Total Runout putting limits on dimensional tolerance

[roberto1brazil]

Hi, I have checked some previous questions about this matter in this forum but anyway I would like to be sure.
Please, could someone confirm my following doubt and interpretation?
Is it possible to have a dimensional tolerance (diameter ) of 0,005 mm and a total runout of 0,02 mm for the same feature in relation to the data displayed? I have received a drawing (see just a sketch attached as reference) from our main site, but for me it makes no sense.
Thanks and regards.
Roberto

 

[ewh]

Yes... the feature may meet the size tolerance but be skewed or offset from the centerline, thus the runout tolerance.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[dgallup]

Absolutely. Runout does not control size. It controls form and location. In this case it would have little influence on form because the size tolerance is much smaller but it will control location.

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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.

 

[CheckerHater]

No, total runout does not put limits on dimensional tolerance.

You maybe mistaking it with some other control(s).

I recommend looking on the following newsletter, that makes distinction very clear:

http://www.mechsigma.com/newsletters/2003_10_Newsletter.pdf

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

 

[3DDave]

The datum reference frame is overconstrained. There is no need to refer to as [A] already constrains orientation.

 

[roberto1brazil]

Thanks all of you for the explanations and examples. Changing the symbol from total runout for the one of concentricity, I can imagine that we can have a closed diameter size tolerance with a center only offset 0,02 mm from the data reference. Now it makes sense for me the total runout controlling the position. In fact I was accustomed to find only size tolerances greater than total runout tolerance, according to the example from ChekerHater.
Roberto

 

[ak762]

The datum reference frame is overconstrained. There is no need to refer to as [A] already constrains orientation.

Will it make sense if the datums change a place in the frame to put as primary and [A] as secondary?
I've seen the similar sample Fig9-7 in ASME Y14.5-2009

 

[dgallup]

That would make no sense. What 3DDave is saying is there is no need for B at all for a runout or concentricity specification.

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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.

 

[3DDave]

Datum A constrains 2 rotation and 2 location degrees of freedom. In the initial FCF this is identical to the variability in the feature, leaving no unconstrained rotation or orientation movement.

Datum B constrains 2 rotation and 1 location degree of freedom, but in the initial FCF the one location isn't relevant to controlling the feature.

This means if A is primary there is no need for B, but if B is primary there are still 2 location degrees of freedom that need a constraint. Those can be supplied by using [B|A] which ignores the rotation degrees of freedom from A in favor of those from B, and adds the location degrees of freedom from A to give each of the degrees of freedom in the feature a way to be measured.

[B|A| is typically used if there is a bolted flange that will force the face to be the primary alignment.

 

[patdh1028]

Are "overconstrained" DRFs a problem for orientation? I do it pretty regularly myself - I've seen the overconstraint interpreted as "adding stability" to the DRF/DFS; like instead of theoretically allowing the part to float along the axial translation allowed by only having datum A in the callout, you can add B to the FCF just to "ground" the DRF even though it doesn't modify the tolerance requirements at all. I do this to have homogeneous DRF's - if I'm controlling locations and profiles from a given DRF and I want to control orientation, I use that same DRF in the FCF rather than truncating one or two unnecessary datums. I think of it like saying "when you measure this, leave the part wherever it was set up to measure the other features." Can't hurt, right? Or am I missing something?

 

[JNieman]

You shouldn't add anything that isn't necessary to the function of the part. Often times it can come back to bite you when perfectly functional parts might be rejected because they didn't pass a FCF that tied it to a Datum that didn't impact fit, form, or function.

_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[3DDave]

The simultaneous interpretation only applies to position and profile. There's no support for applying it to other controls.

 

[patdh1028]

I definitely see where you are coming from, but I don't see how a fully-constrained DRF could possibly be more prone to error in measurement than a floating DRF. If I have a fully constrained DRF and don't "need" it for an orientation control, I wouldn't think that it could possibly hurt in the way you're saying (assuming that the orientation requirement itself is appropriate to the form/fit/function). On the flip side, using a partially-unconstrained DRF introduces opportunity for practical measurement error between the shop and the company. It's orientation we're talking about so with theoretically perfect measurement capability, whether or not the DRF is fully constrained or not shouldn't matter. But if I put such an FCF on the drawing I would (and do) expect that the difference between the measurement done at the machine shop and the measurement done at my company will be less variable than a floating-DRF FCF. To put another way, I think we may agree that to get the best-quality measurement you want to change the measurement set-up as infrequently as possible, right? And if that's true I only see benefit from establishing a fully-constrained DRF and then using it for all required controls, orientation included, even though for some controls such constraint will not be mandatory per the standard. It's not adding any requirements to the tolerance, but it is adding requirements to the measurement process.

 

[3DDave]

Users are free to add their own interpretations, but not everyone will follow or make the same sense out of them. In this case the OP was originally asking for the part to be positioned against a stop in a way that doesn't influence determining where the axis of rotation is to evaluate runout. It's like using "+ 0" in addition problems. There's no effect and other users won't understand why the requirement is there. It also won't show up in any good tolerance analysis.

 

[CheckerHater]

To be fair, I've seen worse crime committed in the world of GD&T

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

 

[powerhound]

I agree with Dave. Having the end of this part specified as a secondary datum does nothing at all other than to confuse someone with only a cursory knowledge of GD&T. To a knowledgable user, they will either ignore it, or make a call to see what the designer meant.

Dave, I think the simultaneous requirements rule has changed since 1994. It used to apply to features located using basic dimensions (thus position and profile). Now the standard says it applies to position AND only features of size are referred to. If you know of somewhere else in the standard that profile is supported please let me know cause I can't find it. I don't think I like this new definition if it proves to be true.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech



SSG, U.S. Army
Taji, Iraq OIF II

 

[CheckerHater]

If you know of somewhere else in the standard that profile is supported please let me know cause I can't find it.

Here

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

 

[powerhound]

This doesn't support simultaneous requirements as it applies (or not) to profile. The OD of this part is constrained to the DRF via the Profile FCF.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech



SSG, U.S. Army
Taji, Iraq OIF II

 

[powerhound]

Never mind. I followed the references in the bottom right corner of the figure and found what I needed.

Thanks CH.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech



SSG, U.S. Army
Taji, Iraq OIF II