Middle plane orientation
Middle plane orientation
(OP)
Will the orientation of the side faces of a cube to the bottom feature control the orientation of the middle plane to the bottom feature
ASME Y14.5-2009
Picture a parallelepiped / cube (regular feature of size):
If two side faces (both) are perpendicular to the bottom face within some tolerance (let’s say .005 and .008 respectively---from the raw material), the width (the distance between them) is controlled by a size tolerance (let’s say .012—also from raw material), then the question is what is maximum perpendicularity error allowed between the middle plane and the bottom surface. The part has datum feature A = bottom face and datum feature B, secondary = the .012 width, oriented within some amount (the one I am trying to get the maximum value) to primary datum feature A
If picture is needed, please let me know.
ASME Y14.5-2009
Picture a parallelepiped / cube (regular feature of size):
If two side faces (both) are perpendicular to the bottom face within some tolerance (let’s say .005 and .008 respectively---from the raw material), the width (the distance between them) is controlled by a size tolerance (let’s say .012—also from raw material), then the question is what is maximum perpendicularity error allowed between the middle plane and the bottom surface. The part has datum feature A = bottom face and datum feature B, secondary = the .012 width, oriented within some amount (the one I am trying to get the maximum value) to primary datum feature A
If picture is needed, please let me know.





RE: Middle plane orientation
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Middle plane orientation
Green face perpendicular within .005 to red.
Yellow face perpendicular within .008 to red
Green to yellow within .012
Plane 1, datum feature aligned with the size dimension.
Plane 1 to red orientation within???
RE: Middle plane orientation
I am curious myself, why the "maximum perpendicularity error allowed" (as requested) cannot be mathematically calculated?
What could be the worst case?
RE: Middle plane orientation
Within that tolerance zone the surface can take any form and shape imaginable.
How to pick "worst case" out of infinite number of possibilities?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Middle plane orientation
Based on the configuration shown, do you really think that the perpendicularity of the middle plane (datum B, driven from the two side faces) to the bottom face (datum feature A) can be any amount? In other words, it is not limited to anything?
Just curious.
RE: Middle plane orientation
Either way it will be limited to something you specify on the drawing.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Middle plane orientation
A= the bottom face
B= the middle plane (RFS)
The part is assembled (with its mating components) based on datum feature A primary and datum feature B secondary (RFS) . The coordinate system for this part is A primary and B secondary (DRF: A and B)
When the part is defined on the drawing: A become primary and B - (as a secondary datum feature secondary) - should be oriented to A, correct?
The appropriate callout would be perpendicularity within some amount (functionally amount ) to A (primary).
Let’s pretend, for a second, that the functional amount for perpendicularity between primary A and secondary B is determined. Known number (let’s say came from research and development)
The question is: if the functional amount is bigger than the “calculated” one (the one limited by the two perpendicularities to the bottom face and maybe the size requirements/ width) then the perpendicularity of B to A is useless.
Am I correct? Or am I missing something?
Are you going to add it on the drawing or rely on the “calculated” amount (since this amount is more restrictive anyway). Probably, the OP question (and my question too) is what is that amount = that point of diminishing returns.
RE: Middle plane orientation
Certified Sr. GD&T Professional
RE: Middle plane orientation
mkcski,
For the perpendicularity callout applied to a width FOS, the callout controls orientation of unrelated actual mating envelope of the FOS (UAME), not RAME. RAME, by definition, is perfectly related (oriented) to applicable datum(s) - datum plane A in this case - thus has 0 perpendicularity error to datum plane A. Center plane of RAME is nothing but the datum plane B in this case.
RE: Middle plane orientation
If for you is too complex.............can you imagine what is for me.
RE: Middle plane orientation
RE: Middle plane orientation
You were the first to use the word "mathematical"
Unfortunately, even when things look simple on the surface, establish solid mathematical proof that will satisfy infinite number of possibilities, may not be a trivial task.
That's why I keep saying over and over again: if you see something is unclear or ambiguous just apply appropriate control directly to it. Don't expect everybody out there to appreciate highly sophisticated but confusing approach.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Middle plane orientation
Your ability to communicate GDT in words is far superior to mine. Until I recently found this forum, I did very little written communication wiht GDT. I was trying to say what you so clearly described. Please excuse any confusion I may have caused others.
Certified Sr. GD&T Professional