Can indirect control override direct one?
Can indirect control override direct one?
(OP)
There was very heated exchange recently on this forum caused by ambiguous understanding of some standard terminology. Unfortunately, most participants concentrated on emotional part of the discussion, and overlooked serious underlying problems.
Here I have no intention to start another fight, but rather try to figure out if it is possible to find some common understanding in the realm of “default”, “specified otherwise”, “direct”, “indirect”, etc.
Imagine that we have drawing of a part, that has cylindrical feature. Let’s call that feature “X”.
The drawing title block has a requirement: “UNLESS OTHERWISE SPECIFIED, MAX ROUNDNESS ERROR IS 0.05”
There is also direct 0.10 Runout control applied to feature “X” via FCF.
As we all know, Runout indirectly controls Roundness. Armed with that knowledge, please answer the following question:
What is the maximum allowed Roundness error of feature “X”?
a) 0.05
b) 0.10
c) None of the above (please explain)
Thank you in advance for your opinions.
Here I have no intention to start another fight, but rather try to figure out if it is possible to find some common understanding in the realm of “default”, “specified otherwise”, “direct”, “indirect”, etc.
Imagine that we have drawing of a part, that has cylindrical feature. Let’s call that feature “X”.
The drawing title block has a requirement: “UNLESS OTHERWISE SPECIFIED, MAX ROUNDNESS ERROR IS 0.05”
There is also direct 0.10 Runout control applied to feature “X” via FCF.
As we all know, Runout indirectly controls Roundness. Armed with that knowledge, please answer the following question:
What is the maximum allowed Roundness error of feature “X”?
a) 0.05
b) 0.10
c) None of the above (please explain)
Thank you in advance for your opinions.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future





RE: Can indirect control override direct one?
Roundness is form only so the axis it is compared to is its own... I choose a) 0.05
I would re-word the comment "As we all know, Runout indirectly controls Roundness." Since a perfect roundness can have a imperfect runout since it may be compared to an axis not its own I would say that roundness influences runout.
Paul
RE: Can indirect control override direct one?
RE: Can indirect control override direct one?
I think the title block requirement will always apply unless the feature has a directly applied roundness roundness requirement with a larger tolerance value, or a note such as "TITLE BLOCK ROUNDNESS REQUIREMENT DOES NOT APPLY TO THIS FEATURE".
pylfrm
RE: Can indirect control override direct one?
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Can indirect control override direct one?
RE: Can indirect control override direct one?
Total runout controls form and location. The entire feature must be contained within two coaxial cylinders 0.10 apart and coaxial with datum (whatever that is). These two cylinders have no size limits, except they
must be contained within the limits of size.
The feature can have poor form of up to 0.10 (effectively controlling cylindricity), OR poor location of up to 0.10 (effectively controlling position regardless of feature size (RFS)), OR a combination of both adding up to 0.10 (say, 0.05 cylindricity and 0.05 location)
This means that if part satisfies 0.10 Runout it always automatically satisfies 0.10 Cylindricity. This is what people mean when they say “Runout indirectly controls Cylindricity”. Sometimes they also say that Cylindricity refines Runout. Both terms are not really strongly defined, which is the reason for confusion.
@3DDave: I would greatly appreciate if you find the reference to back your statement. That will make life simpler for all of us.
So far I see that most people leaning towards the idea that default 0.05 Cylindrisity and explicit 0.10 Runout are not in conflict with each other. Will wait for opinions from the "experts".
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
Since some answers to your question have been given allow me to modify your question a little bit.
Imagine that we have drawing of a part, that has let's say 5 coaxial cylindrical features. Let’s call one of the features “X”.
The drawing title block has a requirement: “UNLESS OTHERWISE SPECIFIED, MAX ROUNDNESS ERROR IS 0.05”
There is also direct 0.10 Runout control applied to feature “X” via FCF.
Size tolerance (total) for the diameter of feature "X" is 0.02.
As we all know, both Runout and Size tolerance are able to indirectly control Roundness. Armed with that knowledge, please answer the following question:
What is the maximum allowed Roundness error of feature “X”?
a) 0.02
b) 0.05
c) 0.10
d) None of the above
Could you, or anyone else, answer this question?
Thank you.
RE: Can indirect control override direct one?
What I can't unsee is yet one more drafter who did not comprehend the difference between runout and circularity. Usually it takes the form of a drafter specifying roundness or concentricity when he means runout. This time, we have this mess.
RE: Can indirect control override direct one?
Is this a trap? Smell like one
RE: Can indirect control override direct one?
John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
RE: Can indirect control override direct one?
This is not a trap. By asking my question, I am just trying to answer CH's question from the title of this thread.
RE: Can indirect control override direct one?
