Holding multiple surfaces parallel within 1 common tolerance zone
Holding multiple surfaces parallel within 1 common tolerance zone
(OP)
How do you call-out Parallelism over multiple surfaces that are controlled within 1 common tolerance zone.
Can you simply call-out "x surfaces" under a Parallelism FCF and it's understood that all indicating surfaces are controlled simultaneously (similar to Flatness of multiple surfaces defined by a Profile FCF with such "x surface" notation?
Or would that indicate separate tolerance zones per individual surface?
Or, since I have never seen that example in any ASME standards, is that notation not appropriate when using Parallelism?
Is so, can I simply use Profile instead of Parallelism while referencing a datum and adding "x surfaces" beneath the FCF?
Or is it something else?
Can you simply call-out "x surfaces" under a Parallelism FCF and it's understood that all indicating surfaces are controlled simultaneously (similar to Flatness of multiple surfaces defined by a Profile FCF with such "x surface" notation?
Or would that indicate separate tolerance zones per individual surface?
Or, since I have never seen that example in any ASME standards, is that notation not appropriate when using Parallelism?
Is so, can I simply use Profile instead of Parallelism while referencing a datum and adding "x surfaces" beneath the FCF?
Or is it something else?
Thanks,
Sean





RE: Holding multiple surfaces parallel within 1 common tolerance zone
The other option of using parallelism (with "2 SURFACES" notation) would require each surface to be parallel to the datum on its own terms, but not require the two to be coplanar to one another.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Coplanarity (Profile) is the common way in ASME. Now after 2009, ASME offers another option note: " CONTINUOUS FEATURE" "CF" in a hex symbol, and it would cover you.
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
That was my gut instinct but I'm a little confused about the following.
Reading from my reference chart, "basic dimensioning must be used define the true profile", does this not apply to what you're saying?
Thanks,
Sean
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I'm not sure what yes means. I know what a basic dimensions represent but I'm still confused as to why a basic dimension can't be used in the case mentioned earlier.
Thanks,
Sean
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Yes, it is applied automatically by reference to the ASME standard.
ASME Y14.5M-2009, section 1.4 (k), page 8.
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
The good options to gain the coplanarity and parallelism are to use parallelism with a Continuous Feature modifier, or profile of a surface with a customized datum reference frame that deletes the translation constraint that would locate the features. Either of these tolerances would be placed below a profile of a surface with a larger tolerance zone that controls the location of the surfaces.
I hope this helps.
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Thanks, I know what you are referring to.
But in the case where I do 'not' want to hold the location of the 2 surfaces as tight as the co-planer relationship between each other and the referenced datum, it seems what Belanger has mentioned, would be the only other alternative. This is what I trying to clarify.
Thanks,
Sean
RE: Holding multiple surfaces parallel within 1 common tolerance zone
But the relationship of the true profile to the datum doesn't have to be basic. So that distance is different than the "true profile" itself.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Thank you very much.
Thanks,
Sean
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Leaving the basic dimension between the feature and the datum you are referencing off does not make profile of a surface control only parallelism and coplanarity... It would just mean that a basic dimension is then missing (awol) from the drawing. If you reference a datum feature that is capable of constraining the profile tolerance's location, then the profile tolerance controls the considered feature's location.
I do expect this to create controversy since some trainers in industry have included in their books and training materials, and are to this day telling people that the presence or absence of a basic dimension will affect the control provided by profile... This is not backed up by the standard and as I said in my post above, if this were stated in the standard then this would cause significant issues. I don't think anyone will be able to point out where Y14.5 says that the presence or absence of a basic dimension affects the control provided by profile of a surface. If they can then I will, of course, stand corrected.
Figure 8-27 and section 8.8 of Y14.5-2009 are illustrating and explaining a profile of a line application that I believe can be used well enough to explain one issue. What if this case were for an annotated 3D CAD model with all basic dimension values to be queried from the CAD model? Wouldn't the basic dimension then be "present"? If so, then the profile of a line tolerance zones are located and will stack up to provide the same control as profile of a surface rather than the desired control? Am I the only one seeing a problem will everything shown in figure 8-27..? The control provided should have been achieved in with parallelism of line elements on the upper surface. Even the depiction of the size tolerance limits is not correct, since it incorrectly implies perfect form at LMC.
Either way, nothing anywhere in Y14.5 says that omitting a basic dimension will affect the control provided by profile of a surface. The fact that a profile of a surface tolerance zone is orientation constrainable and location constrainable, combined with the constraint capability of the referenced datum features will determine what profile of a surface will control. That control can be modified by using a customized datum reference frame per Y14.5-2009 sections 4.22 and 4.23, but not by leaving a basic dimension off of the drawing.
This issue is the greatest misnomer regarding GD&T in my opinion. I am very hopeful that the next version of Y14.5 will leave no question regarding this issue. The control provided by a given profile of a surface tolerance dictates the basic dimensions that will be needed, not the other way around.
Regarding the desired control described in the original post, I'm re-stating.. The good options to gain the coplanarity and parallelism are to use parallelism with a Continuous Feature modifier, or profile of a surface with a customized datum reference frame that deletes the translation constraint that would locate the features. Either of these tolerances would usually be placed below a profile of a surface with a larger tolerance zone that controls the location of the surfaces unless something less common, like a size tolerance provided the control of the feature's location.
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
If I understand what you said, above, that is real news to me. I am curious what the last statement in Y14.5M-2009, section 8.2, page 158, means to you? "Where used as a refinement of a size tolerance, created by toleranced dimensions".
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I see several problems with that statement... The profile is not refining "size", so I think that is misstated... In Fig. 8-27 profile of a line is being used to refine the orientation and form of line elements on the top surface... Why would profile of a line be used to do this? Especially now that we have the CF modifier to help with those cases alignment such as coplanarity is desired, and customized datum reference frames to better handle some other more involved part geometry, we don't need profile of a line to be used in this role. What if that top surface happened to be aligned with the origin of the datum reference frame? If so, the basic dimension would be zero, so it wouldn't be shown. Is it then "present" or "not present"?
I think that last sentence of 8.2 describes an odd, unneeded, and problematic application of profile. Since there are problems associated with the notion that the presence or absence of a basic dimension affects the control provided by profile, I think Fig. 8-27, Figs. 8-17, and 8-18 sections 8.2, 8.8, and maybe some other items need some rework. Without explicitly stating it, they tend to imply that the presence of absence of a basic dimension affects profile. Due to the problems associated with that practice, I don't ever use profile that way and my opinion is that we should firmly shut the door on that practice. There is some implied justification of the practice, but we have other tools that accomplish what is needed without the zero basic and queried CAD body problems.
When some of these things are cleaned up a bit, maybe this will all be not as much fun..?
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Please don't mistake me; I am not a fan of toleranced dimensions, by any stretch. We are still actually using 1982 at work, I don't have "CF" and the other options, even composite profile is a new concept for most around me. I really think we are in danger of making the standard more irrelevant to the real world, particularly, if we can't trust what is shown and written in it.
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
First, just because the standard doesn't explicitly state or show the precise example being analyze, that doesn't mean that we can't venture into that area. Recall that GD&T is a language, and we can use the building blocks of the language to create a control for any conceivable design, as long as we don't violate an obvious rule of the language.
Second, why it is so problematic to use profile without a basic distance to the datum? Fig. 8-27 obviously does such, so why attempt to explain it away? There is a valid point in mentioning the CAD model, which would obviously be a basic dimension. If we wish to unlock the location aspect of profile, however, then we simply display a toleranced dimension on the height. Problem solved! You stated that parallelism should have been used, but what if the top is a curved surface by design? The only option would of course be a profile control.
Third, we have the descriptions given in paragraph 8.2. You dispute that profile is a refinement of "a size tolerance created by toleranced dimensions," but realize that it does refine the orientation portion of the size tolerance. A refinement does not mean that every aspect of the original control must be trumped -- consider how a FRTZF is a refinement of a PLTZF.
Here's the best way to think of it: Profile is, at heart, a form control. If we take Fig 5-7 and simply use the profile of a surface symbol instead of flatness, it would have identical meaning.
But, if desired, profile can be elevated to the next level of the GD&T hierarchy, which would be orientation -- if we take Fig 6-2 and simply use the profile of a surface symbol instead of parallelism, it would have identical meaning. (Apparently, this is where you disagree?)
Finally, if desired, profile can be elevated to control location. That is the only way to control location of a surface, but I'm saying that we shouldn't insist that profile is incapable of doing those intermediary levels of control (orientation), if that is what the function requires.
