Surface location 2

[gabimo]

Relatively new working with GD&T and on this forum.
ASME Y14.5-2009

Does the total runout (as a lonely requirement) shown control the surface location?
Again, the surface LOCATION, not the axis location (coaxiality).

Or the surface location is controlled by the combination between the total runout and size? (not the total runout by itself as a stand-alone callout/ requirement) ?

As we know, runout does not separate form and location deviations, so the amount each of these deviations contribute to the runout deviation will not be known. The verification of a runout tolerance reports the cumulative effects of form and axis offset. But the question is about the surface location.

Y14.5-2009 states:
9.4.2.1 Applied to Surfaces Around an Axis. Where
applied to surfaces, constructed around a datum axis,
total runout may be used to control cumulative variations
such as circularity, straightness, coaxiality, angularity,
taper, and profile of a surface.

 

[3DDave]

I would separate descriptions of the sort of controls a datum reference provides from the ones a geometric characteristic does. Every characteristic that is linked to an axis as primary is limited in the same 4 degrees of freedom.

 

[gabimo]

Evan,
May I ask you, if you don't mind, why the runout is not explained, in the standard, in tolerance zone terms instead of FIM, in the same way you stated above?

What would be the advantage of the current explanation " means this" ? Maybe simplicity? Legacy?

Thank you Evan for your entire input on this discussion.

 

[mkcski]

gabimot:

FYI The 2015 DRAFT of the next release of Y14.5 has extensive revisions to Runout and eliminated words referring to the type of measuring equipment to be used - like dial indicators and FIM. I have a copy of the DRAFT but it is too much to attach to a post.

Certified Sr. GD&T Professional

 

[greenimi]

Per 2009 : Tolerances of Location.

Runout is NOT included amoung the callouts that control LOCATION.

This Section establishes the principles of tolerances of
location. Included are position, concentricity, and symmetry
used to control the following relationships:
(a) center distance between features of size such as
holes, slots, bosses, and tabs
(b) location of features of size [such as in subpara. (a)
above] as a group, from datum features, such as plane
and cylindrical surfaces
(c) coaxiality of features of size
(d) concentricity or symmetry of features of size—
center distances of correspondingly located feature elements
equally disposed about a datum axis or plane

I mean "directly" control location ( and a new can of worms is opened: What means: directly, indirectly, default, specified otherwise, unless otherwise specified, refinement.........)

 

[mkcski]

Greenimi:

There is a (implied) relationship between runout and location control in Section 7.6 coaxial Feature Controls - at paragraph 7.6.3 (page 153 in 2009).

Certified Sr. GD&T Professional

 

[greenimi]

Well I don't know if the following paragraphs will bring any clarification:

7.6.3 Runout Tolerance Control
For information on controlling surfaces of revolution,
such as cylinders and cones, relative to a datum axis,
with a runout tolerance, see para. 9.2.

and

9.2 RUNOUT
Runout is a tolerance used to control the functional
relationship of one or more features to a datum axis
established from a datum feature specified at RMB.
NOTE: The figures in this Section use measurement techniques to
explain the tolerance zones. It is neither the intent nor within the
scope of this Standard to define measurement methods.


7.6 COAXIAL FEATURE CONTROLS
Coaxiality is that condition where the axes of the unrelated
actual mating envelope, axis of the unrelated minimum
material envelope, or median points, as applicable
of one or more surfaces of revolution, are coincident
with a datum axis or another feature axis. The amount of
permissible variation from coaxiality may be expressed
by a variety of means, including a positional tolerance,
a runout tolerance, a concentricity tolerance, or a profile
of a surface tolerance.

At least not to my level of understanding.......For what I understand, so far, the runout is MORE connected/ controlling the axis location/variation, but not the surface location. Am I correct?

 

[axym]

gabimot,

As mkcski mentioned, the Y14.5 public review draft has tolerance zone descriptions instead of the FIM descriptions.