Do you have answer to the original question yet?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
0.02 on pmarc question( something else is "indirect" /implied specified for circularity and make it 0.02).
I know, I am guilty using the "double standard"
I also know pmarc is right of reading the note as unless othwerwise specified ...and something else IS specified (the runout)then the circularity should be controlled by the runout and not by the default condition.
If I would be in manufacturing I would go by pmarc interpretation. Since I am in design, I would go by CH interpretation
Crazy rule#1 is the main culprit.
RE: Can indirect control override direct one?
You have a spec. It must be measured or verified. Measuring something similar does not recuse you from meeting the spec. Unless you have a mathematical path that leads from runout measurement to max roundness error (and you don't), then you're not off the hook.
I don't make the rules. I don't really enforce them most of the time. But I do understand them.
It's overdimensioned. Should be fixed. Get a deviation and request a change.
RE: Can indirect control override direct one?
Is is a hypothetical example. No deviation needed. Nothing needed to be fixed.
RE: Can indirect control override direct one?
RE: Can indirect control override direct one?
I don't think so. Neither one.
RE: Can indirect control override direct one?
chickened outcarefully avoided answering simple straightforward question, I will have to do it myself.Answer to pmarc's question is...
a) 0.02
And by that I mean "limits of size control the circularity" (thank you, powerhound) because I don't know if it's +/-0.02 or total 0.02
Now what?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
pmarc was clear on size tolerance---see his orginal posting
"Size tolerance (total) for the diameter of feature "X" is 0.02."
RE: Can indirect control override direct one?
O, I am pefectly fine "off the hook"
Simple fact that RUNOUT = CYLINDRICITY + SOMETHING_ELSE, and SOMETHING_ELSE is not zero, is mathematical proof that runout measurement of 0.10 always satisfies cylindricity requirement of 0.10
The same way, PARALLELISM measurement of 0.10 guarantees that flatness requirement of 0.10 is satisfied.
RE: Can indirect control override direct one?
It wasn't me who called the question "a trap". Just trying to protect myself
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
My answer to this one is - impossible to say because we do not know what the total size tolerance for the diameter of feature "X" is.
- Assuming you added the missing info to the question, and the total size tolerance is less than 0.05, then my answer would be "c) None of the above".
- Assuming the total size tolerance is equal to 0.05, then we actually have nothing to discuss and the answer has to be "a) 0.05".
- Assuming the total size tolerance is greater than 0.05 but less than 0.10, say 0.08, then we are back in the previous "heated" thread where we tried (at least I hope we tried) to solve the dillemma whether size tolerance, as an indirect control of parallelism, is or is not able to override the UOS parallelism requirement given in the title block. In this case there will be a question whether size tolerance, as an indirect control of roundness, is or is not able to override the UOS roundness requirement given in the title block.
- Assuming the total size tolerance is greater than or equal to 0.10, say 0.15, then we are again back in the previous thread, but this time we have to solve the dillemma whether runout tolerance, as an indirect control of roundness, is or is not able to override the UOS roundness requirement given in the title block.
And regarding the 3rd and 4th bullets, if I did not make myself clear enough in the previous thread, I will try now.
I do understand why most people think the correct answer would be "a) 0.05" in both cases. But I also see why someone may say: "I disagree, it is 0.08 in the 3rd and 0.10 in the 4th. If in certain cases direct roundness tolerance from the title block can be overriden by indirect roundness control, then why couldn't it be overriden in all other cases?" If the answer to that is: "It can't, because roundness tolerance from the title block (0.05) is lesser than the indirect tolerance value", then another question is: "Can you prove that my thinking is incorrect?"
This is what I have been missing in this entire debate (both threads) so far, CH. You have not proven that the thinking other than yours is incorrect. Or in other words, you have not proven that your and only your interpretation is the correct one.
If I could summarize this discussion really shortly, in my opinion one of the most important takeaways from it is that the UOS notes must be used wisely. It is not that they should not be used at all. In some cases they can do really great job, but sometimes they may get us into serious unexpected troubles.
RE: Can indirect control override direct one?
Were this a real situation I'd suggest the drawing creator not wimp out and they go back and apply the controls to the features the way the standard says to. And then I'd probably select 0.05, unless the size tolerance was smaller or some other control was also applied.
The problem with the UOS version is that there isn't a good way to determine what factors override UOS application - is it when an explicit control is looser or tighter and does that include the size tolerance? Perhaps the note could be expanded to include those conditions, but then it's back to -why?- when a perfectly good standard is sitting nearby with examples.
RE: Can indirect control override direct one?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Can indirect control override direct one?
I'll answer "a) 0.02" for your modified question. However, I would not consider the 0.05 roundness tolerance to be overridden. I'd say all three tolerances apply.
