are these these geometrically the same?
are these these geometrically the same?
(OP)
One example uses parallelism and perpendicularity while the other uses profile. I'm sure they are inspected differently but are they geometrically the same thing?
Thanks in advance,
Greg
Thanks in advance,
Greg





RE: are these these geometrically the same?
Thanks
RE: are these these geometrically the same?
My initial post did not have datum B for the profiled rectangle, however I find it locks only 3 degrees of freedom where the other rectangle locks 5 degrees of freedom.
Hopefully that made sense.
RE: are these these geometrically the same?
RE: are these these geometrically the same?
RE: are these these geometrically the same?
At first glance: you cannot use BSC dimensions with parallelism and perpendicularity to control the size of the block. So your comparison question is somewhat moot.
The relationship between Datum A and the top face is not parallelism but is perpendicularity. So the control is not per Standard. From a drafting standpoint, the controls only apply in the view shown. So you should apply the control in the end view. You have taken a reasonable liberty in showing the "perpendicularity" relationship by identifying Datum in the front view. But I assume be block is "square" so other views maybe needed to confirm my assumption.
In the profile example, Datum B is included in the profile tolerance. Although technically possible ,it is not good practice to have a feature related to itself.
Certified Sr. GD&T Professional
RE: are these these geometrically the same?
You're right, basic dimensions cannot be used for parallelism and perpendicularity (smacks forehead). That answers that question then. You're statement about the profile example leads me to another question. Let's say I want the profile "window" of .030 around the part, but I want the part to be inspected where the part is "laying" on datum A and "clocked" by datum B. In the attached picture I drew the .030 window (actually .15 but made it bigger for clarity) and the profile of the actual part. If I "clock" this part so feature B is horizontal then the bottom edge will fall outside of the window and will fail inspection (which is what I want). This was my reasoning for adding datum B to the profile FCC. Is this appropriate or is there a better way of doing this? Still trying to get my head around this stuff.
RE: are these these geometrically the same?
Datum B clocking is not needed. The all-around symbol implies a BSC 90-degree rectangular relationship between the four surfaces, so clocking is not necessary. See 2009 Section 1.4, paragraph (j) By adding Datum the 4 surfaces collectively (as a group) are to be perpendicular to the datum feature.
Certified Sr. GD&T Professional
RE: are these these geometrically the same?
RE: are these these geometrically the same?
The tolerance scheme on the right side of your first downloadable attachment "gdt_question.PNG" seems perfectly valid and reasonable to me. Note that the tolerance zone for datum feature B will be centered on the datum plane, so half of it (.015) will be unavailable. If you want the same .030 tolerance zone available for all four surfaces, you will have to adjust things a bit. There are several ways to accomplish this in ASME Y14.5-2009.
pylfrm
RE: are these these geometrically the same?
To accomplish your goal: I recommend you remove the Datum B feature from the profile control. You would remove the all-around symbol and apply the profile to the three remaining sides - I suggest using the "between" symbol (line with arrows on both ends). I would then add flatness to datum B to control its form. The FCF would have A then B datum sequence.
Certified Sr. GD&T Professional
RE: are these these geometrically the same?
that's exactly what I was afraid of. Wasn't sure if there was something I didn't know in the standard that "shifted" the window for cases like this but I guess that could get rather confusing in other circumstances.
mkcski,
perfect, that makes sense. I guess the way I look at it is first qualify datum B and then profile the edges relative to B. genius
RE: are these these geometrically the same?
Of note: it is NOT good practice to let an inspection method determine the tolerancing schema. Design intend - I call it "part function and fit-up" - should be the driving focus. Input from Mfg an QA must be considered - ya gotta make the part at a profit - but the part must "work" in the end.
Certified Sr. GD&T Professional
RE: are these these geometrically the same?
RE: are these these geometrically the same?
Certified Sr. GD&T Professional
RE: are these these geometrically the same?