Why didn't this happen before? You're right that simplicity and legacy were major factors. We studied this a few years ago and came up with some zone-based descriptions to present to Y14.5, and a the time they decided to stick with the indicator descriptions. It turns out that the runout tolerances are very easy to describe and understand in terms of the indicator inspection method, and very difficult to describe and understand in terms of tolerance zones. More so than any other geometric tolerance type. The zones can be odd shapes that are difficult to describe in words, particular for circular runout. Planar slices, cylindrical slices, conical slices, etc. Total runout is easier - the zones are like shells that are the same shape as the nominal feature. The main difficulty is that the FIM concept enables a "progression" transformation that manifests itself differently depending on the feature geometry - for cylinders it's a size-like transformation, for planes it's a translation-like transformation, and for other surfaces of revolution it's a combination of the two. It's bizarre, and non-intuitive for many people.

greenimi,

Try not to read too much into the rough classifications that the GD&T standards use. As you know, most tolerance types control some combination of form, size, orientation, and location. Position is in the Location category, and does control location, but usually controls orientation as well. Orientation tolerances can control form as well as orientation. A profile of a surface tolerance zone can be completely constrained in all aspects relative to a datum reference frame. If this isn't location control, I don't know what is. But profile of a surface is not in the Location category.

So just because runout tolerances are not included in the Tolerances of Location category, this doesn't mean that they don't control location. As you and mkcski pointed out, runout tolerances are mentioned as a coaxial feature control and control the "centering" of the feature. This is because runout tolerance zones are radially symmetric to the datum axis. So they control the "coaxial" aspect of location. But not the "surface location" aspect, as you describe. Again, the classification into form/size/orientation/location becomes somewhat ambiguous when applied to runout tolerances.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[mkcski]

greenimi:

I will not attempt to repeat the extensive postings already made to answer your question: " Am I correct?". But here is my two cents: the issue wiht this thread appears to be the meaning the words - location vs position. The meanings are interchangeable for the average Joe. But in the GDT world, position is one of the location controls. Runout is a composite control that limits form AND location error simultaneously (I'm intentionally not using position here). My recommendation: study position (of the center of a feature) and then get a good grasp of form (shape of the feature's surface). Then see how the two interact with runout, you will then get a clearer picture of why this OP has been going on for days.

When the light comes on, there are other things that will be "obvious". Like: runout applied to surfaces normal to the datum axis control form and orientation (not location). And, if the runout tolerance is less than the feature's size (diameter) tolerance - the size tolerance limits the form error (Rule #1) and the runout tolerance is all location.

Certified Sr. GD&T Professional

 

[powerhound]

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[axym]

mkcski,

I agree that the main issue with this thread is the interpretation of the words. We have seen that "location" can mean different things to different people, and "position" definitely means something different in Y14.5 than in common technical English. They say that the runout tolerances are composite control - but even there, the word "composite" is used in a different way than it is in other sections of Y14.5 (the composite feature control frame, which is something totally different). Also, there may have been a typo in your last post - if the runout tolerance is less than the feature's size tolerance, then the runout tolerance would limit the form error.

John,

That's funny. But you said something that turned out to be incorrect, in good faith, it's not misinformation. If you feel that the discussion changed your understanding, it's gracious of you to say so.

These discussions are sometimes both disheartening and encouraging. On the one hand, if a bunch of GD&T professionals are arguing over whether or not runout controls location, in 2017, then we haven't done a very good job explaining it in the standards. On the other hand, there is a big opportunity to explain it better. I find that at a certain point, the words fail. I tend to revert to mathematical/geometric descriptions, that are much less open to interpretation and can be objectively tested.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[Belanger]

I've read all of this and the conclusion seems pretty straightforward: Runout controls location in the sense of axis location, but not surface location because the size of the feature will have a tolerance that compounds with runout into controlling the surface.
I'm not saying the arrival at that conclusion was straightforward! Kudos to you guys for fleshing out all the details.

By that same token, we should say that position doesn't control location ... of the surface. But doesn't that sound strange? We all know that position is a "location" control.
So as Evan has point out, it comes down to terminology, and I guess we need to be careful and distinguish between axis location and surface location. This distinction is true for most of the GD&T world.

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

 

[mkcski]

axym:

Yeah, words - written and verbal - are a big "problem" in the world in general, and not just in GDT. Did ya ever consider that a dictionary uses words to define other words. Geez, talk about a spiral of confusion. Then consider the translation errors from one language to another. Then add the vocal and body language that goes with in-person communication. How does the world run at all and come to agreement as to what is being communicated? By careful listening and discussion, which is what we are doing in this forum. Sorry for getting a little philosophical, but I could't help myself.

Certified Sr. GD&T Professional

 

[powerhound]

I've been reminded that I needed to get back to this thread and acknowledge Evan. Yes, this has changed my understanding of runout. Breaking it out like this makes it so obvious but it's just not something I had given much thought to. It just makes me glad I frequent these forums and don't just live in my own little echo chamber where I totally agree with everything I say.

Thanks again, Evan.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech