Total runout 3

[illini8181]

I have a question about total runout. My understanding is that total runout controls form, orientation and location, but not size. However, Section 9.4.2.1 of ASME Y14.5-2009 states that "Where applied to surfaces, constructed around a datum axis, total runout may be used ot control cumulative variations such as circularity, straightness, coaxiality, angularity, taper and profile of a surface." What confuses me is that this section says total runout controls profile of a surface. Doesn't profile of a surface control size?

Thanks

 

[CheckerHater]

At any rate, the paragraph in question (9.4.2.1) is talking about total runout, which is presumably applied to a cylinder, not a cone.

About Para. 9.4.2.1 "Applied to Surface Around an Axis."
It actually says: "Where applied to surfaces, constructed around a datum axis, total runout may be used ot control cumulative variations such as circularity, straightness, coaxiality, angularity, taper and profile of a surface."

Since when angularity and taper apply to cylinders?
Also, there is big picture there, Fig. 9-1 showing “surfaces constructed around the datum axis”.
There is a conical surface right in the middle of it.

So, if profile can be used to control angularity (not size) of conical surface, and total runout can be used to control angularity (not size) of conical surface, why under certain circumstances they cannot be used interchangeably?

 

[Belanger]

I agree that total runout can be applied to a cone. But I think you're still missing the big picture.

When a blanket statement is made, such as "total runout controls profile of a surface," that is saying that every time total runout is applied, you get everything that profile of a surface would control in that same situation.

But that is simply not true for total runout. You can find all the specific cases you want where it might be true (well, just one: the cone without a datum surface), but that does not justify a blanket statement implying "in all cases."

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

 

[CheckerHater]

I apologize in advance if the following appears to be harsh, but I’d like to set something straight.

I really don't think words "may be used" constitute blanket statement meaning "anyplace, anytime"

My very first post 3 days ago was: "The standard doesn’t say “runout controls all the possible cases of profile”."

My very last post said "under certain circumstances"

If somebody was making a blanket statement, it wasn't ASME Y14.5-2009, and it definitely wasn't me.

Sorry again.

 

[Belanger]

OK, I see that I was too strong in accusing the standard of making a blanket statement. You're right in that they depict total runout as controlling variations "such as..."
I suppose the phrase "such as" is not meant to be an all-inclusive list. So I concur with your point that, under certain circumstances, they are the same.
It's just that 9.4.2.1 is a strange statement because profile of a surface is not covered by total runout, other than a rather unique situation (more to come...)

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

 

[Belanger]

Well, I can't find that old thread where this issue came up (about using profile on a toleranced diameter), but I did find a graphic on my computer that I used at that time.
See the attached picture: it is my interpretation why -- when applied to a circular feature -- profile of a line/surface must be applied to a basic diameter.
First, the standard does say in paragraph 8.2 that profile is to be applied to a true (i.e., perfect) profile.

In the first picture on my graphic, no basic dim is shown because the basic dim is of course zero. But in the second, third, and fourth pictures, we should all agree that the radius needs to be basic. So why then, in the last picture, would it be OK to suddenly drop the basic dim and use a toleranced diameter? Answer: it isn't OK. And the cylinder idea that started this discussion is simply an extrusion of the last picture in my attachment.

The one exception I keep referring to is Fig. 8-17 of the standard. There the diameter can be toleranced, only because on a cone like that the profile tolerance "shell" can scoot left and right. In other words, we don't need a precise diameter to lock onto; you can move it back and forth to suit any diameter. Therefore the plus/minus tolerance on that diameter is OK.


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

 

[CheckerHater]

There were several discussions about profile applied to “flat” pieces as substitute for flatness, parallelism (in those cases not controlling size), and “real” profile controlling size as well.

If we extend the same logic to “round” pieces we will see profile acting as roundness, runout (not controlling size) and “real” profile controlling pretty much everything.

In fact profile is so versatile, it’s probably impossible to make blanket statement about it.

To me Y14-5 simply means “you think profile, but sometimes runout may be good enough” (I said “sometimes” )

 

[CheckerHater]

This is one of my old pictures, showing that profile could work both ways – with or without controlling size.

Unfortunately don’t have enough time right now to come up with similar picture for round piece.

 

[Belanger]

But your pictures are referring to profile on a single flat surface. And the basic dimension describing the shape of a flat surface is always zero. (The basic dim on your height is irrelevant to the shape, and of course profile can be used with or without a datum).

What we are supposed to be talking about is a situation where the profile wraps around the entire part, thus intersecting in some way with size.
So imagine if I added the all-around symbol to the middle picture on your graphic, CH. Would you say that the plus/minus tolerance on the height is OK?

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

 

[axym]

Hi All,

Very interesting thread, here's a quick response for now. Overall, I agree with J-P.

The statement (or intimation, anyway) that Total Runout can control variations in profile of a surface is, at best, very misleading. I wish that Y14.5 had not included this statement in the 2009 standard, and I will advocate removing it from the next revision.

Even though there may be special cases in which we can get a similar end result by using either Total Runout or Surface Profile, this does not mean that we should make this kind of statement. If we do, then by the same logic, we could also say that Flatness or Perpendicularity can control variations in profile of a surface.



Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[CheckerHater]

JP, I think there is some flaw in your logic. Both “flat” slab and the “round” piece are features of size.
The radius isn’t. So using radius as transition from square to circle is “not kosher”.
I can imagine dimensioning everything in basic, say, for profile of a wing, or some other shape consisting of several “radii”. Features of size on the other hand are pretty much controlled by, well, size. So in many cases we only need geometry control as a refinement.
So I can imagine profile being used not to its full power, but in the way that allows some other geometry control to substitute it. (Not that there is something wrong either way)

 

[Belanger]

CH -- no flaw here
This isn't about "features of size." It's about the shape of a part, and the dimensions defining that shape. So I don't care if it's a partial arc, or a full circle, or whatever shape; the rule is that a profile tolerance must be applied to a "true profile."

