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Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
I am learning tolerance stackups and I am using Alex Kurlikovski book (Fundamentals of Geometric dimensioning and Tolerancing, 2nd edition). I have a question about the stackup tolerance calculation --fig 9-14 page 265—attached—
Minimum distance X min calculation shown is 4.5mm. Someone around here, who has way more experience than me in those kind of calculations, is claiming that the “real” X min calculation should be 4.1 (not 4.5 shown) because the form error was not included.
In the book: X min is :
69.6 (min length) – 50 (basic) - 10(basic) – 8.6/2 (max size for the hole) - (0.6+1)/2 (hole at the LMC, hole position is at MMC) = 4.5mm
Our expert is claiming the calculation should have started from 69.6 - 0.4 = 69.2 and not from 69.6. Therefore, the result would be 4.1mm and not 4.5mm.
Justification: the size of the feature (length) still has to be ±0.4mm (70.4/69.6 = 70±0.4), if the opposing points meet the size specification and the envelope meet rule#1, then the length meet the requirements. The form error was not taking in consideration for the calculation in the book. (a gage can use all 0.4mm in form error and still be making contact with the datum feature simulator)

I know pmarc had some issues with X min calculation in fig 9-12 page 263 (x min should be 2.7 and not 2.9) and here is that specific thread.
http://www.eng-tips.com/viewthread.cfm?qid=335464

And it’s exactly as pmarc stated: “It is weird to disagree with such authority”
Now, going back to our issue (page 265): Ii is our “expert” points us in a right direction or “the unclaimed form error” is not applicable here?

Thank you

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Why is he subtracting 0.4 from the 69.6? You can't do that because 69.6 is the shortest that the part can and still be good. Any form deviation can only make the part longer. Maybe I'm oversimplifying this but I'm pretty sure your expert is not correct this time. That being said, I definitely have some problems with some of AK's material and especially with the new 2009 textbook but in this case I think it's pretty straightforward. I'm looking forward to others replies.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Calculations shown in fig. 9-14 are correct, your expert is wrong. Form error has nothing to do with the stackup result in this case. Why is the expert even using 0.4 and not 0.8? After all 0.8 is the maximum form error of 69.6-70.4 width.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)

Quote (pmarc)

"Why is the expert even using 0.4 and not 0.8? After all 0.8 is the maximum form error of 69.6-70.4 width."

I guess because 69.6 is already at its min size, so you subtract only 0.4 (69.6-0.4)
Would be 0.8 if subtracted from nominal 70 (70.0-0.8)


His claim is:
“ Imagine the part has a perfect left edge (datum feature B, in the picture) meaning the surface B is perfectly perpendicular to datum feature A, then the part is at its minimum length 69.6 (let’s say on the top of the part) and the remaining (not included in 69.6) form error 0.4 would be on the bottom of the part. Therefore, the X min dimension is influenced by this form error (no orientation, perpendicularity, angularity requirement between the right edges (2 times) and datum feature A). He said it’s a very common error that the 0.8 tolerance zone for the direct toleranced dimension can move only 0.4 towards the holes related to the DRF. There are actually two tolerance zones when relating to planar features together with direct tolerance zone (± linear dimension) and both tolerance zones have a width of 0.8.”
Hmmm!! I am lost………I might need some help here

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

As pmarc said, your expert is wrong. The dimension can never be less than 69.6. The form error allowable is not 0.4, it's 0.8 so he's wrong about that too. When the part is at 69.6 the form error can only go towards MMC. The part can not be smaller than 69.6 in any place, at any time.

You are not lost, your expert is.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I guess your expert needs much more help than you do smile
Regarding form error, if left face is perfectly flat and perpendicular to A and the length of the part is 69.6 at the top, the length of the part at the bottom can be 70.4, resulting in 0.8 of both right faces form error and not 0.4.

