Mismatch and profile tolerance

[prdave00]

Attached is an example of a molded part for illustrative purposes only. My question regards how to account for mismatch in a profile tolerance relative to a datum A.

In the example, the feature to the left of the parting line (A-plate side) has a profile tolerance related to a datum feature A on the right side of the parting line (B-plate side with core pin). Taking the leap that my design can tolerate the mismatch allowance and the profile tolerance guarantees function in the presence of mismatch, how do I (or do I need to) communicate on the drawing that the profiled surface can shift to the left/right of the datum A (but not datum B) by the mismatch allowance. Will the boundary principle (6.5.5.1 of ASME Y14.5M-1994) also shown in the attached file work here or is it now additive (i.e. the profile can shift by the amount of mismatch + the positional tolerance)? Anyway to remove any and all ambiguity?

 

[prdave00]

Sorry file didn't upload right.

 

[SeasonLee]

Prdave00, here are my comments on the post :

1. Mismatch will only happened on the parting line area, datum feature B is the parting line surface but the deviation on the possible part is around the polygon on your sketch. If your intention is trying to control the polygon, then the mismatch on the note column is not appropriate.

2. In order to tolerance the polygon, you may use profile callout to control the size, location, orientation and form of the polygon, be sure to use the all-around symbol since it will apply to all sides of the polygon. Please ref to the attached file to see how profile control will limit the “shift or mismatch”.

3. Position boundary is normally used on irregular shaped opening or slot, I will not recommend to control the semi sphere with position boundary.
|profile|.010|A|B| will be more suitable for this case since it will not only to control the size and form but also location and orientation.

SeasonLee

 

[prdave00]

Season Lee:

Thanks for the comments. The drawing is definitely incomplete (hence no tolerancing for the polygon feature) and I agree that a profile tolerance would be the best to control the polygon surfaces. However, my question regards the relationship between the domed surface and the blind hole features in the opposing mold halves. To your point, given that datum feature A and the polygon shape are on the same side of the mold, mismatch does not factor in. However it does for relationship between features that I'm concerned about.

Referring to the attached revised drawing (slightly tweaked from the OP), granting me that I've designed the part and established the profile tolerance for the domed feature with the mismatch in mind, I'm worried that someone reading the drawing may interpret that the profile is "locked" to the axis of datum feature A. In other words, allowing a mismatch would shift the feature outside the profile tolerance.

I'd like to think I'm extending the BOUNDARY principal (i.e. combined controls) correctly, but I'm not so sure. The example in the standard uses a MMC modifier where my positional boundary is regardless of feature size and the position is a refinement where mine allows for more "slop". Maybe having the mismatch allowance noted covers the positional shift in relationship to datum feature A. My concern here, is that I've now communicated that a .010 radial shift in position + a .015 mismatch is allowed. I've also considered adding a note saying "The position of domed surface can shift along the parting line plane in relationship to the datum A axis as long as the surface profile requirement is met." I'm hoping someone has experienced this same dilemma and can suggest a way to alleviate any ambiguity.

By the way in response to "normal" use of the BOUNDARY principal, it's unfortunate that this principal is exemplified in ASME Y14.5-1994 (p. 171) and 14.5-2009 (p. 176 where the the term "BOUNDARY" is now optional) using an irregular shaped internal feature and in the TecEase tip (

http://www.tec-ease.com/premium/gdt-tips-view.php?q=129)

to control slots. I'm hoping there's more utility out there for combined controls than whats been exemplified.

 

[SeasonLee]

prdave00

I understood your intention now, I will recommend to control the domed surface with position control:
|Position|SØ.030|A|B|, where S indicates the tolerance zone is sphere, I still think the boundary is not suitable for this case.

SeasonLee

 

[SeasonLee]

Pls ref to Fig.7-35 in 2009 standard, its quite similar to your post.

SeasonLee