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

 

[Belanger]

Not sure I understand, Dave. (Maybe we're talking about different things.)
If you don't mind... let's focus on Figure 8-18 of the standard. It's kind of the same thing, but not composite. I've always had an issue with that one so that's why I'm asking you. Please read my post above from 16:26 on Feb. 23 and let me know your feedback.

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

 

[3DDave]

I'm saying that giving a taper an angle, a diameter, and an offset from a location is double dimensioning and so 8-18 is defective because of it. The only dimensions required are the angle and the distance from the surface used as B to the sharp. Any other scheme is adding unnecessary dimensions.

 

[greenimi]

3DDave and J-P,

I have some questions for you, if you don’t mind:
1. In my opinion, the picture attached by SeasonLee from Genium is a better representation, or more robust definition of the cone--Profile Tolerancing of a Conical Feature, Datum Related--, than fig 8-18 (shown in the standard Y14.5-2009). Do you agree? If not, why?

2. In the same token (Genium picture), do you agree, that datum feature B, used as SECONDARY in FRTZF (AGAIN, secondary in FRTZF) is useless (has NO geometrical value)

Thank you

 

[Belanger]

Greenimi,

First, I'll keep beating my same drum that both pictures are flawed, because they are not applying profile of a surface to a "true profile," which is a foundational rule of that symbol. The diameter of the cone (24 mm or .700) should be basic.

That said, they are the same except that the Genium example has a refinement to the profile -- the FTRZF. I don't know if I'd call it better, but it is more specific if the function requires such a fine-tuning.

For your second question, yes the addition of datum B in the FRTZF seems to be useless. This is because the primary datum A will have constrained 4 degrees of freedom. The 2 degrees not controlled by A would be rotation (irrelevant to what we're doing on the cone) and left/right translation of the entire part -- and this too is irrelevant because by definition the .005 number is only controlling the cone's orientation to the FTRZF's datums (as well as size and form of the cone itself).
IOW, if the cone translates left or right a little bit (that's what datum B would be looking for) then such a movement can only be controlled by the upper PLTZF.

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

 

[greenimi]

Quote J-P
First, I'll keep beating my same drum that both pictures are flawed, because they are not applying profile of a surface to a "true profile," which is a foundational rule of that symbol. The diameter of the cone (24 mm or .700) should be basic.

I agree. 24mm (standard picture Fig 8.18) and .700 (Genium) should be basic.

That's exactly what I have said regarding the picture from OP (Make DIA_5 basic)--see my initial post-- 22 Feb 15 12:20

Thank you.

 

[pmarc]

Hi All,
For what it's worth, I would like to share some thoughts with you about some of the topics being discussed here:

1. In Genium example does B in the lower segment of composite profile callout add any value?
In my opinion it does not. Any rotational degree of freedom that B is able to constrain, has been already constrained by A.

2. Should dia. 24 in fig. 8-18 be basic?
I will take a risk and say that it depends on what characteristics of the cone one wants to control. In most cases it should be basic, but I believe there are situations where basic diameter will not work.

To elaborate a little bit more on this, per current scheme shown in fig. 8-18 profile tolerance controls axial and radial location of the cone relative to datums A and B, orientation of the cone to these datums, and form of the cone. However, it does not control size of the cone. In other words, profile tolerance zone (which is a space between two coaxial conical boundaries) is not fixed in radial size - it can grow and shrink depending on actual size of the circular element located at basic 18 from datum plane B.

Now, what will happen if we change the dia. 24+/-0.2 to basic? We will never be able to accomplish the same effect, because profile tolerance zone (regardless of whether defined by single segment callout, or by composite) will always be fixed in size, thus will never be able to grow and shrink.

3. Has the answer to the original question been provided?
I would say no, because none of the proposed solutions seems to fully capture the functional intent as described at the very beginning. 3 things that need to be addressed are:
- form of the cone to be within 0.1;
- the axial position of the cone in respect to the datum A to be within 1;
- the cone axis to be coaxial to datum B and perpendicular to datum A within 0.05.
Assuming that these requirements are trully functional and that datum features precedence has been thoroughly considered, first thing I have to say is that I don't see a way to decode these requirements using profile tolerance(s) only. If it is okay to keep form of the cone within 0.1, then there is no chance to control position of the cone to B within 0.05 using profile, and not to override the 0.1 form requirement. Something else must be used.

