Redundant or not? Please help

[greenimi]

Imagine a shaft --datum A-- Ø.365/.360-- with 2 thru holes 2x Ø.195/190--positioned with ± .185/.165 tolerance from each end of the shaft.
A slot is added to this shaft in the middle (equal distance from both ends). The slot is .100/.090 and is called datum B
The GD&T is as follow:
For the holes: multiple single segment (not composite )
2x
position of Ø.002 at MMC to A at MMC--first segment
and
position of Ø .004 at MMC to B at MMC--second segment--

For the slot (datum B): position of Ø.002 at MMC with A at MMC

The question for you is: the second segment of the multiple segment callout, isn't it redundant callout?

Simultaneous requirement is implied, since the slot and the holes have the same datum reference frame (positional at MMC to A at MMC). Please help.
Again, I am thinking that position of Ø .004 at MMC to B at MMC--second segment--is redundant, but I am not sure.

 

[fsincox]

Different datums means different reference framework setups, I suspect it is wrong, but, it is not completely redundant.
The centerplane of Datum B, by itself will not really establish a cylindrical zone control, while it is not actually wrong to use it it seems like it is not really what is desired, Without a functional assembly definition who knows?
Frank

 

[greenimi]

I managed to get a picture for the applicable callouts in question. Hope this helps.

 

[dgallup]

First, I don't think the second position to B is in any way redundant. Without it the holes could be completely misaligned with the keyway.

Second, the true position call out on the keyway is incorrect. There is no way this can be a cylindrical tolerance zone.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[fsincox]

Thank you,
I stand by what I said, Understaning the difference in the effect of datum B as primary vs just A(primary), or A(primary), B(secondary) which I suspect is actually more of the functional requirement requires a more complex analysis than I have to review quickly now here. It would be easier to build the functional gages, which is why the standard uses this method.
Frank

 

[fsincox]

Now that we have a drawing, I agree the cylindrical zone on the keyway is incorrect, period.
Frank

 

[greenimi]

To dgallup:
I agree with your second statement. No diametral symbol Ø on the tru position callout on the keyway.
As far as the first statement, I am inclined to disagree because the simultaneous condition. See the standard ASME Y14.5 -2009 page 80 --the same is applicable on the 1994 standard.
Am I missing something? The keyway must be alligned withthe holes due to the same datum reference frame which means simultaneous condition, right?

 

[greenimi]

To Frank: " Now that we have a drawing, I agree the cylindrical zone on the keyway is incorrect, period.
Frank"

Here everybody --including me --agree. No Ø for the keyway callout!

 

[fsincox]

Today IS a good day, here
Frank

 

[dgallup]

"same datum reference frame" - Datum A by itself does not constrain the the part from rotating. I still think you need the second frame, particularly since it has a different value.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[fsincox]

I understand your conclusion is based on the simultaneous requirement I am just uncomfortable saying it is the "exact" same result without serious study, I prefer do not do that. I have been a firm advocate of differentiating things like: perpendicular to A and perpendicular to B is not the same as perpendicular to A(primary), B(secondary). I see many people make this assumption. In this case it may result in the same if you analyze it I have not, it is not automatic.
I have also said I suspect I would have not done it that way.Then when you add a: "do I care that much about this particular feature", you may be there.
Frank

 

[fsincox]

My suspicion is that since the keyway is relatively short and the hole spread is 4 or 5 times as great, the projection of the datum alone will allow for an increased tolerance would not be allowed by the "simultaneous requirement".
Frank

 

[fsincox]

The holes are not defined with basic dimensions so those cylindrical tolerance zones are suspect, too. now that I have had more time to review an actual drawing.
Frank

 

[MechNorth]

Try this instead;
a multiple single segment position control within dia .004(M)/A(M)/B(M) on the first level, and within dia .002(M)/A(M) on the second level.
This allows the greater position wrt datum-B, with a refinement wrt datum-A, including the inter-feature relationship. I think that was the design intent. Datum feature B is related back to datum-A, so tying the two controls together as a composite makes sense.


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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[fsincox]

Jim,
The OP was: "is it the same" (redundant), I assume you agree it is not the same?
Frank

 

[MechNorth]

That's right, Frank. I figured showing a correct "how to" would help illuminate why it's wrong in the first place.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[greenimi]

Quote:
"Jim,
The OP was: "is it the same" (redundant), I assume you agree it is not the same?
Frank "

Jim,

Yes, my original question was the following:
- As is now the drawing defined (not as should have been) is the second positional requirement (the one from the multiple segment) redundant or not, taking in consideration impled simultaneous requirement rule, which is aplicable in this case--

Jim ,
Thank you for your input on how the drawing should have been at the begining to most likely meet the design intent, but unfortunatly did not end up like should. Therefore, created questions and I needed your input.

 

[MechNorth]

Then yes, it is redundant. The tighter control already establishes a more restrictive tolerance and the second control is redundant.

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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[CheckerHater]

This may not be directly related to OP, but is everyone here comfortable with using Diameter symbols AT ALL?

As holes are located North-South via FCF and East-West via directly toleranced dimensions, is tolerance zone really cylindrical?

 

[greenimi]

To CheckerHater (Mechanical)

I agree with you that this print needs a lot of work (including Ø symbol usage, missing basic dimensions, combination between ± dimensioning and GD&T and so on), but the original question was if that callout is redundant or not pretending everything else is as per the standard.
In other words, if the designer revise this drawing per the standard Y14.5-1994 and everything now is fully defined and legal, but is keeps the same GD&T structure, is that structure redundant or not. That was the original question and I want to understand the concept and the "conflict" (if any) between these GD&T requirements. I hope this helps.