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Redundant or not? Please help

Redundant or not? Please help

Redundant or not? Please help

(OP)
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.
 

RE: Redundant or not? Please help

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

RE: Redundant or not? Please help

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.

----------------------------------------

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.
 

RE: Redundant or not? Please help

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

RE: Redundant or not? Please help

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

RE: Redundant or not? Please help

(OP)

 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?


  
 

RE: Redundant or not? Please help

(OP)
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!   

RE: Redundant or not? Please help

Today IS a good day, here :)
Frank

RE: Redundant or not? Please help

"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.

----------------------------------------

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.
 

RE: Redundant or not? Please help

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

RE: Redundant or not? Please help

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

RE: Redundant or not? Please help

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

RE: Redundant or not? Please help

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  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: Redundant or not? Please help

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

RE: Redundant or not? Please help

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  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: Redundant or not? Please help

(OP)
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.
  

RE: Redundant or not? Please help

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  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: Redundant or not? Please help


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?

RE: Redundant or not? Please help

(OP)
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.  

RE: Redundant or not? Please help

Thank you greenimi,

I started my post saying that it was more about "legal" then "redundant".

One of my concerns was that if the shape of tolerance zones are significantly different, requirements may be less redundant, but it is not the case here.

Also there is another fine line here. As datum [A] symbol is not aligned with 365/360 dimension, the datum [A] is NOT axis of the shaft, but rather something else, it creates different reference frame, and your requirements are NOT redundant.

There is no need to be defensive. I am just exploring possibilities. smile

RE: Redundant or not? Please help

CH,
I believe in the case of a cylinder, sphere or cone (without other  limiting indications) it is treated as the same thing.
Frank

RE: Redundant or not? Please help

Maybe in some places standard is more vague, but if you compare, say, Fig.3-4 and Fig.4-45 (Y14-2009) it's kinda specific.

RE: Redundant or not? Please help

Fig 4-45 is exactly the kind of thing I was thinking of.
Frank

RE: Redundant or not? Please help

I think a datum feature symbol doesn't have to be aligned with dimension arrows when dealing with a cylindrical part as the datum feature.  This is because there's only one way to interpret a datum on a cylinder: an axis. See Figs. 6-14 and 15 of the standard for an example.

The case of a planar feature of size is different, though, because there the datum symbol not aligned with the FOS would mean only a surface as the datum feature.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Redundant or not? Please help

Thanks, J-P, for the help.
This is the way it was explaind to me also, if I put a finish mark on the surface it is automatically applied all way around on a cylinder, sphere, or cone. so the standards are consistant in that sense.
Frank

RE: Redundant or not? Please help

Frank, JP,

Where exactly in the standard datum derived from cylinder is shown like in OP picture?

RE: Redundant or not? Please help

There would be an infinite number of tangent planes / lines that could be derived from the feature given the datum callout (A) in the OP figure.  If one of those were the intention, it would be referenced as a tangent plane (T) in the DRF and would need some specific basic dimensions/angles to locate it wrt other datums; it would not be an acceptable primary datum then.  
As there is no other reasonable interpretation, the interpretation leads you to the center axis; this is supported by the attachment of the datum callout to the cylindrical surface in an end view (see Fig.4-44 in'09, datum A).  Note that a similar situation arises when attaching the datum callout to the side-profile of a cone, as in Fig. 4-45 ('09).

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: Redundant or not? Please help

CH,  it's paragraph 3.3.2(c) of the standard:  The datum feature symbol may be "placed on the outline of a cylindrical feature surface or an extension line of the feature outline, separated from the size dimension, when the datum is an axis."   (That statement doesn't say that it has to be in a view where the feature looks like a circle; it just says that it may be placed on the surface of a cylindrical feature.)
 

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Redundant or not? Please help

Jim, we agree that datum A in the OP picture is the axis of the cylinder, not planes or lines formed from the top arc of the cylinder.   But if we really wanted lines or planes taken from the top, wouldn't a datum target be used?  I've never seen the "T" modifier next to a datum reference.  

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Redundant or not? Please help

JP,

Paragraph 3.3.2(c)states "see Fig.3-4, illustrations (e) and (g)" plain and simple.

I see no reason to continue this argument.

RE: Redundant or not? Please help

Didn't see it as an argument ... so you believe the datum callout in the OP drawing to be illegal?   Paragraph 3.3.2 doesn't verbalize every possibility; we've already seen that cones can be labeled as a datum feature in two ways (Fig. 4-3(e) and Fig. 4-45), neither of which correspond to the letter-of-the-law in para. 3.3.2.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Redundant or not? Please help

J-P, targets would be much easier, but is there anything illegal / prohibited about using the (T) modifier on a secondary or tertiary datum?  My thought is that it would not establish a specific line in space which may or may not reside on the feature, but rather one which is guaranteed to be on the feature (at least at one point or line).  Just a thought for consideration.

btw, don't recall noticing (c) on Fig. 3-4 ('09) previously. Have taught (h) & (f), though I've had people argue with me about their validity.

Also, I had mentioned the callout for cones for the very reason that J-P mentions; it sets precedence for cylinders, whether or not explicitly laid out in the text or other graphics.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: Redundant or not? Please help

The thing about "T" on datum references never occurred to me, because the very definition of establishing a datum is already based on tangent contact.   Think of a traditional flat surface datum... the simulator only feels the high points anyway (tangent plane).    You're talking about the top of a cylinder, but I would rather use targets than try to impose "T" in the datum reference portion of a feature control frame.  Shrug.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Redundant or not? Please help

Ah, but there is a distinct difference between a plane based on 3 points of contact and one based on a tangent plane mutually perpendicular to higher-precedent datums.  Anyway, it was just another item for thought.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

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