The only problem with fig. 9-14 I have is that there are no geometric controls between datum features, so theoretically the part can be a parallelogram far different from what pictures with part installed on gage are showing.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

It looks to me that both threads are falling into the same trap: nobody knows for sure what dimension in question really is.
In older example AK was looking for “thickness”. Is thickness dimension? Is it feature of size? Is it subject to “caliper rule”?
In new problem X called “distance”. Even better. But the same questions still apply.
If X is the smallest point-to-point distance, then we have to take form error into consideration.
If X is “caliper measurement”, we can ignore form error but get different numbers on our stack-up.
Until we agree on our definitions, the whole thing looks like argument about value of 2 + 2 without knowing what “+” means.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

CH,
Why do you think that form error has to be taken into consideration in what you call point-to-point distance case? And how would it look like in stack-up in your opinion?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

AK's book is a fundamentals book. Fundamentals. With or without CHs graphic, the resident expert is incorrect in his assertion that you can legitimately subtract 0.4 from the LMC value of the part and still somehow have that dimension be compliant. I don't agree with the point you are trying to make with that graphic CH but let's try to get to the bottom of what greenimi is asking about first.

Do we all at least agree that AKs exercise is correct on a fundamental level without adding minutiae that will only serve to further confuse greenimi?

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Agreed, John. Alex did it right.

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

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I say that calculations for MIN distance are correct.

However I do not agree with calculations for MAX distance. There is no geometric control between datum features A and B defined on the print, thus the angle of surface B wrt A is not controlled at all. And since 69.6-70.4 width is, by definition, not measured in relation to the datum reference frame A|B|C, the maximum considered distance X stays uncontrolled too.

6.9 MAX is the answer only when the datum feature B is perfectly perpendicular to datum plane A.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Before we go to pmarcs’s issues about how to calculate MAX distance, I would like to ask you guys if you have some examples from Advanced or Tolerance stackup books from AK (Ref quote from powerhound).

[quote powerhound][Do we all at least agree that AKs exercise is correct on a fundamental level without adding minutiae......]

I only have Fundamental GD and T (AK) and if this example is treated as fundamental, I would like to know how the Advanced book (or the Tolerance Stackup Book) treat the same example (or maybe a similar one). Can somebody post a picture from other books which consider the stackups at more advanced level?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
I guess is the same scenario as we encountered for the composite for single surfaces callout (on the fundamental level is a No-No, but on the advanced level can be done, because the standard does not specifically forbid it).

On my stackup case, on the fundamental level, the X min calculation is okay, but on the advanced level can be different?
Maybe pmarcs’s issue with X Max Distance could be the same (on the fundamental level, the calculation is right/correct, but if we go to more advanced level X Max Distance is different and is based on other requirements (perpendicularity, angularity, form error), etc.
Again, who has some advanced stackup calculations that can be shared with others? (Alex Kurlikovski Advanced or Stackup books or any other)



Mark Foster's answer on the thread below (ref to my post --at the beginning--)
“While I know and respect Alex K's GD&T knowledge, the quote that you are using is from his Fundamentals-level text as well as his online resources. When I teach GD&T to people new to the subject, I also make a similar statement (i.e. that composite feature control frames are to be used on multiple features at a time, not just for one feature) because that IS the intent of that tool, and it is probably the best use of that tool. However, when we get into more advanced topics, we find ways to combine various tools (e.g. composite and simultaneous requirements) in ways that we may not have thought of when we were at a Fundamental-level of knowledge. The Y14.5 standard is intended to be a book full of definitions, rules, guidelines, language tools in general, that we are able to use in order to communicate effectively. So just as there are some people who just barely speak a language and there are others who have a supreme command of that language, we have to learn as we go to move from the former to the latter.”

http://www.eng-tips.com/viewthread.cfm?qid=341776

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

The example would be treated in the exact same way in an advanced concepts book.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greenimi,
There is no such thing like different stack-up results depending on different level of its complexity. Either you include all factors in the calculations or you produce worthless sheets of paper filled up with numbers.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Pmarc,
So the root cause is maybe our interpretation of the direct tolerance dimension (±) which is different than the one in the book.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

It seems that this whole thing has been made way more complicated than it has to be. I'm not getting why there's a problem with this exercise.

