Composite position

[Bob Pierce]

Can anyone tell me how to dimension the composite position using v4.1?
I know we are looking for concentricty, but if I dimension using concentricty then I loose my possible bonus.
Datum A is the underneath surface datum B is the center of the tube.


composite.jpg


Thanks

[TigerShark]

the composite FCF is wrong, if you notice, there is no datum called for second lower part of the composite, in deed I would say this is not composite, it is two true position that are attached together , because there are two time true position Sign ( one is used for upper FCF and another one is for lower). and this means this is not indeed a composite and from other hand that is Wrong ( no datuming refering to).

I have seen too many wrong GD&T like this, the engineer need GD&T training, that is the way to program your CMM

[Wingman]

TigerShark is right. This is not a correct FCF (with one possible exception). In all liklihood they are looking for Position to Datum C and are considering the two holes a 'pattern'. You can actually get by without calling a Datum in the 2nd part of tghe FCF but you have to have a pattern (at least two features controlled together). When yoiu have a pattern the lack of Datum in the FCF implies toleranced to the pattern, which is OK. Perhaps there is a pattern of features defined on the missing portion of the print?

I have not used PC DMIS 4.1 Composite Tolerance Capabilities; however, you should be able to enter them in directly as shown on the print (other CMM software that allows composite tolerancing works this way). You MUST have some feature to reference the 2nd portion of the tolerance to. Like I said, from what is shown it 'appears' that Datum C was intended but if that is the case then C should be part of the FCF. Unless there is a defined pattern someplace on the print then the FCF is wrong and you need clarification from the owner of the print.
HTH,
Bill

[dwade]

Atcually the FCF does not require a datum. The standard allows this and it is looking for coaxiality bewteen the 2 features (see fig. 5-53 on page 149 of the standard).

Set datum diameter -C- as your primary datum (measured as a cylinder if enough surface is there) then tolerance the smaller diameter.

[Wingman]

Atcually the FCF does not require a datum. The standard allows this and it is looking for coaxiality bewteen the 2 features (see fig. 5-53 on page 149 of the standard).

Set datum diameter -C- as your primary datum (measured as a cylinder if enough surface is there) then tolerance the smaller diameter.

That is what I just told him - sort of. I know the standard does not require a Datum. But, I'm not so sure you could use a Datum for the 2nd Feature unless you call it out or define it as the 2nd feature involved. In fact, I have NEVER seen a composite where the 'pattern' was not clearly spelled out on the print. Without a Datum Reference OR a defined 'pattern' it would leave it to interperetation as to which feature was involved and I have a hard time believing this is allowed (I have never personally allowed it or seen it - If I had seen it I would certainly ask for clarification). Are you SURE it is entirely legal without a clear definition of what the 2nd position callout in the FCF is referring to? It could be referring to a spacing to another set of holes in the part or even a pattern of many holes.

[Bob Pierce]

I am certainly not an expert in GD&T... I would agree with Tigershark that the correct way would be only one true position symbol tied to both call outs and with Wingman that clarification is in order.
This is a probable error of some type on the part of the designer.
Their is no specified pattern anywhere on the drawing.
I know the designer is wanting coaxiality.
I will attempt to locate the reference standard to convince myself, but I will be dimensioning as Dwade sugeested.
I appreciate all the inputs as I have much to learn.
Thanks

[Wingman]

I am certainly not an expert in GD&T... I would agree with Tigershark that the correct way would be only one true position symbol tied to both call outs and with Wingman that clarification is in order.
This is a probable error of some type on the part of the designer.
Their is no specified pattern anywhere on the drawing.
I know the designer is wanting coaxiality.
I will attempt to locate the reference standard to convince myself, but I will be dimensioning as Dwade sugeested.
I appreciate all the inputs as I have much to learn.
Thanks

Just one thing. Datum C is the smaller diameter, right - sure looks like it opoints to it in the section view that you posted? For the Composite Toleracne you need to fisrt set to ABC and report the 1st half of your Composite FCF. Then set to Datum C and repoort the 2nd half of your FCF. In both cases with the composite you need to report the location of the clearance hole and not Datum C - the smaller diameter. This is the commonly accepted way of doing it if your CMM Software does not allow composite toleranceing - some do and some do not.
HTH,
Bill

[Bob Pierce]

You are correct concerning datum C feature.
It is the smaller holes
Thanks Again

[cmmguy]

I believe the lower FCF only applies to itself and not to the other feature(smaller Hole), It is like a Perpendicularity callout. for the larger hole.

For it to be called out tot he other coaxial hole, that other hole would need a datum callout on it. I dont believe you can imply an FCF to another feature without calling it out specifically, but you can call one out to the same feature.

[kbotta]

This is not a composite position req't per 14.5 but rather a 2 single segmented feature control frame position req't. For the best explanation - see 5.4.1.3 of ASME Y14.5M-1994 pg 107...

[inspector212]

Knowing what A and B were would help in understanding the print and application of the FCFs.

The position callout to the 6.86 dia hole is incorrect. It can not reference C because it is C and you can not position a feature to itself.

The profile of 2 is also incorrect. Profile can not have a modifier applied to its tolerance.

Why is the width of the double "D" shaped hole positioned to B/A but the dia part positioned to A/B/C?

The callout is not composite position. It is two single-segment FCFs.

The callout is legal and correct but I think wrongly applied. The lower FCF is saying that a pin with a dia of 12.34 must pass through the hole. It is a pass-pin requirement.

A "BOUNDARY" position callout may have been a better choice here. It's is hard to say without knowing the function of the features.

[Wingman]

I believe the lower FCF only applies to itself and not to the other feature(smaller Hole), It is like a Perpendicularity callout. for the larger hole.

For it to be called out tot he other coaxial hole, that other hole would need a datum callout on it. I dont believe you can imply an FCF to another feature without calling it out specifically, but you can call one out to the same feature.

Not sure I follow you. Are you saying that the two holes (Datum Hole AND the Clearance Hole) are the Same Feature?

[inspector212]

Guessing what the engineer's intention is and what his/her actual intention is maybe two very different things. The print needs to be corrected by the engineer and given an explaination what what he/she did wrong or the next inspector will have the same questions and inspect it differently.

[Wingman]

If that is the case then the 2nd half would 'require' a Datum Reference. Thsis is a reply to the statement that these are two single segment FCF's. In the case of a positional FCF that stands alone (not part of a composite 'pattern' then the Datum Reference is 'required'.

[Wingman]

Guessing what the engineer's intention is and what his/her actual intention is/maybe two very different things. The print needs to be corrected by the engineer and given an explaination what what he/she did wrong or the next inspector will have the same questions and inspect it differently.

Agreement here!
This print is all messed up.