I think you are confusing dimensions that describe the shape of a part with size and location dimensions. (See the graphic I posted at 13:56 today.)

A couple of questions that might help here...
First, if I added the all-around symbol to the middle picture on your graphic, would you say that the plus/minus tolerance on the height is OK?

Second, if we're discussing a profile tolerance, what are the dimensions for the "true profile" for a flat slab and a round piece?



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

 

[CheckerHater]

Where do you get your ideas about "true profile" anyway?

 

[Belanger]

Directly from paragraph 8.2: "A true profile is a profile defined by basic radii, basic angular dimensions, basic coordinate dimensions, basic size dimensions, undimensioned drawings, formulas, or mathematical data, including design models." Note that this is all "perfect" stuff; i.e., basic.

And earlier in that same paragraph, it states that profile is "used to define a tolerance zone...relative to a true profile."

Put those two statements together, and you'll have the gist of my posts today. It has nothing to do with datum references or tolerancing the distance from a datum; those are separate issues.

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

 

[CheckerHater]

Is it the same paragraph that says “Where used as a refinement of a size tolerance created by toleranced dimensions, the profile tolerance must be contained within the size limits”?

Could you please explain in light of said paragraph, where is basic dimension in Fig. 8-14? Should they add “all around” symbol to it? Where is basic dimension in Fig. 8-27?

Using profile as refinement of toleranced dimensions – right there in the standard book.
Profile must always be accompanied by basic dimension – blanket statement, not really in the book.

Sorry.

 

[Belanger]

I'll try to say this gently, but you're way off track.
I am not talking about the dimensions that relate the profiled surface back to a datum or to anything else. I am talking about the actual dimensions that define the shape itself. Please notice that this has nothing to do with a refinement of size or location. Rather, it has to do with the true profile -- the shape itself.

Therefore, the basic dims that define the shape in those figures you ask about are zero! (Again, I'll refer you to the graphic I posted yesterday at 13:56 -- that might explain it better.)

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

 

[CheckerHater]

Therefore, the basic dims that define the shape in those figures you ask about are zero!

So, invisible dimensions? Two can play this game.

Look at the enclosed picture. Imagine that cylinder is actually a cone with basic angle of zero degrees (invisible). Can I use profile then? How this profile is different from total runout?

 

[Belanger]

The picture you've posted violates the Y14.5 standard, because as I've repeated ad nauseam, when profile is applied to a cylinder, the diameter must be basic. See paragraph 8.2.

If we can get past that foundational concept, then we can gladly discuss a part is truly a cone (i.e., with a designed-in angle of taper).

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

 

[CheckerHater]

I’ve read Para 8.2 ad nauseam, and it doesn’t explicitly say that basic dimensions should be used everywhere. In fact, it leaves a lot to interpretation. Do you at least accept the idea that profile can be used to control orientation? And that orientation does not require basic dimensions?

I am also disappointed that you only see zero dimensions where it suits your case.
I can see this discussion turning into bickering and will gladly leave it where it is before things turn sour. We couldn’t convince each other – better luck next time.

 

[Belanger]

Yes, profile certainly can control orientation. But that's a step ahead of what I was trying to explain. My objective was to come to an agreement on the main, essential job of profile, which is form. This is the concept where basic dimensions are required.

I didn't see the discussion going south, but I'm also willing to let it go. Peace, out...

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

 

[axym]

Hi All,

I was originally on JP's side on this, but I can see CH's reasoning as well. The problem is that the standard gives a mixed message with regards to what types of dimensions can be used in conjunction with Profile tolerances. I don't think we can say that one is right and the other is wrong - there is evidence to support both opinions.

Here are some thoughts on CH's latest figure with the Profile tolerance on the cylindrical surface with a directly toleranced diameter. Is this compliant with the standard? On the one hand, the true profile is not fully defined by basic dimensions which violates Paragraph 8.2. On the other hand, there are figures showing a Profile tolerance on a conical surface with a directly toleranced diameter. Applying this same idea to a cylinder is not a big leap. To me, the standard contradicts itself here. I would say that if you polled the Y14.5 subcommittee on whether or not CH's cylinder application is legal, the result would not be unanimous.

My personal opinion is that the true profile should always be fully defined using basic dimensions (this includes basic linear dimensions, basic angles, basic diameters and radii, etc.). This is the only path to a rigorous definition of the tolerance zone. I do not support the use of directly toleranced dimensions in conjunction with Profile tolerances, even though the standard still includes figures showing this. One reason is that these examples are non-rigorous and require certain assumptions to be made. The second reason is that these examples muddy the waters as to how a Profile tolerance zone works (resulting in many discussions like the one in this thread). In the examples involving Profile on a conical surface with a directly toleranced diameter, the form of the tolerance zone is theoretically exact but the size of the tolerance zone is not. This makes the Profile tolerance zone behave like a form tolerance or a Total Runout tolerance, but only for features that can have a directly toleranced dimension. There are no rules describing exactly how this works, only examples.

So I wish that the Y14.5 would make it clear that Profile tolerances must work in the way that J-P describes, but I acknowledge that the standard allows them to work in the way that CH describes. Y14.5 is trying to move forward with more sophisticated and rigorous Profile techniques, while not abandoning past practices involving simple geometry with directly toleranced dimensions. This is still a work in progress.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca