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SIM REQT with multiple composite tolerance FCFs in one view with multiple feature patterns 5

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Tunalover

Tunalover

Mechanical
Mar 28, 2002
1,179
Suppose we had a flat, rectangular plate of, say, aluminum. And say we had three datums A, B, and C as primary, secondary and tertiary datums assigned to the largest flat surface (A), the longest edge (B) and the shortest edge (C).

Lets call out a 12-member pattern of simple holes at diameter d1. Then lets call out, say, a 6-member pattern of simple holes at diameter d2. Now let's add a 8-member pattern of identical slots.

If each pattern possessed its own composite positional tolerance FCF with the same datums in the same order of precedence, will ALL of those features default to a single pattern even if they are geometrically different? Or will each pattern default to a SEP REQT? Or is it something else? I've always been confused on this.

ElectroMechanical Product Development
(Electronics Packaging)
UMD 1984
UCF 1993
 
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If you mean they all use [A|B|C] as their datum references, they they are all checked at the same time, simultaneously, with respect to orientation and location of the part with respect to the datum features.
 
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Only the upper segments of the composite callouts are subject to simultaneous requirement. Regardless of geometrical shape of the considered features.

The lower segments, by default, do not have to be gaged simultaneously.
 
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Sorry - when I saw the word "simple" to describe the patterns I missed the suggestion of the complex application of composite tolerances.

A potential result of the independent evaluation of the lower segments among the various patterns in MMC conditions is that the related parts can be forced out of alignment with each other because the MMC lower range will prevent sufficient float to allow orientation/location adjustments.
 
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Assume the top segment of each FCF has |A|B|C| and the bottom segment has |A|.

The tolerance values can all be different except, of course,the tolerance values in the lower segments are less than the values in the upper segments.


ElectroMechanical Product Development
(Electronics Packaging)
UMD 1984
UCF 1993
 
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Y14.5-2009 4.19 Simultaneous Requirements - "...A simultaneous requirement applies to position and profile tolerances that are located by basic dimensions, related to common datum features referenced in the same order of precedence at the same boundary conditions...This principle does not apply to the lower segments of composite feature control frames..."

What is interesting to note on your example is that it really does not matter if you gage/measure each pattern individually or as one composite pattern because there is no possible datum shift. Simultaneous requirements is something to pay attention to when the datum features are referenced at MMB/LMB. Figure 4-39 shows an example of simultaneous requirments when datum shift is allowed.

 
 https://files.engineering.com/getfile.aspx?folder=a135751c-30fe-43b6-ab48-5f04ebf7cbac&file=4-39.JPG
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Andrew,

Not too long ago was a discussion here ( about the correct name of the "datum feature shift" versus "datum shift"

Not sure in your replay, you might want to revise it to : "What is interesting to note on your example is that it really does not matter if you gage/measure each pattern individually or as one composite pattern because there is no possible datum FEATURE shift. Simultaneous requirements is something to pay attention to when the datum features are referenced at MMB/LMB. Figure 4-39 shows an example of simultaneous requirments when datum FEATURE shift is allowed. "

Am I correct?

Do you agree what is not such of "animal": datum shift? The correct name should be "datum feature shift"

I am interested in this subject and that is why I am questioning.
 
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Well, 4.11.9 is titled "Datum Feature Shift/Displacement", so that leads me to agree with you that the term should be "datum feature shift" and/or "datum feature displacement". But the last sentence of 4.11.9 states "...and datum shift or displacement is not allowed". That sentence leads me to think that both terms (datum feature shift/displacement and datum shift/displacement) are acceptable. I suppose that last sentence could also be a typo and they meant to write "datum feature shift or displacement".

I have also heard it called "tolerance shift" by some.

I'm going to have to think about what terminology I am going to use going forward.
 
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AndrewTT said:
What is interesting to note on your example is that it really does not matter if you gage/measure each pattern individually or as one composite pattern because there is no possible datum shift. Simultaneous requirements is something to pay attention to when the datum features are referenced at MMB/LMB. Figure 4-39 shows an example of simultaneous requirments when datum shift is allowed.
Click to expand...

I disagree with that.

First, the default rule saying that lower segments of composite FCFs are not subject to simultaneous requirement means that all 26 position tolerance zones defined by the lower segments in tunalover's example do not consitute a single pattern, but there are 3 separate patterns instead:
1. Pattern of 12 cylindrical tolerance zones for simple holes at diameter d1.
2. Pattern of 6 cylindrical tolerance zones for simple holes at diameter d2.
3. Pattern of 8 width tolerance zones for identical slots.

If the design intent is to make all the 26 tolerance zones a single pattern, the composite position callout should be changed to multiple-single-segment FCFs.

Second, the definition of simultaneous requirements given in 4.19 does not say anything about necessisity of having datum features referenced at MMB (or LMB). The attached Tec-Ease tip has been used on this forum many times before:
 
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The second GD&T scheme in that Tec Ease example has shift available between the part and gage. You could revise my statement to say that simultaneous requirements is something to pay attention to when shift is available (most times this comes from datum features being reference at MMB). My point was that if no shift is available then it really does not matter if you check the upper segment of the FCF for pattern 1, then pattern 2, then pattern 3, or check them all at once.
 
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AndrewTT said:
My point was that if no shift is available then it really does not matter if you check the upper segment of the FCF for pattern 1, then pattern 2, then pattern 3, or check them all at once.
Click to expand...

I wasn't talking about upper segments of the composite FCFs. I was talking about lower segments.
 
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If the as-manufactured datum features are not perfect then it is possible to have a variety of possible orientations from nominally planar features. By picking how the part is inspected one can affect the outcome.
 
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Pmarc, I was always talking about the upper segments.

3DDave, valid point. It the part can rock on the datum simulator then you would need to check all 3 patterns at once.
 
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Tunalover,

The upper segments of the composite callouts in your example create a pattern of 26 tolerance zones. This means that all the 26 features should be gaged simultaneously when checked for conformity with the upper segment callouts. The shape of the zones does not play a role.

The lower segments of the composite callouts create 3 separate patterns:
1. Pattern of 12 cylindrical tolerance zones for simple holes at diameter d1.
2. Pattern of 6 cylindrical tolerance zones for simple holes at diameter d2.
3. Pattern of 8 width tolerance zones for identical slots.

This means that each of the 3 patterns of features should be gaged simultaneously when checked for conformity with the lower segment callouts, but there is no requirement to gage all the 26 features at the same time. Again, the shape of the zones does not affect the answer.

Does that answer your question?
 
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Pmarc,
Is there any way in ASME to unlock the inter-relationship within the patterns? I guess SEP REQT (which is default anyway for FRTZF) won't do it,right?

In other words how to make the 12 holes with diameter d1 (OR the 6 holes with diameter d2 OR the 8 slots) having an independent relationship from each other?
 
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greenimi,

What exactly are you looking to accomplish or what do you mean by "unlocking"? If you notate separate requirements, each of the 3x groups of patterns will still be related back to the same datum structure, so even if they aren't held together as a continuous 26 feature pattern (ie: gauged/measured together) they are still interrelated insofar as they are held to the same DRF.
 
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