Must profile be applied to a basic profile?
Must profile be applied to a basic profile?
(OP)
Several things have popped up in various threads that always seem to leave this question lingering: When a profile tolerance is applied, is it required for the dimensions defining the shape to be basic?
We all agree that the dimensions defining the location of the feature do not have to be basic (often they are). So please realize that I'm talking about the shape -- such as the radius of a curve: I would say that the radius must be basic if you're going to apply a profile tolerance to such a curve.
See the attached picture for the specific question to be debated. Would you say the two drawings mean exactly the same thing? Or would you say the second drawing does not comply with Y14.5?
We all agree that the dimensions defining the location of the feature do not have to be basic (often they are). So please realize that I'm talking about the shape -- such as the radius of a curve: I would say that the radius must be basic if you're going to apply a profile tolerance to such a curve.
See the attached picture for the specific question to be debated. Would you say the two drawings mean exactly the same thing? Or would you say the second drawing does not comply with Y14.5?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems





RE: Must profile be applied to a basic profile?
I say both comply.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
Whenever a profile is used, it is associated with a true profile (a surface defined with basic dimensions). (Here is the part that seem somewhat contradictory) The true profile may be located with basic or toleranced dimensions relative to the datums referenced in the profile control.
He states a surface defined by basic dims but then says toleranced dims are OK. ???
This is followed by this image.
As you can see there are both basic and toleranced dimensions.
So, as to your original survey:
1. Is OK. The part must not be smaller than 14.5 nor larger than 15.5 and the smallest actual diameter must be within the cylindricity callout of the largest actual diameter of the part.
2. I think would be OK if the diameter was not given as a max/min. With the max/min you do not know what the actual target is. Is the perfect part 15 ±0.5 or is the perfect part 15.5 with a +0/-1 tolerance. or some other non-symmetric tolerancing scheme
RE: Must profile be applied to a basic profile?
The important question is whether or not I can interpret your drawing.
Your Ø15.5/14.5 dimension allows the bar to be curved, or flowerpot shaped, as long as nothing exceeds the tolerances. In that context, your cylindricity forces the part to be straight and round, but it does not control the size. Your diameter tolerance is required.
On your second diagram, the profile tolerance controls the size, overruling your tolerance. Given your limit tolerancing, I claim that your nominal size is ambiguous. The dimension must be basic. I put profile tolerances on large, round clearance holes all the time. The profile controls the exact (but usually inaccurate) composite outline that I am interested in.
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JHG
RE: Must profile be applied to a basic profile?
I did find the statement regarding the necessity of "basic" dimensions.
Short answer: not required
Long answer: paragraph 8.2 of ASME Y14.5-2009, next to last sentence; Where used as a refinement of a size tolerance created by toleranced dimensions, the profile must be contained within the size limits
Based on that wording I change my response regarding drawing #2.
This is OK also. With the condition that regardless of the profile tolerance the largest this part could be is 15.5, smallest is 14.5. However the profile tolerance will always be inside the 15.5/14.5 size limit.
As in Krulikowski book, if any portion of the 55.4/54.8 surface is only 54.8 from datum B, then he furthest any part of this surface can be from B is 55.0 and the allowance to go to 55.4 goes out the window. And like-wish if part of the surface is 55.4 form B the closest any other segment of that surface can be is 55.3 and same issue with the size limit, 54.8 no longer valid.
RE: Must profile be applied to a basic profile?
In a narrow, technical sense, the dimension attached to the profile tolerance does not absolutely have to be basic. I cannot see a situation where it would be anything else. Profile tolerances control just about everything. If I have a composite FCF with a stack of increasingly accurate tolerances, the profile will be on the bottom. The controls on top will be straightness, flatness, perpendicularity, parallelism or something like that, refining the relatively sloppy profile.
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JHG
RE: Must profile be applied to a basic profile?
RE: Must profile be applied to a basic profile?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Must profile be applied to a basic profile?
14.5-15.5 has no nominal... we don't know where the true profile lies... it's floating, therefore you can refine it with a profile call-out.
15±0.5 has a nominal, and a true profile which is a dia15 cylinder. Therefore profile call-out would be wrong... Either, replace it with a cylindericity call-out, or change 15±0.5 to 15 BASIC.
RE: Must profile be applied to a basic profile?
Let's take a look at the definition:
The part marked in red clearly states that Profile is intended to control FORM with or without SIZE.
It's right there: "tolerance zone to control form, or combinations of size, form..." etc.
The part marked in green clearly states that size may be controller by directly toleranced dimension.
It's right there:"size tolerance created by toleranced dimensions"
What is obviously there, but many choose to ignore it, that directly toleranced size trumps Profile.
It's actually right there: "used as a refinement of size tolerance" - in presence of directly toleranced size profile is relegated to secondary, "refinement" function.
So, if you read it together you clearly see this:
1. Size may be controlled by profile or direct tolerancing
2. When size is controlled by directly toleranced dimension, profile controls form (or orientation, or whatever)
And yes, 15±0.5 and 14.5-15.5 mean exactly the same
RE: Must profile be applied to a basic profile?
I think you and I are on the same page. And I even thing I agree that, in THIS instance/subject matter 15±0.5 & 14.5/15.5 mean the same, but not ALWAYS.
With regard to the use of the profile callout on the OP's #2, if the diamter was a basic dimension on his drawing then the tolerance zone would be half insdie the true profile and half outside. Were as with the use of a toleranced dimension (which falls under what I said earlier and your green highlighted section) the the profile zone will always be smaller than the largest tolerance dimension allowance and larger than the smallest tolerance allowance.
OP,
I still have trouble with some of the finer details of ASME Y14.5, and you obviously based on your signature are somewhat of an expert on the subject, so, what is your take.
RE: Must profile be applied to a basic profile?
CH, you say that the original two pictures have identical meaning. And I hear what you're saying about par. 8.2. Then, based on your explanation, the picture I've attached would be perfectly fine?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Must profile be applied to a basic profile?
Radius in not size. Is that enough?
RE: Must profile be applied to a basic profile?
Belanger, based on what I think we have agreed on regarding par. 8.2 (tolerance dimesnion are acceptable), I think this drawing is OK. Other than the 42 might as well be a basic dimension because the ±0.5 has no value. Due to the profile tolerance refinement of the feature, wouldn't the part be forced to fit into a 42±0.2 tolerance?
RE: Must profile be applied to a basic profile?
May I ask question back?
Which example in the enclosed picture is, in your opinion, wrong?
RE: Must profile be applied to a basic profile?
I'll explain.
I was arguing that size could be refined by profile, and in that sense there is nothing wrong with applying profile to directly toleranced feature. (Which doesn't mean that we should always do that)
There are also other possibilities where profile may be used together with non-basic dimensions (see the picture and note that it still about size mostly).
Belanger gives example of some taken out of context situation, which doesn't make much sense by itself. (By the way the definition of radius in standard is not perfect either).
So, I explain that my post (that has word "size" repeated 9 times) does not automatically applies to all possible combinations of dimensional/geometrical controls.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
ORIENTATION: same basic scenario as FORM, the profile still further refine the positon tolerance of the line 20 units from datum A to ±0.05
LOCATION: probably the best dimension scheme of the four, with the 20 being “basic”, there is no question about the dimension tolerance with respect to the profile tolerance
FORM & SIZE: same as the others, other than this allows the 20 to go to 20.2 max and a 19.8 min, whereas the others restrict the max 20 dimension (regardless of a round or flat feature) to 20.1
???
RE: Must profile be applied to a basic profile?
don't you have that backwords?
RE: Must profile be applied to a basic profile?
It doesn't have as much power as if it was controlling basic dimensioned feature.
That's what I meant.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
In your diagram, anything conforming to the 0.4 profile tolerance, easily conforms to the R42±0.5. The radius tolerance is redundant. The dimension might as well be basic, indicating that the feature is controlled by an FCF.
In effect, the R42±0.5 is not wrong. It just does not provide any information.
Let's come at this from the opposite direction. I have a piece upon which I apply a profile tolerance of 0.8mm all around the outline. On one feature of the outline, I apply a dimension with a tolerance of ±0.1mm. My assumption here is that all the applied tolerances must be met by the part. The ±0.1mm tolerance is tighter than the profile tolerance. Parts not meeting this will be rejected even though otherwise, they meet the profile tolerance. Note how the profile tolerance acts as a position tolerances on the accurate width.
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JHG
RE: Must profile be applied to a basic profile?
CH -- this part is directed at you also... Let's go back to drawoh's first statement... "Anything conforming to the 0.4 profile tolerance, easily conforms to the R42±0.5." But since we're dealing with curvature, what exact curve must that profile zone be built around? Drawoh would say 42.0. I think CH would say any radius between 41.5 and 42.5. Thoughts?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Must profile be applied to a basic profile?
I TOTALLY disagree. CH you and I both posted the parargraph directly from the spec.
Where used as a refinement of a size tolerance created by toleranced dimensions, the profile must be contained within the size limits
My interpretation of this is that it is exactly what it says it is "a refinement of a size tolerance". Meaning that if my dimensional tolerance allows the part to be ±0.5 (using OP's original example)
1) the part is never allowed to biggger or smaller than the an assumed nominal of 15 by 0.5
2) however the profile call out requires the largest and smallest diameter on the part to be within 0.2 of each other
RE: Must profile be applied to a basic profile?
