GD&T tolerancing of a cone using multiple segments frame 1

[2JL]

Hello everyone!

I am new to this forum though I spent nearly a year learning from valuable discussions around here.
For cones, I usually stick to a single profile tolerance but this time more control is required to better describe the functionality of the part.
Attached is a sketch of what we are thinking of doing and we are really concerned by how this would be interpreted by other people.

Basically we want the cone surface to be in maximum possible contact with his mating partner so we apply an 0.1 form tol (N°007). The axial position of the cone in respect to the datum A is not that important thus the profile tol of 1 to datum A (N°008). To finish the cone axis should be closely coaxial to the datum B and perpendicular to datum A hence the position tolerance(N°009).

Now a couple of questions:
1- Does the multiple segment frame shown in the sketch reflect the requirements described above?
2- Does the application of fig 8.18 - 2009 standard in this scenerio make sense? Should diameter DIA_5 (N°017) be based on the possible variation due to profile tol N°007 or profile tol N°008 instead?
3- is there a risk that the association of profile with position is interpreted as per fig 8.24 - 2009 standard?
4- The cyl dia is a simplification of a set of features that need to be controlled relative to the cone. Can we use the cone as secondary datum for those features?

Sorry for the long post. Any suggestions is welcome, thanks in advance.

2JL

 

[Tarator]

"The axial position of the cone in respect to the datum A is not that important thus the profile tol of 1 to datum A (N°008). "

That profile call-out does not control the axial position of the cone in respect to the datum A... their relationship (cone axis and Datum A) to each other is perpendicularity (not position)... however, with that profile call-out you control the distance of the cone from the Datum A.

 

[greenimi]

Make DIA_5 basic
Use composite profile
PLTZF profile xxx to A primary and B secondary (locate the cone)
FRTZF xxx to A primary (refine the orientation to A)

If you need a third segment could be added (with no datum)to refine the form of the cone

 

[SeasonLee]

Profile of a surface can be applied to conical part but need the basic dimension to define the conical shape, so Dia_5±e need to be a basic dimension, and the size of the cone will be toleranced by the profile control.

The conical control in this case is to control the cone concentric to datum axis B, so the primary datum would be datum feature B (which is more logic than the planar datum feature A), and I will choose datum feature B as primary datum on both position and profile DRF (datum reference frame).

I will use multiple single segment profile control to control the separate requirements, the upper segment is a profile of a surface control, it controls size, location, and orientation relative to the datum reference frame; in this case, the profile of a surface control limits the size and location of the surface of the cone. The lower segment is a profile of a line control, it controls the line elements for form and orientation relative to datum axis B, this zone floats within the 1.0 tolerance zone. The purpose of the profile of line here is to refine the form and/or orientation of line elements of the cone surface. Please ref to the attached file for details. And I will not use the position to control the cone location since profile (both profile of line and surface) already control the location of the cone.

That’s my two cents, please let me know if I am wrong.

Season

 

[greenimi]

SeasonLee,

I have a couple of questions for you and for the OP
#1: What is the advantage of using profile of a line instead of a profile of a surface?
#2: How do you know that B is primary in the assembly versus A as shown in the OP drawing? How do you know what is the physical reality of this assembly? Is B acting like primary when the parts are put together or maybe A is the one orienting the part (as originally shown)?
I do understand that you WANT (would like) to control the orientation to B, but the question is how the physical reality would look like.

I agree: Dia_5 should be basic. I also agree to not use position to control the cone location.
And by the way, I am not saying you are wrong. I am trying to learn what would be the difference between these callouts and when would you use one versus the other.

 

[2JL]

Thanks everyone for taking your valuable time to answer my questions.

Greenimi: " Make DIA_5 basic"
SeesonLee: "Profile of a surface can be applied to conical part but need the basic dimension to define the conical shape, so Dia_5±e need to be a basic dimension, and the size of the cone will be toleranced by the profile control"

You both agree that DIA_5 should be basic but it isn't what is proposed by fig 8.17 and 8.18 (2009 standard). Isn't this dimension is an indirect way to control where the cone starts or ends? (At least this is what I always thought).

Seesonlee:
#1. As you, I am not really sure about profile of line. I don't think that controlling line elements is necessary.
#2. A should stay primary (without the context B seems to make more sense).

To all: What I get from your answers is that the position tolerance is not required since the coaxiality requirement to datum B can be conveyed by a profile tolerance. Now I can't use a composite tolerance since the datum sequence in the lower segment will not match the upper segment, see the attached sketch.

2JL
Sorry for the time it took to answer. English isn't my first language.

 

[Belanger]

You both agree that DIA_5 should be basic but it isn't what is proposed by fig 8.17 and 8.18 (2009 standard). Isn't this dimension is an indirect way to control where the cone starts or ends? (At least this is what I always thought).

These two figures in the standard have caused not a little debate here in the forum and elsewhere. I will simply offer my view on things...
The definition of profile is that it be applied to a "true profile" -- that is, one where the contour itself is pre-defined by basic dimensions. So a cone should have a basic diameter.

In Figure 8-17, I would say that they're OK, however, because there is no datum at the end of the cone to stabilize where a cone-shaped profile tolerance should be. In other words, you can have a tolerance zone of the correct angle superimposed over a part, and slide the zone left or right until it finds a best fit over the actual part until it finds the diameter, which of course still needs to be within the ± range.