While the right edge of the part is not related to a DRF, the hole pattern is. It is related to the left edge (datum feature B, secondary). Since datum feature B is secondary and has to have two point contact with the simulator, the right edge, effectively, is controlled parallel to datum B within 0.8. I know this isn't a parallelism callout but my point is that the right edge is indirectly related to the DRF through its relationship to datum feature B. When this part is fully constrained within its DRF, the MIN and MAX calculations are correct. The DRF should match the function of the part so calculating MIN and MAX distances like this is really not a problem.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greenimi

I can recall pmarc gave us an excellent step by step explanation on the calculation of tolerance stack, pls see the link below.
http://www.eng-tips.com/viewthread.cfm?qid=287922

Season

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

powerhound,
Allow me to respectfully disagree with you. Please have a look to attached file.

http://files.engineering.com/getfile.aspx?folder=e...

All 3 cases show...
- width of the part at its MMC = 70.4;
- hole at its MMC = dia. 8.0;
- position tolerance at hole's MMC = dia. 1.0;
- hole shifted towards datum plane B as much as possible within defined positional tolerance...
as the prerequisites to find the maximum distance X.

I hope it also shows that the right edge does not necessarily have to be related to datum plane B within 0.8. It is all because of lack of predefined geometric relationship between datum feature A and B.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Pmarc,

May I ask why you measure distance X the way you do and call it “maximum”?

Genuinely curious

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Oh, and short addition to my previous post:
- to have a better picture I increased the thickness of the part in my graphic - it has no impact on the stack-up result;
- in cases #2 and #3 datum feature B stays in linear contact with its datum feature simulator (so at least two points of contacts exist).

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I thought we had hashed this out before: Doesn't it have something to do with how you define max and min? In other words, is the min distance the same CONSISTENT min all the way through the part? Or just the min at ONE end of the hole? I believe that this makes a difference in how we are all approaching the question.

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

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

You are right, CH. I attached dimension to wrong end of the right face. But I think that doesn't change anything in my reply. My apologies.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

pmarc, I wasn't thinking about it that way. Somehow, your explanation wasn't clear to me either. The graphic worked perfectly though. I see what you're saying now.

Still though, I don't think this detail should be brought up in the context of the OP. It only serves to confuse the issue as evidenced by greenimi's subsequent questions regarding differences in the fundamentals and advanced concepts. Regardless, greenimi's expert was not correct in how he was calculating the distance.

Thanks for clearing it up for me.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)

Quote (SeasonLee):

I can recall pmarc gave us an excellent step by step explanation on the calculation of tolerance stack, pls see the link below.
http://www.eng-tips.com/viewthread.cfm?qid=287922

Season,
I know pmarc's stackup calculation. However, I think it does not fit very well my case because pmarc's case HAS an orientation control of the right edge to datum feature A and the datum feature B---perpendicularity 0.1 A primary and B secondary. This perpendicularity also control the form error in pmarc's case. In my case (AK Book) that control (orientation control) does not exist so the form error is controlled by the rule#1, right? And here we got that issue, on how that form error is included in the stackup calculation.


Quote (J-P Belanger ):

In other words, is the min distance the same CONSISTENT min all the way through the part? Or just the min at ONE end of the hole? I believe that this makes a difference in how we are all approaching the question.

J-P
No, the X min distance is NOT consistent (at leat in our opinion) all the way through the part.
Okay, let's say in AK book is consistent, because is a Fundamentals Book.
But, I would like to ask you guys, how the calculations would be different (exactly as J-P stated above) if the X min distance is NOT cosistent through the part and how the form error (indused by the direct toleranced dimension ± --70±0.4---) shoud be taken in consideration. That I need the help for.  
Thank you gentlemen

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
After re-reading pmarc’s replay for the form error I have to agree that the maximum form error in this case is 0.8.
So, I want to ask pmarc a quick question: if the part is at its minimum length 69.6, why the maximum form error of 0.8 cannot be applied from 69.6 in the opposite direction than the direction you’ve indicated. In other words, what paragraph of Y14.5 standard states that on the top of the part cannot be 69.6 at any cross section but on the bottom cannot be 69.6-0.8= 68.8.

[quote pmarc][If left face is perfectly flat and perpendicular to A and the length of the part is 69.6 at the top, the length of the part at the bottom can be 70.4, resulting in 0.8 of both right faces form error and not 0.4.”]

Why the length at the bottom cannot be 68.8? (keep the same form error, but the opposite direction). Reason the measured value of any individual distance at any cross section of a feature of size is still 69.6 (measured at the top) and the rule#1 is still in place and clearly defines an envelope of 70.4 width that the feature of size must pass through.

What am I missing here? What paragraph of the standard is violated by this approach? I know something is not quite right, but At this point and with my limited knowledge I don’t know what?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Quote (greenimi)

So, I want to ask pmarc a quick question: if the part is at its minimum length 69.6, why the maximum form error of 0.8 cannot be applied from 69.6 in the opposite direction than the direction you’ve indicated. In other words, what paragraph of Y14.5 standard states that on the top of the part cannot be 69.6 at any cross section but on the bottom cannot be 69.6-0.8= 68.8.

Unless I am reading your question incorrectly, 68.8 is not acceptable because this would simply violate lower limit of size for the width (69.6).

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Pmarc,
Our expert’s understanding (the one which is driving the stackup debate) is that there are actually two tolerance zones when relating to planar features together with a direct tolerance dimension ± and both tolerance zones have a width of 0.8.
Each portion of the left and right faces/edges of the part must fall within two parallel planes that are located 69.6 and 70.4 from tangent plane constructed by the highest points of the opposite face of the part.

He thinks that as long as you can measure 69.6 (minimum dimension acceptable) at any cross section of the feature—take subsequent measurements of the top dimension along the width 50.4/49.6 of the part—then the measured value is in tolerance—

So, if in the top (again on each cross section) you are within 70.4 - 69.6 the bottom should then be in the form error tolernace (form error 0.8 then the minimum dimension on the bottom 68.8)



1.3.54 Size, Actual Local
size, actual local: the measured value of any individual
distance at any cross section of a feature of size. See
Fig. 1-1.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
By the way, can you recommend me some good threads on this website (or any other sites) where this issue with ± direct tolerance dimension and form error has been discussed?
Thank you pmarc

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greenimi,
I think it would be much easier (at least for me), if you prepared a sketch showing the width satisfing 69.6-70.4 actual local size reuirement and in the same having 68.8 somewhere.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
The sketch attached has 3 pages
I was trying to make a 3D sketch for better understanding
10mm part thickness does not matter for this form error issue and also, I think does not matter for the final result of the stackup
Please let me know your thoughts

What am I missing ? Where am I wrong or what's not quite right in the whole matter/topic?

Also, please do not forget about some good references (other threads, websites) for this discussion.
Thank you pmarc

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

No. This is just wrong. You cannot violate the MMC or LMC boundary. If the dimension is 69.6, you can only have form error that moves towards MMC.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Greenimi, I'm with Powerhound.

Per the ASME rules, every size dimension must pass both the "actual mating envelope" and also the "actual local size." Your expert seems to be forgetting that second part! There is no way that any point across that block can be 68.8 and be acceptable.
(There are exceptions to the ASME rule such as non-rigid parts, but we're not dealing with that here.)

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

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greenimi,
I can just repeat after powerhound and J-P. The geometry shown on your pictures simply does not fall within 69.6-70.4 limits of size.

However, I have been thinking and thinking about the statement... :

Quote (greenimi):

Our expert's understanding (the one which is driving the stackup debate) is that there are actually two tolerance zones when relating to planar features together with a direct tolerance dimension ± and both tolerance zones have a width of 0.8.
Each portion of the left and right faces/edges of the part must fall within two parallel planes that are located 69.6 and 70.4 from tangent plane constructed by the highest points of the opposite face of the part.
...and I think I understand what the expert is talking about. This however does not change my standpoint that form tolerance for 69.6-70.4 width has no impact on MIN (and MAX) result of the stackup.