I already said it once and I will say it again - the way it's shown on your picture it simply makes no sense.
RE: Must profile be applied to a basic profile?
This is how "refinement" works.
This is why both +/-0.1 and +/-0.05 are required in example of form.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
CH, just an FYI, it is hard to tell who you are responding to, maybe you could add a name or initial of the poster you are referring to at the beginning of your statementsBelanger,
I think it depends on how the toleranced dimension is written.
42±0.5:
Is pretty straight forward that the target is for the radius to be 42 but is allowed to vary by ±0.5; however the profile callout makes the ±0.5 useless because (by definition) the profile is a refinement of the tolerance dimension. Therefore the ±0.5 might as well not be there at all and this could be a basic dimension with the profile allowing it to be as small as 41.8 or as big as 42.2 and meet the drawing requirements. Or one could just drop the profile call out and make the radius dimension 42±0.2 and have the same thing.
Now if the radius dimension was stated as 41.5-42.5:
This scenario if different and it would seem that the part could be as small as 41.5 or as large as 52.5, but the profile tolerance will require that whatever the largest and smallest diameters are (within the ±0.5) they must be within 0.4 of each other.
???
RE: Must profile be applied to a basic profile?
I was interpreting the par. 8.2 toleranced dimension referecne as still applying to the "true profile".
Your attachement indicates that you think this part of par. 8.2 applies the the "real (as manufactured)" part surface.
???, I'm not really sure what is correct at this point.
RE: Must profile be applied to a basic profile?
Wow. How you apply toleranced dimension to "true profile"?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
I have nothing else to add, though, I've just been reading along and appreciating the education, so far. Thank you
RE: Must profile be applied to a basic profile?
RE: Must profile be applied to a basic profile?
RE: Must profile be applied to a basic profile?
Profile tolerances control everything. As such, if there is a profile tolerance on something and one or more other controls, the other controls refine the profile tolerance. I don't see how you can apply a profile tolerance as a refinement of something. I understand the concept. I just don't think it applies to profile.
If you apply a profile tolerance to a radius, you must have a nominal radius. Given a dimension of R42±0.5, I would guess 42 as the nominal radius. A case can be made for R42.5!
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JHG
RE: Must profile be applied to a basic profile?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Must profile be applied to a basic profile?
Where exactly does it say that toleranced dimension implies "nominal" or "target" value?
As far As I can remember, all different ways to represent the tolerance (limits / bilateral / unilateral) have exactly the same meaning.
Could somebody quote the actual standard?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
If I'm hearing you, the first picture (arc) is not allowed per Y14.5, but the second picture (circle) is allowed.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Must profile be applied to a basic profile?
I'd say it would be interpreted the same way as cylindricity, but it won't provide any special benefits, which may be the reason you don't see it very often
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
Reading 14.5-2009, Chapter 2 consistently refers to the stated dimension as the "nominal" value when using bilateral or unilateral tolerancing. The section on 'Limits' dimensioning has no mention of the word nominal.
RE: Must profile be applied to a basic profile?
I am looking at Figure 8.27 here, and I am finding it weird, although it makes sense. The 80±0.2 is a measurement with calipers across the faces. The second part of the figure does not account for the profile tolerance. The profile tolerance controls the top face with respect to datum A, datum A being whichever three points of the surface contact your flat granite block. That bottom face could be way out of flat.
Why would I do this? If I want some face to be profiled to 0.07mm with respect to the opposite face, I am going to pay attention to the opposite face. It is going to be very flat, or there will be three datum targets, or there will be some other unambiguous geometry to define the datum.
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JHG
RE: Must profile be applied to a basic profile?
Yes, and ANSI B4.2 uses term "basic".
I guess I was unclear. Where does it say that "nominal" represents the "target" and limits dimension somehow have special meaning different from "-lateral" ones?
What disproves (or proves) that shown ways of dimensioning are not equal?
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Must profile be applied to a basic profile?
Wow, this has become quite a thread. The discussion is similar to previous discussions over the years in other forums, and in the standards committees ;^/. Sigh. I've also had to think about how plus/minus tolerances affect profile tolerances for committee work fairly recently, so this is unfortunately familiar ground. When plus/minus tolerances are involved, the discussion inevitably grinds down into opinion-based interpretation because plus/minus tolerances are ambiguous and don't have rules.
With regards to the original question, I would say that the two drawings comply with Y14.5 and would apply the same tolerance requirements. I wish that it were otherwise and I don't think that combining +/- with profile is a good practice, but Y14.5 does currently allow it. CH's references are correct, and there are figures showing examples.
