Composite Positional Tolerancing & Simultaneous Requirement RFS

[KENAT]

I have a part I'm checking that has 2 distinct patterns of holes, a set of 6 counterbored holes and a set of 2 threaded holes.

Both sets of holes use composite position with the same datum features (faces so RFS).

Am I correct in thinking that the 'Simultaneous Requriement' only applies to the Pattern Locating Tolerance Framework (top line of FCF)?

I'm looking at ASME Y14.5M-1994 5.3.6 & 5.4 and don't see it explicitly listed but it's the only way it makes sense to me.

KENAT,

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[PaulJackson]

Yes

 

[ringster]

Kenat,

Rather interesting. Are you checking it for functionality or merely for conformance to the Standard? Any chance of a sketch and what version? Is physical ident of the datum features enter into the equation?

 

[KENAT]

Both, the functionality is what takes so darn long sometimes, and there is implicit physical identification of the datum features due to geometry of the part.

I'm waiting to hear from the engineer wrt the functional requirement of the composite profile as it wasn't clear to me how the value was determined.

I don't think it's worth the effort of a sketch, and if you mean version of the standard it's in my OP, but thanks for the interest.

KENAT,

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[ringster]

Kenat,

Don't know if this will help much, but when read 5.3.6, it does not require the patterns to be checked with the same setup, but allows that they may be.

Is the PLTZ rectangular or circular? (no direct bearing on your question)

 

[powerhound]

ringster,
If the two patterns are specified WRT the same DRF and at the same material condition then they are a pattern and must meet their requirements simultaneously. This means you can't check one set of features, then move the part in order to make the other set of features come into tolerance. Using the same set up is how this would be checked. Using different setups completely invalidates the simultaneous requirements of the part.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ringster]

I have always thought that a DRF was repeatable. If it is, what is the difference whether a separate setup is made or checked simultaneously.

With reference to Fig 5.17 of the 1994 Std, what would be the difference if simultaneous or separate requirement imposed??

 

[KENAT]

PLTZF is circular at present, I haven't got to the bottom of all the functional requirments. It is possible that a square PLTZF would be appropriate.

KENAT,

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[DesignBiz]

It seems reasonable to me that the upper horizontal segment (PLTZF) would be subject to the simultaneous requirement relative to other FCFs with the same callout.
The FRTZF would not.

I would base this position on 5..4.1 which states that the PLTZF and FLTZF may be verified separately. To me this allows the PLTZF callout along with other patterns and features to be checked in compliance with the simultaneous requirement rule, were the FLTZF would be another separate verification.

DesignBiz

 

[axym]

Ringster,

DRF's are generally not unique, and not necessarily repeatable. Y14.5.1 explains this in terms of "candidate" DRF's that occur in cases where the datum features can shift relative to their simulators. Such cases include datum features referenced at MMC or LMC, and "rocking" datum features.

Figure 5.17 refers to FCF's that reference three planar datum features. If simultaneous requirements were imposed, then both FCF's would have to be checked in the same rocking position. If separate requirements were applied, then the datum features could be rocked differently for each FCF.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[ringster]

Evan,

For a minute without regards to the Standard, if the DRF is not repeatable to the extent necessary to very the controlled dimension and its respective tolerance, I think we have a problem.

 

[WHITMIREGT]

One thing you need to remember about composite position, the datums are for orientation only.

 

[powerhound]

ringster,

For the sake of simplicity, let's consider fig. 5-18. As the example shows, the 2 hole patterns are separate requirements which means they don't necessarily have to be oriented as shown. The 2 large holes have to be oriented 180 degrees apart as do the 2 small holes but each hole pattern does not have to be oriented 90 degrees WRT each other. They are 2 separate 2 hole patterns with no relation to each other and not a pattern of 4 holes. If the SEP REQT were not there, then it would be considered a 4 hole pattern and all the holes would have to be oriented 90 degrees apart.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ringster]

Powerhound,

On the surface it is a fairly simple example and I understand what you have stated. However, I must ask that
if the hole patterns are not 90 degrees apart, just what is the allowable deviation. I thought we have a rule that covers 90 degree relationships of centerlines on drawings.

If orientation is of no concern, why introduce C?

One thing that concerns me as an example in the standard is that you really don't know which surf is A. It needs PHYSICAL IDENT.

Ringster,
RGHC Checker

 

[PeterStock]

The allowable variation would be that the two hole patterns would both need to meet there own FCF. As such the patterns would be within 0.5+0.7 = 1.2 to each other at MMC with B and C at MMC. The tolerance of the features would need to be taken into account for other than MMC

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[DesignBiz]

Not so sure when we get to repeatable DRF's and examples with sep reqt that we simplify or answer the original question.

Considering the PLTZF can be verified separately from the FLTZF, it would appear that PLTZF(s) would need to follow the simultaneous req rule in regard to other FCF's with the same DRF and material conditions.

DesignBiz

 

[ringster]

Kenat,

I believe that to ans your orig post, the answer would be that 'Simultaneous Requirements' does in fact apply only to the PLTZ.

 

[KENAT]

Didn't we work that out a couple of days ago;-).

As regards

One thing that concerns me as an example in the standard is that you really don't know which surf is A. It needs PHYSICAL IDENT.

You seem to forget paragraph 1.1.4 of the ASME Y14.5M-1994 standard.

KENAT,

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