Here is another graphic showing (at least I hope so) why 68.8 should not appear in the calculations:

http://files.engineering.com/getfile.aspx?folder=92b17e2d-6de4-439b-897d-189e694493c1&file=stackup.pdf

So concluding all the considerations regarding MIN and MAX calculations shown in Alex's book, my statement is:
- MIN=4.5 - calculated correctly;
- MAX=6.9 - calculated correctly ONLY IF there is a perfect orientation between datum features A and B when the datum feature B is at its MMC=70.4. As I was trying to point out, the drawing does not tell this, thus the 6.9 is not the absolute maximum that can occur in as-produced geometry.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Pmarc,
You are right and you convinced us.
I would like to ask you, if the "X min" dimension would be different if "X" is the distance between datum B and the left hole?
In other words if the feature we are measuring the minimum distance from is a datum feature, is the X min calculated distance different versus the original X min shown in the book?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

If I understood you correctly, you would face with the same problem like for Xmax in the original stackup - that is, lack of orientation tolerance on datum feature B wrt A would make the stackup impossible to complete in 100%. If, however, you had this orientation tolerance specified on the print, it would be similar to the scenario I created in the presentation already mentioned by SeasonLee.
http://files.engineering.com/getfile.aspx?folder=e...

Did I get your question right?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Pmarc,

Yes, I forgot about that stackup calculation you provided awhile ago and was mentioned by SeasonLee. In that calculation you have an orientation control and the tolerance for the orientation is included in the stackup. Now, this perpendicularity control (in your example) is 0.1, so is smaller than the form error of 60.3-59.7 = 0.6. A warm-up question for you: the perpendicularity tolerance must be smaller than the form error or not? In other words can the perpendicularity tolerance be bigger than 0.6 (again in your stackup example)

And to expand a little bit:

I am questioning what’s happened if no orientation control is provided (as it is in AK book example). Why you said the stackup is impossible to complete 100% (“lack of orientation tolerance on datum feature B wrt A would make the stackup impossible to complete in 100%.”) Why we cannot use the maximum form error of 0.8 (again in AK example) to be included in the stackup ?

Also, can you verify a little bit that 7.986 (page 3 and Case#3 in your sketch) dimension. I did the same construction on my Cad system and I got for X max 7.7 (and not 7.986). But, I have used 0.8 max form error to get to my X max of 7.7. And by the way, if you said it’s impossible to calculate/complete 100%, then how you get to 7.986 –your result---what assumptions did you use—since the lack of orientation control?
The link to your stackup (for X max) is below, just for your reference.

Thank you pmarc

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Quote (greenimi)

In that calculation you have an orientation control and the tolerance for the orientation is included in the stackup. Now, this perpendicularity control (in your example) is 0.1, so is smaller than the form error of 60.3-59.7 = 0.6. A warm-up question for you: the perpendicularity tolerance must be smaller than the form error or not? In other words can the perpendicularity tolerance be bigger than 0.6 (again in your stackup example)

The perpendicularity tolerance value can be greater than size tolerance (form error).

Let's focus on my example for a moment and assume that perpendicularity tolerance wrt A|B on datum feature C is 1.0, and not 0.1. Imagine first that datum feature C is perfectly flat. In such case whole allowable form error = 0.6 is "moved" to the opposite (top) face and the maximum orientation error of datum feature C to A|B can be 1.0. Now, since nothing is perfect, picture that actual form error of datum feature C is for example 0.2. What does it mean? It just means that maximum allowable perpendicularity error of the datum feature C to A|B is reduced to 0.8 (1.0-0.2). And by analogy, for actual form error of datum feature C = 0.6 (maximum possible), the maximum perpendicularity error will be reduced to 0.4 = 1.0-0.6.

So, to conclude shortly, the drawing can specify the perpendiculariy tolerance greater than the size tolerance. It is just that actual allowable errors of form and perpendicularity for this type of geometry are dependent on each other.
----

Quote (greenimi)

I am questioning what’s happened if no orientation control is provided (as it is in AK book example). Why you said the stackup is impossible to complete 100% (“lack of orientation tolerance on datum feature B wrt A would make the stackup impossible to complete in 100%.”) Why we cannot use the maximum form error of 0.8 (again in AK example) to be included in the stackup?