I agree with the main takeaway that UOS should be used carefully. Perhaps alternate wordings should be considered. While not a drop-in replacement, "UNLESS SPECIFICALLY EXEMPTED" might be useful in some cases.
3DDave,
pylfrm
RE: Can indirect control override direct one?
Just follow me here:
UOS MAX ROUNDNESS ERROR IS 0.05 = Default requirement
MAX DIMENSIONAL ERROR IS 0.02 = Default requirement fulfilled (or you can call it “satisfied”, or whatever). Roundness cannot exceed 0.02 falls under "Roundness cannot exceed 0.05"
MAX RUNOUT ERROR IS 0.10 = Default requirement is fulfilled (There is NO conflict between default and local requirement. If we agree that runout is compound control, and form and location are two major contributing factors, we simply clarify that remaining 0.05 error may be attributed to locational error)
@Belanger:
Many of these comments would have been different if “experts” like yourself responded with opinions on the problem on hand, rather than personalities of the posters.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
Let say, MAX DIMENSIONAL ERROR IS 0.15 and Rule 1 is in action.
Rule 1 is compound control in some way similar to runout as I described it before. The total tolerance value is distributed between local size and form errors. How exactly is it distributed? THERE IS NO RULE. Nowhere in the standard it says how to split the value between the two. Pmarc believes that it's my burden to proof that something doesn't exist. Sorry, this is not how it works.
Roundness (cylindricity) is a refinement of Size tolerance - that's a fact. 0.05 is a refinement of 0.10, 0.15, 1.00, whatever.
Now I would like pmarc to show that somethig DOES exist: would you please show us the rule that states, that increase in dimensional tolerance must result in increase in associated roundness?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
Let's throw runout out of the window.
Case 1:
UOS MAX ROUNDNESS ERROR STILL IS 0.05 = Default requirement
MAX DIMENSIONAL ERROR IS 0.15
According to pmarc's theory (and I am all for carefully considering it) IF size tolerance (indirectly) controls form, THEN local roundness requirement is widened and default roundness is, therefore, overridden. (Am I getting it right?)
My argument is, that in absence of any rule stating how exactly compound tolerance should be distributed between its components, both requirements must be satisfied together, just like they appear on the face of the drawing: Size tolerance 0.15, roundness (cylindricity) tolerance 0.05, roundness is a refinement of size.
Case 2:
UOS MAX ROUNDNESS ERROR STILL IS 0.05 = Default requirement
MAX DIMENSIONAL ERROR IS 0.02
My argument is, that in absence of direct local roundness control, local roundness is limited by the size tolerance: Size tolerance 0.02, roundness (cylindricity) tolerance 0.02, which is still less than 0.05, so both requirements still are satisfied together. It is questionable if this condition may be called "overriding" as the global requirement is technically satisfied.
Case 3:
UOS MAX ROUNDNESS ERROR STILL IS 0.05 = Default requirement
MAX DIMENSIONAL ERROR IS 0.10
LOCAL ROUNDNESS SPECIFIED BY FCF IS 0.02
My argument is, that in presence of direct local roundness control, local roundness is limited by it: Size tolerance 0.10, roundness (cylindricity) tolerance 0.02, NEITHER SIZE TOLERANCE OR UOS RULE HAVE NO CONTROL OVER LOCAL ROUNDNESS ERROR. This is the only condition that truly may be called "overriding"
Hence my opinion is: only direct local requirement may override direct UOS requirement.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
That's something that you could have acknowledged in the previous QC Inspector thread, instead of saying that you were tired about arguing over something so "obvious."
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Can indirect control override direct one?
Sorry if I was too harsh.
You don't have a solution, but I am sure you have an opinion. If your real name being exposed prevents you from sharing your opinion with us, is it really a good thing?
So, maybe having "pen names" actually allows us to explore the problem further without looking at "ranks"?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
I suppose my opinion here would be that we shouldn't even create a situation where there is a contradiction between the general notes/title block and the callout on a particular item (kind of like 3DDave's opinion). But I'll think about it some more later today.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Can indirect control override direct one?
I would just like to add that per para. 3.5(e) in Y14.5 it is acceptable to place feature control frames in general notes.
RE: Can indirect control override direct one?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Can indirect control override direct one?
I meant 2009 version of the Y14.5.
In 1994's para. 3.5 there was nothing about FCF placement in general notes. Additionally, para. 3.3.5 said that it was prohibited to place material condition modifiers in general notes. This statement is gone in 2009.
RE: Can indirect control override direct one?
However, that is my answer only if forced to choose. The best answer is that it's a bad way to call things out, since it's confusing, as we all now presumably agree.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Can indirect control override direct one?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future