Runout 3

[SpaciouS]

A couple of questions on Runout,

1) It is my understanding that Runout surfaces are not defined with basic dimensions, rather, Runout is simply a surface call-out with tolerances withing the limits of size of the indicated surface. Is that correct? This is somewhat confusing since Runout is not recognized as either Form, Profile, Orientation or Location, yet I see it used with basic dimensions all the time.

2) If a part only has 1 axis, an optical lens for example, and that axis is identified as datum -A-, can you use Runout for the surfaces that defines datum -A-, and reference datum -A-?
This is another scheme I often see and do not understand.

Thanks,


Thanks,
Sean

 

[pmarc]

1) In majority of cases runout is applied to a surfaces that are associated with directly toleranced dimension for diameter. But that does not mean it cannot be applied to surfaces of revolution defined by basic diameters. See fig. 8-26 in Y14.5-2009 or similar fig. 6-17 in Y14.5M-1994.
As for runout tolerance value, it does not have to be always smaller than limits of size. Runout values greater than limits of size are absolutely legal and perfectly reasonable if location of a toleranced cylinder relative to datum axis may be greater than the one allowed by limits of size.

2) At first glance this sounds like datum self-referencing, but if you look closer it makes sense. Datum axis is derived from true geometric counterpart of external cylinder, that is from datum feature simulator being a perfect hole of certain size. However, the datum feature itself is an actual cylinder. So if you imagine that the cylinder has a form error (circularity and/or straightness), runout check will be able to detect it, because you will not be inspecting a feature which is datum and datum feature at the same time.

Side note: the other side of the story is how to physically get access to a feature that by theory shall be inaccesible due to being fully covered by datum feature simulator. But there are ways to override this problem too.

 

[powerhound]

1) You are correct. The only basic dimension applied to runout is the implied basic zero from the datum axis.
2) Yes. See Fig. 6-52 in the 1994 standard.

Runout controls all of the geometric characteristics which may be why it isn't considered any one of them.

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

 

[Belanger]

Runout can control form, orientation, and location, but not size. That's why we can't really say that runout includes profile.

For your second question, you shouldn't call out a single datum axis from a single feature and then apply a runout control to that feature referencing just that datum. To do this would boil down to circularity (for circular runout) or cylindricity (for total runout) -- it would be as useless as applying parallelism to a surface without a datum reference to gain only the flatness aspect.
But I do agree with Powerhound (notice that the graphic Powerhound mentions is OK because the 0.05 runout also references another datum, not just the self-referencing datum D).

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

http://www.gdtseminars.com

 

[pmarc]

J-P,
Are you sure that circular runout or total runout referencing to a single datum axis derived from single datum feature would boil down to circularity or cylindricity?

 

[SpaciouS]

pmarc,

Thanks for your responses. Couple questions about your answers.

Answer-1) Looking fig.8-26, it looks as though Runout is still not establishing Form, Size and/or Orientation, yet the Basic dimensions used are to govern the Profile FCF with a tolerance of 0.25 between marks A & B. Then there is a refinement in the surface tolerance, also between marks A & B , to be inspected by a Runout indicator. So I guess my real question is, can you use Basic dimensions purely for Runout FCF's, (my understanding is no).

Answer-2) Your "side note" is exactly the reason I don't understand how you can this can be done. How can you used a Runout indicator on the surface that you would be holding onto?




Thanks,
Sean

 

[Belanger]

Pmarc -- I think it would be in the case of cylindricity, because the AME you describe for runout's datum is the same as the Minimum Circumscribed Cylinder that is often used for cylindricity. (I'd have to think more about circularity because it is measured on a slice-by-slice basis, so there isn't one common envelope or MCC to start from.)

Of course, this gets into other algorithms for cylindricity such as LSC and MRS. But in general I don't think the standard ever envisions runout being used on a single feature with a single self-referencing datum. Nor would I call it an extension of principles.

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

http://www.gdtseminars.com

 

[SpaciouS]

Belanger,

I tend understand using Circularity or Cylindricity in the case mentioned (singular revolved feature).