But in my humble opinion, Figure 8-18 is not really correct, simply because they do have a datum B which serves to locate the cone-shaped zone in a left-right manner. So the diameter should have been basic -- there is no possibility of sliding the tolerance zone left or right to overlay the actual cone.
Where are Evan or Dean when I need them? I think they've championed a similar line of thinking in the past.

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

 

[2JL]

Thanks for the explanation John-Paul.
Until this day I accepted the standard the way it is mostly because I thought it was defining the gauge plane as used in stack-up analysis.

2JL

 

[SeasonLee]

greenimi / 2JL

I’m not quite sure the application and the design intent, so it’s just based on my assumption, but from your latest gage sketch, I am still thinking you want to control the cone concentric to datum axis B, that’s why I will choose datum feature B as primary datum.

As for further consideration, profile of line will only control the line elements of the cone surface, if changing to composite profile of surface tolerance, it will control the straightness and roundness of the cone surface, probably this will more reflect your application, and how do you guys think? Please ref to the attached file.

Season

 

[greenimi]

SeasonLee,

Why A as a secondary in the FRTZF? What is the value of it? What degrees of freedom A is stopping (what degrees of freedom that haven't been stopped by A and allowed to be stopped according to the composite rules)

 

[SeasonLee]

greenimi

Here is a good example (from Genium) and it will answer your questions.

 according to the composite rules

, what's that rules?

Season

 

[greenimi]

SeasonLee,
Actually your example didn't answer my questions and in my opinion that example, from Genium, is wrong --as shown--
Why?
Because --as other people around GD and T word stated before --other threads or discussions---- reference to B (in Genium example) adds no geometrical value--

From Mark Foster
""The datum references in the FRTZF are only allowed to stop *rotational* degrees of freedom. There are no rotational degrees of freedom that B can stop that A hasn't already stopped. Therefore, the B secondary in the FRTZF adds nothing to the callout -- at least theoretically. If datum feature A were somehow unstable (a "rocker") or were referenced at MMB or LMB, then there may be some added "help" from B secondary in stopping those 2 rotational degrees of freedom, but technically we should not be "overriding" the A primary.

My comment was coming from the "Theory-to-reality" perspective. I agree with you wholeheartedly that the B secondary in the FRTZF is not allowed to override any of the degrees of freedom (rotational, since that is all that the datum references of the FRTZF are ever allowed to stop) that A primary has already stopped. However, in the real world, *IF* datum feature A were an "unstable" or "mobile" datum feature, and in reality not doing a good job of stopping those rotational degrees of freedom, then if a physical datum feature simulator were present for B, it may, in fact, do a little biasing of the part and "help" to stop those rotational degrees of freedom.

Having said all that, since, in theory, B should not be allowed to stop any rotational degrees of freedom, and therefore, in theory, B as a secondary in the FRTZF does nothing, then, in practice, one should not have called it out there in the first place.""" (Mark Foster---Applied Geometrics--)

 

[SeasonLee]

greenimi

I was shocked to know the example from Genium is wrong, it’s the first time I know that someone pointed out the mistake on Genium’s tips. I will contact with Genium to understand the right way to call out the datum reference frame.

Well, for the OP questions, I would like to know the other comments and/or suggestions.

Season

 

[greenimi]

I am curious myself what they have to say about their own example and also what others GD and T knowledgeable gentlemen’s on this form have to say about it.
Pmarc, where are you when I need your help?
I don’t know if I can “survive” without your help, please......

 

[3DDave]

Datum B serves to locate and orient the gauge for the diameter measurement. Were it not in place the offset would be perpendicular to the origin surface. No doubt the thinking was that B had to be mentioned somewhere, even though it serves an entirely different function in this DRF than it would if it was describing a different feature tolerance.

This is the sort of ambiguity that Y14.5 cautions against. All the cone dimensions that control the taper and location should be basic.

 

[Belanger]

All the cone dimensions that control the taper and location should be basic.

And size. (Explained above.)

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

 

[3DDave]

I've thought that cones and tapers have no size; the reason being that any value one might place on a section dimension can always be met at some place along the axis. Typically, where it is important to know a 'size,' one is making an arbitrary change to that location. At the intersection all tapers are zero section size and at infinity all tapers are infinite section dimension.

I'd prefer if the dimensions along an axis were taken from the intersection point, which has no size and will always be the place that exactly aligns with a mating taper.

In any case this means that only the taper angle dimensions the taper. Where it starts and ends are dimensions of those features.

 

[Belanger]

I've thought that cones and tapers have no size; the reason being that any value one might place on a section dimension can always be met at some place along the axis.

But notice in this case there is a datum B which locates the tolerance zone at a prescribed distance from the left end. Thus our profile toleranced is anchored (thus the diameter shouldn't have a ± tolerance).

Without datum B, I agree that the size could be toleranced because we wouldn't have anything to anchor the profile tolerance in the left/right direction.

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

 

[greenimi]

Son let's clarify a little bit: only PLTZF locates and B as secondary is needed.
FRTZF never locates (only orients) and that's why B is not needed (does not add any geometrical value if it is added on FRTZF)
Just my opinion.

 

[3DDave]

The method given is not a functional description. If B was located from the sharp intersection, the size dimension would not be required; it would make no sense.