I think what I said above, explains this. Doesn't it?
----

Quote (greenimi)

Also, can you verify a little bit that 7.986 (page 3 and Case#3 in your sketch) dimension. I did the same construction on my Cad system and I got for X max 7.7 (and not 7.986). But, I have used 0.8 max form error to get to my X max of 7.7.

Again, you are sticked to the belief that the maximum orientation error is limited by the maximum form error, which is not correct. Additionally, notice that in my graphic I played with angles (90, 85, 80 degress). Most likely, if I played with linear distances and assumed 0.8 in one of my sketches, I would get the 7.7. But that does not mean I could not assume 1.0 or 2.0 for instance in other scenarios.
----

Quote (greenimi)

And by the way, if you said it’s impossible to calculate/complete 100%, then how you get to 7.986 –your result---what assumptions did you use—since the lack of orientation control?

This is not the absolute maximum that can be obtained. This number is for 80 degrees angle between datum feature B and datum plane A. If I showed additional page with the geometry at 75 deg angle, the result would be greater than 7.986. Actually, in the absence of the orientation tolerance between A and B, my graphic could be showing 10 deg angle between A and B and it would not be violating the print in Alex's book in any way.

Did it help?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greenimi,
After re-reading first part of my last reply about relationship between size tolerance and perpendicularity tolerance, I am more than sure that it caused a serious confusion. Therefore I am attaching another graphic in which I am trying to explain why the perpendicularity tolerance can be greater than size (and form) tolerance.

http://files.engineering.com/getfile.aspx?folder=8...

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Shouldn't your perpendicularity be refinement of size tolerance?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

CH,
Right face on both pictures on the second page of my graphic is not the right face of the part (notice thickness to length proportion). I should have probably used thin wavy line in order not to mislead anyone.

That said, on the lower picture on page 2 for instance, the right face of the part will be most likely inclined to datum plane A at the similar angle as flatness tolerance zone to satisfy the size requirement.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Pmarc,

I am still digesting…… reading, re-reading, thinking of your last 2-3 posts (I am not very sure I am still capable of comprehending today, but the weekend is coming so…I have time to do it)
But, anyway…. Hmmm: are you saying that the sketch attached still not violating the AK book (sketch constructed to get the X max: 70.4 max size, 60 basic becomes 59.5, hole at MMC: 8.00) with 10° angle as you suggested in your earlier post. As you can see I got 26.9 max, but is also thickness dependent.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Wavy line or not wavy line it doesn’t matter.

Orientation is always refinement of the size.

See ASME Y14.5-2009 Fig. 6-2 for example. “The surface must be within the specified limits of size”

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greeimi,
In general the part could look like this, with one remark however -- 70.4 dimension should not be measured in a way you are showing it. It is a distance between two inclined parallel lines, not the distance measured in a direction normal to datum plane B.

CH,
I fully agree with fig. 6-2, but it is not what we are talking about here. We are not debating on orientational relationship between left and right face (that is two nominally parallel surfaces) of the part in my and Alex's example.

BTW, could you point me to a place in the standard where it is really stated that ORIENTATION tolerances must be a refinement of the size. From what I see such statement exists only for PARALLELISM tolerance.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

First of all, there is no difference between parallelism and perpendicularity. Both are angularity with different value of an angle.
I know “math” is 4-letter word on this forum, but I still have to say they are mathematically equivalent.
(It isn’t only me who says it, Y14-5.1M does too)
Now, will somebody please explain the difference between two cases shown on the picture?
In both cases tolerance zone is trapped between 2 parallel planes oriented in space the same way.
Why in one case this zone is allowed to exceed size limits and in another is not?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

If you need exact legalese saying there is no difference between parallelism and perpendicularity, see Para.6.6 ALTERNATIVE PRACTICE.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

What makes you think you can measure size in random arbitrary direction?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Well, I can't find proper text '09 edition of the standard, but in '94 you can find a note at the end of para. 4.4 saying that in order to relate linear or angular dimensions to a datum reference frame an explicit note must be placed on a drawing. To me this means that as long as there is no such note, the dimensions are not related to datums and shall be measured independently of the datum reference frame.

