Is my understand of the FRTZF correct?

[rollingcloud]

My main concern is the distance between the char 36 (Ø0.312 - Ø0.314) hole and the char 40 (Ø0.377 - Ø0.379) hole. This distance is not explicitly shown on the drawing, but it can be calculated in its basic form using char 49 and char 59 & 60, yielding 0.8133. My goal is to determine the smallest possible distance as a result of the FRTZF or how much that .8133 will be decreased by.

Since the FRTZF has a 0.007 diametrical tolerance zone and the distance between the holes in the Y-direction is not controlled by the FRTZF, only char 49 is directly affected by the 0.007 tolerance. In the worst-case scenario, the new distance between the holes would be: 0.8133 - 0.007 = 0.8063. Can someone confirm if my understanding is correct?

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(On a related note, I noticed some questionable aspects of this drawing. For example, is char 37 even valid? The PLTZF has a basic dimension for the Y-direction (char 59), but the X-direction is not defined using a basic dimension. Instead, it relies on dim Q, which has a tolerance relative to the edge (not a datum).

That said, I suppose it's still somewhat interpretable. Perhaps the intention was: "The hole location in the X-direction must first meet dim Q, and then its Y-location must conform to char 37." Essentially, this approach mixes hard dimensions with basic dimensions—though separately. Just not sure if its legal per Y14.5.)

 

[Garland23]

I'm not ready to dive into this one with a full answer, but I do know that lower segments of composite position (items 61 and 62) are not simultaneous requirements, even though they have the same datum reference. So the .007 doesn't itself tie the positions of those two holes to one another.

 

[3DDave]

Datum feature B does not fix any degrees of freedom in the [A|B|...] reference frame for features that are nominally perpendicular to [B ] , such as all the holes.

The composite tolerance that uses [A|B] in the upper segment and alone in the lower to determine characteristics (37) and (61) is invalid.

The horizontal location would not be required, given realistic datum feature references, as the lower segment might apply if there were two coaxial holes, but that also doesn't seem to be the case.

With position tolerance characteristic symbols in feature control frames, there is no "must meet a dimension". By default, all features like that automatically meet that dimension; it's a basic dimension that locates the true position. What is measured is the variation from that true position.

 

[greenimi]

All the composite callots are incorrect/ illegal.
You may want to have A primary in the lower segment OR you may want to switch to multi single segments (and keep B primary) is functional requirements are such.
Also, B is not related to A with perpendicularity.

 

[Burunduk]

I agree with the others.
According to composite tolerancing rules, any datum references repeated in lower segments, must keep the same order of precedence as in the upper segments.
So you basically need to make up your mind how your part needs to be constrained for the evaluation of the holes - should A or B be primary? The decision should reflect the function - how will this part be assembled and what feature stabilizes its initial orientation (2 rotational degrees of freedom)?

Then you can only repeat the primary datum as primary in the lower segment as long as it's composite and not two single segments. But, in your case, it will only tighten the orientation of each hole to that primary datum (or relative to a datum reference frame established from the primary and the secodary, if the secondary was also added). The two separate lower segments in the composite tolerances will not solve your hole to hole distance problem, as they will not create a simultaneous requirement between them, also according to composite tolerancing rules.

The tightening of hole to hole relationship by lower segments is only when the holes are controlled as a pattern.

As you currently toleranced this, it is the segments that reference C that control hole to hole distances.

 

[3DDave]

Can't edit - I didn't notice that the f'n software eats certain letter combinations and turns them into bolding control.

"The composite tolerance that uses [A|B] in the upper segment and alone in the lower to determine characteristics (37) and (61) is invalid."

Should read:

"The composite tolerance that uses [A|B] in the upper segment and [B ] alone in the lower to determine characteristics (37) and (61) is invalid.