[greenimi]

Q1: Perfect form at LMC is applicable when you have a callout modified at LMC and consequently PF at MMC is no longer applicable.
Q2. Yes. Always right or left in ASME and direction of movement in ISO

 

[metrologic]

Thanks greenimi.

Regarding Q1: If independency is indicated, wouldn't a from control be required? And once the form control is indicated, doesn't that make the independency symbol redundant? I suppose the form control could be indirectly applied, like in Fig 2-7 where a flatness tolerance is used to control only the upper side of a feature of size. That use case makes sense to me.

 

[3DDave]

(I) is to indicate that the drawing creator intended to have a form tolerance that exceeds the limits of the size constraint and did not make an error. Yes, the standard indicates that without a form tolerance on an (I) feature of size, that the form is uncontrolled.

 

[SeasonLee]

Regarding Q1: If independency is indicated, wouldn't a from control be required?

Please note the highlighted caution for 2009 version

Same caution on 2018 version but "independency" added, I think its better than 2009 standard.

Season

 

[pmarc]

There is one more subtle, but quite significant, difference between the two caution notes. It is lack of "entirely" in the 2018 version. I assume it's because they realized that with the swept sphere interpretation of limits of size, as defined in Y14.5.1, (I) is simply not able to entirely cancel out form control of cylindrical features of size. I am pretty sure that this is also the reason why figs. 2-7 (in 2009) and 5-10 (in 2018) does not show a cylinder but a slab.

Note: This kind of knowledge will definitely NOT be required to pass the Senior level exam.

 

[metrologic]

@pmarc
Interesting. I haven't looked at Y14.5.1M in a long time. At some point after the exam I will circle back and examine the definitions in there again.