I am pretty sure that in A. Krulikowski's GD&T Fundamentals there is a figure showing this, but in the light of what I have been trying to do throughout the whole thread, using his book as a reference may sound at least funny.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

It’s funny, but now I start agreeing with you.
2009 doesn’t add clarity, especially if you look, say, at Para.1.9.1 Rectangular Coordinate Dimensioning referencing Fig. 1-49.
Dimensions on the left picture do not only “locate features”, but definitely create size (same with Para.1.9.2/Fig. 1-50).
Then does the rule “linear dimensions specify distances in coordinate directions from two or three mutually perpendicular planes” apply to the sizes (like 45 and 90 on Fig. 1-50) as well?
One may only guess sad

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I am glad that we start agreeing on something.

I do not want to sidetrack the discussion, but my general comment about chapter 1 to any reader would be - please be careful, the chapter just shows some general techniques of dimensioning, not how to make proper tolerancing.

And coming back to our main topic on perpendicularity tolerance value vs. size tolerance value, does it mean that you have been convinced that perpendicularity tolerance can be greater than the size tolerance? (I am not asking you just to make me feel better. I think greenimi has not been convinced yet and needs additional votes on this). And going further, does it also mean that in the absence of perpendicularity control between A and B in Alex's example, you would agree that the MAX value in the stack-up can't be properly calculated?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I mostly agree that unlike edges and axis standard isn’t clear about interpretation of dimensions being parallel and perpendicular to each other.
I am quite sure that in example from AK’s book ALL and not only basic dimensions are aligned with DRF and the whole problem is simpler than we think.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

SeasonLee,
Since the first picture in this thread was taken from one of previous editions of AK's GD&T Fundamentals (based on Y14.5M-1994), I am curious whether similar exercise is shown in the newer edition of the book (based on Y14.5-2009). Could you please check?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I really don’t think it’s from Fundamentals.
It’s from Advanced, or separate book on Stack-up.
It just cannot be from the same book OP example is taken from.
Dimension C is clearly aligned with the DRF, so form error is definitely not considered.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

It is from Fundamentals - I have this book in front of me.
While the stackup calculations indeed show "Max width dimension from datum B", as you underlined, the drawing at the top does not specify this is the way the 69.6-70.4 dimension should be interpreted.

Imagine one has to do this stackup (or similar) on his own without looking at this example. What makes you think that the interpretation of 69.6-70.4 dimension will be in line with AK's interpretation?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

What year is your “Fundamentals”? My only has Fig. 9-14, but not Fig. 13-17.

Quote (pmarc)

While the stackup calculations indeed show "Max width dimension from datum B", as you underlined, the drawing at the top does not specify this is the way the 69.6-70.4 dimension should be interpreted

You cannot be serious. If max dim is measured from datum and equals 70.4 and min dimension is measured from datum and equals 69.6, then how else they are interpreted?

When one has to do stackup on his own without looking at the example one is free to cut the corners as one pleases.

The only thing I am certain – I am even bigger fan of Independence – just to know for sure NOTHING is related unless said otherwise.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Quote:

What year is your “Fundamentals”? My only has Fig. 9-14, but not Fig. 13-17.
I was talking about fig. 9-14 (the very first picture in this thread) and not 13-17, which is probably taken from a newer edition. Since SeasonLee posted 13-17, I thought he could search in this edition for an example similar, or better yet, identical with 9-14.


Quote:

You cannot be serious. If max dim is measured from datum and equals 70.4 and min dimension is measured from datum and equals 69.6, then how else they are interpreted?
You know min and max are measured from datum, because the answer says so. The print is not.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Quote (pmarc)

You know min and max are measured from datum, because the answer says so. The print is not.

The question is WHY the answer says so? Because "one" can simplify his/her work the way one sees fit.
This is what I said in my very first post on this thread: if you don't agree on your assumptions you cannot agree on your results.

I hope you agree that it's really sad state of affairs, if Fig.9-14 is the only example of stackup available to the users of Fundamentals.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

pmarc

The picture attached is from the latest textbook (2009) chapter 13 page 165.

