Parallelism Does not Control Form? Question for GD&T Certification Practice Exam

[armand_matossian]

Here's a test question:

The 0.1 parallelism control will:

a. limit the flatness of the surface to 0.1

b. override Rule 1

c. not control the flatness of the surface

d. increase the outer boundary to 20.7

**(This question is referring to a simple plate. Datum A is the base of the plate and parallelism is applied to the top of the plate)

__________________________________________________ ___

The correct answer is (c). However, can someone please explain how the answer is not (a)?

I understand that parallelism is technically not categorized as a "form" control. However, if the surface deviation was to exceed 0.1, then wouldn't that also cause the parallelism to also exceed 0.1? So that, yes this parallelism is controlling the flatness to 0.1.

If (a.) is an incorrect answer, then does that imply that the flatness can exceed 0.1 but still be parallel within 0.1?

Someone please explain

[Kelly_Bramble]

Which dimensioning and tolerancing standard?

ASME and ISO have different interpretations based on Rule #1 and the Envelope Requirements clauses.

Also, is the parallelism applied to a surface or feature of size?

[armand_matossian]

This is for ASME Y14.5M.2.

It turns out that in the question I was referring to there was actually a tangent modified to the top surface that I missed.

[Kelly_Bramble]

There is no ASME Y14.5M.2 document or other - you're probable using one of the following

ANSI Y14.5M-1973
ANSI Y14.5M-1982
ASME Y14.5M-1994
ASME Y14.5-2009
ASME Y14.5-2018

You should determine the standard and identify it when asking questions..

It matters

[spektre76]

Profile of a Surface would solve all of this. It controls: SIZE, PERPENDICULARITY, FORM, ANGULARITY.