Can indirect control override direct one? 2

[CheckerHater]

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.


"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[PaulJackson]

I have no knowledge of the recent exchange so I'll enter the water calmly.

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

 

[TheTick]

Runout and roundness are different attributes, even though they are similar. Both are thus in force.

 

[pylfrm]

I'll put my vote in for "a) 0.05".

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

 

[powerhound]

I would say that the note applies for the reasons given by Paul. My money is on 0.05. That being said, this is a terrible note because of this thread right here. While the intent may have been clear to the author, it may not be clear to others.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[3DDave]

I think there is some prohibition on using geometric characteristics in general notes. Not sure where I read this, but I thought it is in Y14.5 somewhere.

 

[CheckerHater]

@ PJ and TheTick who refuse to see relation between Runout and Cylindricity:

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

 

[pmarc]

CH,
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.

 

[TheTick]

I'm not "refusing to see" anything. Yes, there's a correlation between runout and circularity, but there is no hard and fast, calculatable relationship. It's like the relationship between flatness and thickness. Similar, but not mutually interchangeable.

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.

 

[greenimi]

pmarc,

Is this a trap? Smell like one

 

[powerhound]

In this case, limits of size control the circularity.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[pmarc]

greenimi,
This is not a trap. By asking my question, I am just trying to answer CH's question from the title of this thread.

 

[CheckerHater]

So, TheTick, 3DDave and pmarc,

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

 

[greenimi]

0.05 on CH question (nothing else is specified for circularity to be smaller than 0.05)
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.

 

[TheTick]

My answer to your original question is "c) None of the above (please explain)".

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.

 

[greenimi]

TheTick,

Is is a hypothetical example. No deviation needed. Nothing needed to be fixed.

 

[TheTick]

Hopefully you understand the difference between runout and circularity better than you understand the meaning of "hypothetical". We were directed to imagine, which does not make the situation imaginary.

 

[greenimi]

TheTick,
I don't think so. Neither one.

 

[CheckerHater]

OK, since the experts chickened out carefully 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

 

[greenimi]

CH,

pmarc was clear on size tolerance---see his orginal posting

"Size tolerance (total) for the diameter of feature "X" is 0.02."