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Composite Positional Tolerancing? 1

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pmarc

pmarc

Mechanical
Sep 2, 2008
3,227
Hello,

Short question:
What is the difference in interpretation of following two cases of composite positional tolerancing?
I know what Y14.5M standard says, but I am afraid I am not able to visualize this difference properly.

Thanks a lot for any hint.
 
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The top one with the A datum ref in the FRTZF is also refining perpendicularity of the holes.

The bottom one would allow the entire pattern to 'tilt' within the tol limits.

I know you've looked at ASME Y14.5M-1994 but make sure and read 5.4.1 section b bottom line of page 95

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: What is Engineering anyway: faq1088-1484
 
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In the one without [A] there is no requirement that the pattern of six variable size cylindrical tolerance zones 0.2 at MMC, 0.4 at LMC or the pattern of 6 maximum material boundaries of diameter 5.7... be perpendicular to [A] beyond that which is required by the upper segment.

In short it contrls the pattern integrity only not that pattern's orientation to [A] as the lower segment of the upper composite control does.

Paul
Paul
 
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pmarc, view the following PowerPoint file, which illustrates graphically what you are asking. The first slide shows the FRTZF (bottom line of the composite positional tolerance) without invoking Datum-A. The second slide shows the FRTZF with Datum-A invoked. I use this in my training, so I haven't added the verbal commentary that I usually include in class.


Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Jim, Thanks for the PowerPoint slide, it’s very clear and easy to understand the differences in between, but I am anxious to know the differences between them if multiple single segment position tolerance called out for this case.

POS|Ø0.6MMC|A|B|C
POS|Ø0.4MMC|A|B
POS|Ø0.2MMC|A

SeasonLee
 
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Interesting. There is no support in the standard for 3 single-segment position controls as you show here. Two, yes, but not 3.
I'll see what I can come up with for graphics for 2 single segments, and give the 3 segments some thought.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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There is no example of 3 single segment positional FCFs in the standard but, as ProfDon stated, not everything is covered by examples in the standard.

The first positional tolerance of DTZ of 0.06 mm controls the pattern (PLTZF) for location from datums B & C and perpendicularity to datum A.

The second positional tolerance of DTZ of 0.04 controls individuals (FRTZF) in the pattern to each other, perpendicular to datum A and parallel to datum B. The single segment FCF also controls the dimension or location from datum B to the pattern. This differs from a composite feature control frame where the individuals in the pattern are only parallel to datum B rather than parallel and dimensioned.

The third position tolerances of a DTZ of 0.2 control the individual features in the pattern (FRTZF) to each other and perpendicular to datum A.

Dave D.
 
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Jim and Dave : Both of you mentioned there is no support in the standard for 3 single-segment positional control, but I can see a lot of examples from either Alex Krulikowski “Advanced concept of GD&T” or Al Neumann “Geometric Dimensioning and Tolerancing Workbook”, it makes me confused.

SeasonLee
 
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Oh no. Another question about the legality of something that the standard doesn't specifically mention.

I think it's fine, as long as the considered feature is perpendicular to one datum and parallel to the other ;^)

Evan Janeshewski

Axymetrix Quality Engineering Inc.
 
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As Prof Don stated? ......no respect.

Extension of Principles

Did someone just pass out a bunch of those books?
 
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Dave, I was thinking of that explanation as well, but in that case I'd have used a single segment followed by a composite control; more directly intuitive. Of course that's not in the standard either, but it guides me better than 3 single segments. What makes the 3-singles non-intuitive to me is that the second (and presumably subsequent) FCF also refine the location with respect to the datums. This may be valid if the feature can be located wrt the Datum-A, but otherwise would just provide a refinement of inter-feature location and orientation wrt the Datum-A ... which is a composite control.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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If you don't mind, I would like to go back for a moment to the original question for composite postional tolerancing:
As SeasonLee said, Jim's PowerPoint slide shows very clearly the difference in between. But my question is can axes of these 2 holes be tilted in different directions if no datum is specified in bottom segment of FCF (so that they are not parallel to each other)?

 
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Sorry, I actually meant: can tolerance zones of the axes of these 2 holes be tilted in different directions if no datum is specified in bottom segment of FCF (so that the tolerance zones are not parallel to each other)?

 
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Yes, I think so, they can tilt in different direction as long as the tilt within tolerance zone.please correct me if I am wrong.

SeasonLee
 
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No, the zones can't tilt in different directions. The zones are parallel to each other, even with no datum references. So the position tolerance would control the relative parallelism of the holes, and their spacing.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
 
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Let’s go back to multiple single segment position tolerance callout.

There are a lot of 3 single-segment position tolerance callout examples on the two books mentioned above not only on the text but also shows on the exercise, I am asking the differences between them since I believe Jim will have an better and excellent interpretation.

SeasonLee
 
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SeasonLee,
I have Alex's 'Advanced of GD&T Concepts' in front of me, and at the end of chapter 20 there is an exercise 20-1 which shows exactly the same situation like you are asking about. I am sure you noticed the statements in point 5 (page 20-13):
- top segment controls location of pattern relative to A, B, C;
- middle - location to B;
- bottom - spacing between holes as well as squarness to surface A.
I am not sure what does the 'squarness' exactly mean, but I assume it's simply a perpendicularity to A.

Regards
 
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pmarc

The 3 single-segment position tolerance callout on the exercise is

POS|Ø1MMC|A|B|C
POS|Ø0.5MMC|A|B
POS|Ø0.2MMC|A

My understanding the squareness to surface A is the pattern (4 holes) perpendicular to datum A.

SeasonLee
 
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Bear with me. I'm trying to get a couple more graphics done so I can put a bunch of scenarios into one file. Might try to add a voice narration too.

My Krulikowski reference books stayed with the old employer, so I can't comment on differences between his examples. If someone were to send me a scan, I could take a look.

The points pmarc presents from Alex's book make sense and don't contradict anything in the standard. In theory, then, you could have 5 single-segment position controls, though that wouldn't be useful as far as I can figure.

As for "squareness", indeed it does mean perpendicularity. It's a hold-over term long used in the shop, and is commonly used and understood by most of us "old-timers" that grew up with heavy interaction between shop and design ... ah, the painful memories of lessons past.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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