Season

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Thanks, SeasonLee.
Is a stackup similar or identical with 9-14 shown in this textbook?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

pmarc

I can't find out the similar example (as posted by OP) in the 2009 textbook.

Season

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

pmarc

Sorry for the confusion, the attached picture in chapter 13 is the picture of datum related dimension vs non-datum related dimension.

You asked a good question, why it disappeared in the 2009 textbook?

Season

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Just to confirm (if it’s still necessary, but I think pmarc already cover it) the original OP picture fig. 9-14 is taken from AK Fundamentals (based on 1994 standard).
I understand that the calculation in the book for X min is correct (with the assumptions covered throughout the thread, such as min width dimension from datum plane B). The same thing for X max (with the suppositions presented by pmarc—perfect orientation between datum features A and B when datum feature B is at its MMC). Just want to be clear: I understand that.
Now, I would like to extend a little bit the discussion about how 70.4/69.6 (direct tolerance dimension) is supposed to be measured. Why I am questioning this? Because, I think a couple of replies ago, someone made the statement that “how you define max and min dimensions” makes the whole difference in the world in how we are all approaching the issue. In other words, let’s say the min distance is NOT the same consistent min all the way thought the part and we are interested to find the “ABSOLUTE” min at one end of the hole (more or less like a minimum wall condition).
How the calculations are done in this case? There is any difference?
Also, I would like to ask, how “the actual local size” is supposed to be measured? ( Yes, I know, we missed this “actual local size” initially and pmarc had to spend time convincing us about that requirement, and he did that successfully)
Therefore:
What means “the measured value of any individual distance at any cross section of a feature of size”?
What is the direction of measurement for the local size?

Y14.5-2009
2.7 LIMITS OF SIZE
Unless otherwise specified, the limits of size of a feature
prescribe the extent within which variations of geometric
form, as well as size, are allowed. This control
applies solely to individual regular features of size as defined in para. 1.3.32.1. The actual local size of an individual feature at each cross section shall be within the specified tolerance of size.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greenimi,
The definition of actual local size as defined in '09 edition of Y14.5 is... how to say it as gently as possible?... unclear. I mentioned about this in my thread about shortcomings of Y14.5-2009. http://www.eng-tips.com/viewthread.cfm?qid=342749

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
pmarc,
Thank you.
I will take a look. I also have seen another thread where your statement is:

"While it looks like the easiest way of defining size (length) of the pin, it can easily turn into real can of worms when one wants to analyze direction in which measurements for that size should be taken. It is all because neither Y14.5-2009 nor associated math standard Y14.5.1-1994(R2012) give unambiguous definition of what actual local two-point size is and how it should be determined. Saying that actual local size is "the measured value of any individual distance at any cross section of a feature of size" is so muddy, that I am pretty sure there is no muddier definition in the whole standard."
16 Jun 13 8:31

http://www.eng-tips.com/viewthread.cfm?qid=346732


I found it after I have posted the questions in my previous post




RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

(OP)
Pmarc,
I found a book written by Louis Gray Lamit, and the local size definition is….well as shown in the attachment.

I know, it’s the author interpretation of the standard , but …. isn’t it confusing that on page 614, the LMC measurement is shown to be perpendicular / normal to the axis (see the 90° corner shown) and on the next page 615 fig g the LMC is ALSO shown diagonal (between the two radiuses).? Does the LMC also applies to the bottom of those 2 radii? LMC is the minimum distance between the semicircular areas?
Am I missing somethig?
Thank you

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I think author took "caliper rule" way too seriously. Can your LMC dimension be actually larger than your MMC dimension?

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

Poor definition in the standard = different, sometimes surprising, interpretations of this definition.

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

greenimi

Would you please provide page 613 (or page 612) to see what author said on that figure.

Season

RE: Tolerance stackup calculation (ref pmarc example Alex Kurlikovski Fundamentals GD and T book)

I can’t find out author’s comments on that particular Fig.16-38 (g), agreed its easy makes reader confused.

Season

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