Stackup -comparison

[greenimi]

Question for the group":
(Ref: ""maximum wall thickness at one spot" vs. "maximum consistent wall thickness." from a previous discussion)

How the stackup -minimum and maximum wall distance- change (if it does ) , IF I would say that:

X maximum = maximum possible distance that can ever happen in a single cross section for cases.
x minimum = minimum possible distance that can ever happen in a single cross section for cases.

Will those two values of 2.35 and 0.65 for the maximum wall distance and minimum wall distance respectively, change with my above adjustment?
If yes, what would be the "new" values for X maximum and x minimum?

Thank you very much

 

[greenimi]

Let me turn it back to you... Is the Krulikowski answer for Xmin flat-out wrong?

No. It is not wrong, but in the AK book the case shown is "the consistent thickness case".
The case depicted by pmarc's calculations is "the thickness at one spot case".

Regardless of which case you choose MMB or RMB on datum feature A will bring the same results when X maximum and x minimum are calculated.

"the thickness at one spot case" is:

X maximum = maximum possible distance that can ever happen in a single cross section for cases.
x minimum = minimum possible distance that can ever happen in a single cross section for cases.

Again, to rephrase, this is what I understood from other discussions here on eng-tips.
I have concluded that is those "simple" calculations MMB or RMB on datum feature will "produce" exactly the same results.
Do not try to extrapolate to anything else more complex that this.

Please correct me where I am wrong.

 

[Belanger]

Well, it seems that we were using the terms differently all along. Pmarc's picture was not what I was envisioning as "one-spot" thickness. My use of the term involves the depth factor of the cylindrical part -- maintaining the same thin-wall condition throughout the depth of the hole.

AK's example is not what I would call the consistent wall thickness, because his Xmin still only occurs at one clocking location around the circular part. It sounds like your use of consistent wall thickness can only happen if both diameters are perfectly round, and the location between the two axes is perfect.

 

[Belanger]

Just to clarify what I meant by "thickness at one spot"...

 

[greenimi]

Lets clarify this: I am now confused myself.

Pmarc,
I agree with your calculations, but some clarification is still needed.
Which case your calculation covers? consistent thickness case or thickness at one spot case:

Where [highlight #4E9A06]thickness at one spot case[/highlight] is:
X maximum = maximum possible distance that can ever happen in a single cross section for cases.
x minimum = minimum possible distance that can ever happen in a single cross section for cases.

Do you agree with these statements I made few days ago? I am ready to stand corrected, but those are my understanding as per TODAY (reading and re-reading other threads here on eng tips)

if the asked question is: what is the X max and X min in the consistent thickness case: I would say that the answer X max: 2.35 x min:0.65. No matter if a is MMB or a is RMB those answers would not change.

if the asked question is: what is the X max and X min in the thickness at one spot case: I would say that the answer X max: 2.35 x min:0.45. No matter if a is MMB or a is RMB those answers would not change.

 

[Belanger]

greenimi -- I'm really interested in hearing your definition of one-spot thickness (maybe post a sketch?). I showed that I'm seeing it as a 3-D concept, but I think you're seeing it in a 2-D cross section?
Please elaborate; I can't follow the math unless I know what exactly your term is trying to get at.

 

[pmarc]

grenimi,

My example shows an as-produced part that has consistent Xmin and Xmax along its whole length. You decide which of the two definitions it fits the best.

 

[greenimi]

pmarc and J-P,

Sorry for the delay, I had a couple of days off.
Here it is a picture from a training material I got few years ago.

You can see there, is shown the difference between "thin wall" 11.07 and "min wall" 11.04.
Per my understanding, this is the difference between consistent thickness case 0.45 and consistent thickness case 0.65

Based on my latest sketches, do you agree that if datum feature C is changed at MMB -- C(M) -- those two values (11.07 and 11.04) will NOT change?
Please let me know, what do you think. If the values will change, then why ?

 

[Belanger]

Yes, that's pretty much the same idea that pmarc was showing (which I agreed with). I just disagreed with your usage of the terms consistent vs. one-spot. Recall that your initial question in this thread was asking about "maximum (and minimum) possible distance that can ever happen in a single cross section." Given your latest pictures, I would agree that the minimum is the picture on the right (11.04). I was seeing that minimum as "consistent" throughout the depth of the feature.

I guess that's where we diverged in our terms. Now look at my hand sketch from July 24; I was envisioning even more reduction in the minimum if we also consider any depth-wise tilt of the hole. So I apologize for muddling the terms... you brought up a good point about the original Krulikowski calculation, and from there I went down a different road with the one-spot thinking.

 

[Tarator]

Assuming it is a rigid and non-stock part, is there any difference between the two drawings below? To me, they are identical. So the OB should be 17.62 for both. But based on the Y14.5 standard, OB = 17.56 (left), and OB = 17.62 (right). Am I correct? If so, I think maybe ASME should consider changing the definitions for LMB for size tolerances with no geometric tolerance where Rule #1 applies.

Also, maybe the new Measurement Data Reporting standard can formulate this, so it is measured. What I mean is, if you have 3 ballons, you would only have 3 line items in your stack-up (let's say, you wanted to know the minimum thickness in a measured part, and you wanted to put in the measured values).

 

[greenimi]

But based on the Y14.5 standard, OB = 17.56 (left), and OB = 17.62 (right).

For what I know the LMB for both drawings posted (Drawing #1 and Drawing #2) is 17.62.

 

[greenimi]

Just to justify my previous post, I would ask what is the size boundary (LMB) shown in the embedded picture--between those two red arrows?
Isn't it: 20.2 + 0.1 (20.3) ?
If not, why not? Then what it is?

 

[greenimi]

So, where we are here?
Do you guys agree that C(MMB) or C(RMB) (or A(MMB) versus A(RMB) for the other picture) will not change the min. wall regardless how the thickness is defined?