Having said that, my idea would be following:
(a) to leave the DIA._2 as is, if it is acceptable to have size of the cone within [DIA._2 minus e - DIA.2 plus e] limits, OR to change the DIA._2 to basic, if size of the cone can be controlled through 0.1 profile tolerance;
(b) to apply composite profile tolerance to the cone:
- in upper segment |1|A|B| - to control location and orientation of the cone to datums A and B within 1;
- in lower segment just |0.1| - to control form (and size, depending on choice in (a));
(c) (and this is the trickiest part) in order to refine location of the cone axis to B and orientation of the axis to A, to define two additional gage planes close to each end of the cone, apply two diametrical dimensions at these planes without specifing diameter values, and attach two position feature control frames, |pos|dia. 0.05|A|B|, to these dimensions.

What do you think? Would it work?

 

[Belanger]

pmarc -- I agree with most of what you said, but let me pursue Fig. 8-18...
I agree that changing the diameter to be basic will give a different effect, but a more direct question is if it's even legal to have a toleranced diameter.
For instance, take Fig. 5-12. If I change the symbol to profile of a surface, would that be legal? If not, then why is a cone any different (as long as it has one end of the part stabilized as a locating datum)?

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

 

[pmarc]

J-P,
I knew we will get to this

I think this may be a little bit surprising for you, but in my opinion in fig. 5-12 profile with no datum references would be legal. It would do the same thing as cylindricity, but I would not use it exactly because there is much more direct way to express my intent - and that is the cylindricity tolerance.

 

[2JL]

Thanks Guys for your answers.

About the tolerance dimension (again!), because I was aware that it could be in conflict with the profile tolerance, I had always make sure the tolerance value (e) was derived from the profile tolerance as you can see in the attached sketch. Yeeh! No need to do that anymore! Why is there such a thing in the standard at the first place?
[link

http://files.engineering.com/getfil...29b6d6d2&file=Tolerance_dimension_Profile.png

]Link[/url]

Pmarc,
Does the second sketch reflected what you suggested in 3.c? I am not quite sure how well it will work. Since the two additional controls will only apply at the defined locations and not to the entire axis of the cone, the part could be well in spec for these locations but not elsewhere.

Link

2JL

 

[Belanger]

Hi pmarc -- I suppose I am mildly surprised. And not because there is a more direct way to do it (cylindricity). That has never been an issue; if you wish to use profile of a surface without datums to control a single flat surface, then that is identical to flatness. However, you must concede that the nominally flat surface has a basic dimension of zero.

So to illustrate my point, please see the attached graphic. Based on your reply about Fig. 5-12, then you would have no problem with making the diameter of 20 in my first sketch into a ± tolerance. Similarly, you should be willing to allow each of the other pictures to have a ± tolerance on the diameter rather than basic. (Remember, we're talking about what's legal, not what is wise.)

Yet would it really be legal to have the R42 in the last picture be toleranced rather than basic? I think I hear you saying yes, which was the cause for my surprise. (Or if you say no, then the question becomes why the last picture is different from the first.)

Sorry if this seems like a side-track to everyone, but answering this issue in my mind is very integral to the original question regarding how to dimension a cone when a profile tolerance is desired.

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

 

[3DDave]

A nominally flat surface has no dimension associated with it. It does have an idealized shape, just like a cylinder has, or a cone, or a sphere, or a torus. Any of those shapes is either identical to all others (flats are identical to each other) or are scale variants.

If the definitions were properly made there would be no need for flatness or cylindricity. These are forms of profile control which only require the subject profile to lie within two boundaries of given shape, which may have a specific scale associated or not. Runout is similarly a subset of profile.

As far as the poor definitions in Y14.5 are concerned, anything is legal. Y14.5 has been a do-it-yourself kit for a long time. This is seen in the interpretation of figure 8-18, which contradicts the method of interpreting other datum reference frames.

 

[Belanger]

Agreed that Y14.5 is "designed by committee" (literally!), thus leaving holes here and there. So I'm trying to rectify what I see as a contradiction. For profile applied to a simple arc, must the radius be basic or not?

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

 

[pmarc]

J-P,
Yes, you would have no problem with making the diameter of 20 in your first sketch into a ± tolerance (although, like I already said, profile would not be my first choice there), however I do not see a ± toleranced radii working on other sketches. It is simply because ± tolerances applied to radii like these are not standardized/recommended tools, thus open for different intepretations.

2JL,
You are correct, position of the axis (I would actually call it the derived median line) of the cone would be controlled within dia. 0.05 only at the gage planes - I should have mentioned that in my previous reply. In other locations the "axis" would be indirectly controlled by profile 0.1 with no datum references.

One way to have closer control over location of the axis of the cone (if you think this could be an issue) would be to use more gage planes.

I am also thinking about getting rid of all gage planes and associating position FCF with basic angular dimension. But then I would prepare for many questions, because such method is not explicitly shown in the standard.

 

[greenimi]

Pmarc,

My question is what advantages will bring this new method (position FCF associated with basic angular dimension) of tolerancing the cones?

Probably then (with position), MMC’s can be used (if it is functional) , right?

Can we gage these cones, by the end of the day? How many gages? One? Multiple? Or we have to still resort to the CMM for proper inspection?

Thank you

 

[pmarc]

First, one correction in my reply to J-P:
"Yes, I would have no problem with making the diameter of 20 in your first sketch into a ± tolerance (although, like I already said, profile would not be my first choice there), however I do not see a ± toleranced radii working on other sketches. It is simply because ± tolerances applied to radii like these are not standardized/recommended tools, thus open for different intepretations."

The reason I came up with the idea of position FCF associated with basic angle was to have location control of the axis of the cone separated from profile controls in order to satisfy quite unique functional requirements. In general case I think the technique could use MMC's in order to employ surface interpretation of the callout and make verification with hard gage possible, but in this specific situation I don't think the gage would verify these functional requirements properly - we know that the cone may float in location within 1.0 relative to A, and this is not what the gage would verify. I was rather thinking about sole axis/DML position wrt A|B control, thus applied RFS.

 

[Belanger]

Yes, I would have no problem with making the diameter of 20 in your first sketch into a ± tolerance (although, like I already said, profile would not be my first choice there), however I do not see a ± toleranced radii working on other sketches.

Now we're at the crux of it. I don't see how it is logically possible to say that a simple arc needs to have a basic radius for a profile tolerance, but when it becomes a full circle (cylinder/cone) it would suddenly be OK to give the radius/diameter a ± tolerance.

Profile may be used in conjunction with ± tol in terms of relating the surface back to a datum. But I think the curvature of the surface itself cannot get a ± tolerance.

Comments still welcome, but thanks for hearing me out, everyone...

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

 

[pmarc]

J-P,
I am not saying that a simple arc needs to have basic radius because profile tolerance is used. I am saying it needs to have basic radius because the standard does not offer any other unambiguous way to control size of the arc than a marriage of basic radius and profile tolerance. Radius with ± tolerance, unlike ± toleranced diameter, is vague specification, thus subject to different interpretations.

Also, I did not say that for full cylinder/circle/cone radius with ± tolerance would be OK. It wouldn't, again, because the standard does not tell us how to deal with that kind of animal.

If you do not feel comfortable with profile tolerance applied to a circle/cylinder/cone with ± diameter tolerance and you do not see any reason for it, let's use slightly different/more complicated scenario, if you don't mind:
Imagine two parts - one having hexagonal hole, the other with hexagonal pin. The hole and pin are locationally controlled relative to some other datum features. Main functional concern is not only to make assembly of both hexes possible, but also to keep uniform (within a tolerance) gap between both features all around. In other words, it actually does not matter how big/small the hexes are (of course within certain limits) as long as both hexes are precisely controlled for their form and location. How would you encode that requirement using GD&T language?

 

[greenimi]

I remember this discussion on linkedin! Very good solution Pmarc. Even Mark Foster agreed that your proposed solution is better than his own. (BOUNDARY Principle used with Profile Control )

However, I am still not convinced that isn't some sort of conflict between certain statements provided. I know you answered this, but still I cannot wrap my head around it. My brain is not firing up all its cylinders or is not wired properly.
I need more practice (reading it-re-reading it)

 

[3DDave]

The answer to the hex control question - use a note. The symbols available are for frequently used, simple cases. It is far from a general purpose geometry variation description language. If it turns out the requirement can't be put into words, then there isn't a way to substitute symbols for those words. Even if it can be put into words, there may be no symbols that match.

More particularly you are looking at a scaling problem - but that only applies to regular hexagons; other 6 sided convex shapes, irregular hexagons, are not scale variants of each other. There needs to be a symbol for regular hexagons to have a symbolic control based on that shape.

So a note: This pin/hole shall conform to the smallest enclosing/largest expanding right-prismatic surface of a regular hexagon within x.yyyy units as measured normal to each corresponding face. The axis of symmetry of the shape shall be located within a diameter of t.ssss units of the true position. The dimension across the flats of the surface shall be f.gggg+/-j.llll units.

 

[Belanger]

I don't see how the standard is vague regarding profile and its relationship to basic vs. toleranced size/form. Profile is to be applied to a "true profile." But absent an explicit statement saying that the shape must be defined by basic dims, I'll accept that it may be seen as unclear.

Regarding the hex situation, I'm not sure how I would have done it before I read the various suggestions. I think my main inclination would be the same as Dave's: when in doubt, there's nothing wrong with still using a note to describe a specific requirement.

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