So what I get from all of this (please bare with me):

No- you cannot use a Runout FCF on a feature with only a basic dimension and call that feature defined in terms of size? For example: Fig. 8-26 2009, if you remove the profile FCF this part would be under defined correct?

No- you cannot self-reference a datum for Runout? Or you can?

Thanks,
Sean

 

[Belanger]

The first question (Fig 8-26 without profile) -- you're correct. Runout can't control size, so the only way the basic dims make sense is that they set up a "true profile" for that profile tolerance.

The second question: Let's hear what Pmarc says but I say you cannot reference a self-datum as the only datum, because runout's main job in life is to control a feature's alignment. Thus, if you only reference yourself then the alignment is obviously perfect, and the result is that you're just controlling form.

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

http://www.gdtseminars.com

 

[SpaciouS]

Last question, I meant to add this to my previous list

I'm not sure I understand that a Runout tolerance can be greater than than the limits of size of a feature. For one reason, with Runout, rule #1 applies so to me this would imply that the Runout tolerance would have to be smaller than the size tolerance. I'm I missing something?





Thanks,
Sean

 

[powerhound]

Rule #1 applies to features of size and it only involves the form tolerance characteristics (straightness, flatness, circularity, and cylindricity). Another reason that runout needn't be a refinement of size is because runout controls coaxiality error so your feature can be well within it's size tolerance yet considerably out of coaxiality from the datum axis.

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

 

[pmarc]

J-P,
I agree that in case of total runout it would be equal to cylindricity, however for circular runout I think it is different from circularity and in certain, though very untypical, situations it may make sense. And I also agree that standard approach is to use runout for controlling feature(1)-to-feature(2) relationship, and not "runout being used on a single feature with a single self-referencing datum".

Can it be considered as an extension of principles? I am not sure. Actually, one of my New Year's resolutions is to stay away from "extension of principles" debates on this forum as most of them turn out to be double-edged sword to me.

Is it self-referencing datum? In my opinion, from theoretical point of view, it is not. It would be if positional tolerance was used instead of runout for example. In that case axis of feature's AME would be controlled/inspected relative to the very same axis, which would undoubtedly be classic self-referencing and always result in zero of actual positional error.

SpaciouS,
Aswering to your question about my "side note", follow the link below and scroll down to "Subject: Total Runout Question". Though the problem is discussed based on example from Y14.5 standard (when two separate cylinders serve as datum features), the inspection techniques described there can be transferred to a single cylinder.

http://www.geotolmeadows.com/newsletters/2012/nov2012.htm

 

[SpaciouS]

J-P

Thanks, this is a nice link to reference. Still a bit confusing to transfer this concept to a single axis feature, something I need to think on. I'm beginning to study seriously for the senior exam, and clearly I have a lot to learn still.

I find myself questioning a lot of detail drawings at my new company, designing opto-mechanics, and there is no on-sight GD&T professional (added intensive for my studies). A couple examples, almost every drawing with multiple revolved features I've seen call out Concentricity over and over, instead of Position or Runout, and most of the time these surfaces are non-functional and certainly these are parts never move in there assemblies (spin/RPM). This is odd to me and it seems like they are adding unnecessary cost to these parts. And now I'm seeing the lens drawings them selves calling for Total Runout about it's own single axis, well now I'm beginning to wonder if there is something about lens barrel and lens cell design I'm not aware of. Looking forward to learning more, hopefully I can find ways to reduce cost for this company.

Thank you everyone for you help.

Thanks,
Sean

 

[bxbzq]

Sean,

Do you work to ISO? I'm just wondering because typical ISO based drawings have a lot of Concentricity which is equal to Position in ASME to control Coaxiality.

I think it's legal to apply total Runout to single shaft part. Good practice or not? Maybe not. And in case of total Runout applied to single shaft part, the Runout tolerance should be smaller than the size tolerance because it controls only Cylindricity.

 

[pmarc]

bxbzq,
One caveat in your explanation. ISO's Concentricity is not equal to ASME's Position for coaxiality. ISO's Concentricity (which is properly called Coaxiality in case of 3D features) is equal to ISO's Position for coaxial features. But both Positions have totally different geometrical interpretations.