There is a very mixed message in the standard. Profile is mainly described in terms of true profiles being defined using basic dimensions, and I would say that this is definitely the best practice. Nevertheless, there are figures showing profile tolerances combined with plus/minus size tolerances. In Y14.5-2009 see the following:
-Fig. 8-17 where profile controls "conicity" but not size. This can be extended to apply to JP's initial cylindricity/profile example, since a cylinder can be thought of as a cone with an included angle of zero.
-Fig. 8-18 where profile controls form, orientation, and location (but not size). I would say that the appropriate characteristic for this type of control would have been total runout, not profile. But Y14.5-2009 does not allow (or at least does not show examples of) total runout on conical features. Part of the reason for this is lack of agreement on how plus/minus tolerances would be interpreted (such as the 45 +/- 2 degree cone angle in Fig. 9-2 for circular runout). Some argued that the nominal angle represents the "true geometric shape" and would be different if the tolerance was unilateral (43 +4 -0), others argued that no true geometric shape is defined, others argued that the cone angle would have to be basic. This is a major example of how the ambiguities of old-school plus/minus tolerancing clash with geometric tolerancing.
-Fig. 8-27 where profile controls form and orientation, but not location. In this case the location is height, and is controlled by a directly toleranced size dimension. I've ranted about this example before, on this forum, probably more than once. The only "explanation" given is that "In this application, the datum references only orient the profile of a line tolerance". We are left to wonder exactly how this happens.
These figures are problematic for several reasons. One reason is that they are example-based and case-specific. Without a general description of what a directly toleranced dimension does to a profile tolerance zone, we are on our own with examples that are not shown. Another reason is that these figures undermine Y14.5's own directive of using geometric tolerances to locate features. The plus/minus tolerances introduce non-rigorous and ambiguous aspects such as the orientation relationship between the size dimension and the geometric tolerance zone and DRF (if present). Another problem I have with 8-17 and 8-18 is that the size dimension is on a surface in which the points are not fully opposed - this would introduce additional errors and uncertainty (especially if the included angle was significantly larger than the 15 degrees in the figure).
Regarding whether or not profile can be applied with a directly toleranced radius, who knows? There is no figure showing this, so we really can't say for sure.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: Must profile be applied to a basic profile?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Must profile be applied to a basic profile?
First, a conical surface in isolation has a single parameter: angle. There can be no notion of size for a cone without involving other features / surfaces / datums / etc. What might be thought of as "size" is really just a matter of what portion of the surface you're looking at.
In Fig 8-17, the true profile of the cone is fully defined by the basic angle. The profile tolerance has no datum references, so "conicity" is all it can control. The way the I see it, the diameter tolerance just controls where the flat face ends up relative to the cone. It has nothing to do with the profile tolerance. Even if it were basic, the meaning of the profile tolerance would be unchanged.
I don't think Fig 8-17 can be directly extended to the original cylindricity/profile example though. When the basic angle goes to zero and it turns into a cylinder, a second parameter is required: diameter. This was not provided as a basic dimension, so I don't think the definition of a true profile in paragraph 8.2 was met. I'm still unclear on whether a profile tolerance can be applied without a true profile though.
In Fig. 8-18, the cone is not fully related to datum B by basic dimensions. Orientation is already controlled by datum A, so I don't think datum B actually changes anything for the profile tolerance (if you accept the idea in Fig 8-27). The "Means this" explanation implies this as well: when describing the profile tolerance boundaries, datum B is not mentioned. Again, I think the diameter tolerance (this time at the gage line) just controls the relationship between the cone and flat surface, not really "size" of the cone.
Or am I off-base here?
- pylfrm
RE: Must profile be applied to a basic profile?
I guess I don't really have an issue with Fig. 8-17 because there are no datums. The profile tolerance can slide (or shift) left and right until it superimposes properly along any diameter. It is controlling form, but doesn't have any way to control diameter because there is no datum in the longitudinal direction. (With my original graphic of a cylinder, there was no taper to speak of so the diameter to me should have been basic.)
But Fig. 8-18 sticks in my craw because of datum B, which locks the profile tolerance at a precise left/right location. So my thought is that the diameter shouldn't be basic. But based on the discussions here, I suppose the consensus is that it's technically legal. Shrug.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Must profile be applied to a basic profile?
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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.
RE: Must profile be applied to a basic profile?
I tend to place a sloppy profile tolerance all around my parts. Then, I apply the other controls, particularly parallelism and perpendicularity on the features that require them. On its own, profile does control everything. Generally, you don't want to make everything ultra-accurate.
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JHG