supergee's explanation is detailed and correct.
3DDave's first reply is extremely concise version and that's why he said as below.
" Or datum plane C is created by the center point of a line created by 2 points on each face while perpendicular to Datum plane A and Datum plane B.
-It could be a...
Per ISO 5458:2018, flatness and strainghtness can define a pattern and control not only the orientation but also the location of features in a group, but in condition that the features are coaxial or coplanar. So in OP's case flatness should not be used since the surfaces are not coplanar...
umatrix,
You may have two pins that are fitted on both sides of the bore, i.e. one pin at datum A side, and the other at datum B side.
They are press fitted and the protruded feature on each side stops the pin on corresponding side.
Considering these interaction of the bore, the stopper, and...
Consideration on assembly condition should be studied by the design engineers. I would just tell them the possible options for datum selection.
As you said, option 3 is legitimate too. But would it be practical for CMM inspection, because the local coordinate system is so far from the part?
Below is my study on DRF establishment (for CMM inspection) of different datum options when we want to make a hole a datum feature which has an angle with primary datum plane.
Like to here thoughts from the experts if my understanding is correct.
Overall shape of my part looks like this...
First I would like to thank you everyone to get interested in this post.
Then I also have to say sorry that I have left my question unclear and made everyone confused. Due to different time zone, and the urgent work / personnel matters, I missed leaving my response in the right time.
I meant...
Years ago, when my customer adopted MBD, its MBD construction guideline said that each MBD shall have a coordinate system and a datum reference frame as I recall, which sometimes made those useless for simple parts which do not need datum.
ASME Y14.41 Digital Product Definition Data Practice...
Thanks Galrand23.
What is still not clear to me is ISO. We can control the location of a cylindrical feature which is nominally coincident to datum axis by position tolerance, and concentricity tolerance.
Then why do they allow the use of symmetry tolerance as well? Maybe I misinterpreted...
Symmetry is removed from Y14.5-2018. So let's talk about 1994 or 2009 version.
What I understood about the symmetry so far is:
1. symmetry controls median points of tolerance feature
2. datum feature can be either a cylindrical feature of size or a feature of size that is composed of opposed...
3DDave:
Would you tell me more story?
greenimi:
That part of Y14.5 that you quoted just say that the tolerance zone is contained in the cutting plane.
That is not an answer to my question.
Is straightness of my part zero or not? That is my question.
Below figure is captured from Y14.5-2018.
Figure (d) was not there in 1994 and 2009, but appeared in 2018.
Say I have an actual part exactly looks like figure (d). The surface is perfectly straight, but tapered as in the figure.
This figure implies that straightness of the part surface is 0.02...
ISO 1101:2017, para 9.1.4 says "If the toleranced feature is a derived feature, the intersection with a feature can be identified as a limit of the derived feature"
While ASME defines a feature as a "physical portion of a part", ISO defines many different types of features and a derived feature...
This makes me interesting because some months ago I had a talk with my friend about the exact same issue.
One preferred using the Projected Tolerance Zone symbol as 3DDave suggested, the other one preferred using the BETWEEN symbol, that is, A <-> B, with A is the intersection of the centerline...
Position tolerance of the internal boss to what? Datum A the flat surface?
The internal boss does not have locational relation to datum A, thus the position tolerance to A would not make sense. Only the perpendicular tolerance to datum A would be needed for you.
Size of upper three holes and size of lower three holes are different. Composite position FCF is attached to one of the six holes with "6 X". Doesn't this make sense, without a note like "INDICATED"?
Thinking from the perspective of stability of datum system, if only A is used the part will rotate around the datum axis. When B is added, now the part is stabilized. Though one translation degree of freedom is not constrained yet, it does not affect the orientation of the hole.
The image of a surface plate with a hole is typically shown in GD&T textbooks. I though it was just to help grasp the concept of flatness verification and rarely used in the real world.
But many seem to say that the method is actually commonly used. Is it true?
I would appreciate if by any...
Draw a vertical centerline which crosses all horizontal outlines, then it would make ZERO BASIC dimension between the center of datum feature and centers of considered features.
chez311,
Yes, you are right. Because what constrains the tolerance zone is the actual DATUM FEATURE, not x, y axis of DRF defined.
But I am looking for if there is any logic allowed by Y14.5 that imaginary axis of DRF associated with (like, offset from) datum features or portion of datum...
You are correct until the above quote. Datum axis B is wandering on the plane of A because it has only perpendicular constraint to datum plane A.
Now look at datum feature C, whose position is constrained to datum axis B. Look at part note #2. All other feature's are constrained to A in...