This has been discussed before on the forum, but it boils down to this: is profile best described as a lower-level control that can be promoted to higher things? Or should it be described as a higher-order control that can be lowered by omitting things? Using logic, wouldn't the first idea be the only way? I can tell you that I live in the US (a low-level piece of information), and that means that I could be in Texas, Oregon, or Illinois; you don't know. But if I say I live in Chicago (the highest-order piece of information), you immediately know that I live in Illinois and that I live in the US. The only common information between them is the country. So the information I give is, at its heart, the country. If I so choose, I may elevate the information to give you more detail.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I have a copy of a GD&T Pocket Guide created by a very well-known GD&T instructor, and it drives me nuts that the symbols table on the front cover shows profile as a "location" control, alongside position.
As I tried to show, profile may control location, but it is incorrect to present profile as location control by its very nature. (I don't think anyone in this thread has claimed that, but I'm just illustrating the "middle ground" capability of profile, lying between form and location.)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I am glad that you mentioned directional datum controls as an option; I had not actually thought of that approach, it does seem an overly complicated solution. The use of "CF" (if allowed on non-FOS, which seems accepted here but is not really clear in the text of the 2009 standard) is the easy solution. Even using composite profile would be radical in my world. In the world I am from, people do not see/understand the problems with "implied tolerance dimensions" that people here, and the standard committee, are very concerned about.
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Leaving a basic dimension off a drawing to change what profile will control is a method that may be implied in Y14.5, but it has never been explicitly and clearly stated. This is a method that can be applied in specific, simple cases but that does not make it a robust method.
Please see the attached file.
There are better ways to specify the type of control the OP (Sean) is after. We don't need to implement a problematic method to provide the desired control.
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Dean
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Your slides raise some good points, but they are points that exist for those examples. That is not evidence to discount the entire notion of using profile together with toleranced location dimensions!
For slides 1, 2, and 5, yes there is an issue with the sideways location. But I could draw an example where the surface could be located in horizontal and vertical directions with adequate ± tolerances, and there would be no issue. So I think your complaint is really with a dimensioning method which can cause problems for profile. It isn't with profile as an orientation control.
I agree completely with you on slides 3 and 4. But these situations shouldn't happen because they violate paragraph 8.2, which requires profile to be applied to a true profile (basic dimensions for the shape).
So again, I'm not discounting your points. But they are for situations external to the nature of profile, not to profile itself. IOW, we we can't say that profile must always have basic dimensions to tie it back to the datums just because of a few ambiguous scenarios, which seemed to be your underlying thesis.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
A true profile is more than just basic dimensions to define the shape of a feature. To complete a true profile basic dimensions to orient and locate the tolerance zone based on any constraint the datum features provide are also needed. You wouldn't say that true position is complete if one basic dimension is deleted from those needed to orient and locate a position tolerance zone would you? Why should true profile be any different?
Y14.5 implying that the absence of a basic dimension for location makes profile a form and orientation control is only done when combined with a size tolerance... Now you're bringing directly toleranced location dimensions into the picture. Directly toleranced location dimensions are ambiguous, since the direction of measurement is not defined and no standard describes a tolerance zone for the practice, so all you really have are two point measurements from one place to another. A combination of profile and an ambiguous location dimension might work on some simple parts in some environments where things are done by known people, but it's not a practice I would want to advise anyone to use.
I'm confused by what you say about the issues pointed out being valid, but not convincing since for other examples you wouldn't see such a problem... Shouldn't the methods of a good tolerancing system work equally well for all eligible applications?
I did expect some disagreement regarding the issues I am pointing out. I understand that the notion I am working to dispel is a firmly entrenched one for many people. We will probably end this cordially agreeing to disagree.
The good tools we thankfully now have are the CF modifier and customized datum reference frames. These two items in our "tool box" enable us to provide desired controls without engaging notions like leaving basic dimensions out of a true profile. If we could just have a modifier for profile to make it truly a general form control, instead of having a fixed geometry (shape) tolerance zone, then we would really be in a better place. Then we can have a form refinement of a non-round or non-flat feature with a profile tolerance zone that really does behave just like a form tolerance (as long as we're careful about simultaneous requirements). I think that modifier would be a good addition to a future version of Y14.5.
Best Regards,
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Why? Because of the first sentence of paragraph 8.2: "A profile is an outline of a surface, a shape made up of one or more features, or a two-dimensional element of one or more features." Notice that a profile is at minimum just a shape; there is no mention of any relationship to other things.
And of course, simply adding the word "true" means that we must use profile on a perfect, theoretical shape. (But not necessarily a perfect, theoretical location.)
If we desire to constrain it to datums for orientation or location, then that goes beyond profile's intrinsic purpose (which is fine), and the third sentence says that profile may or may not be related to datums.
I do agree that the all around/all over stuff as well as CF and customized DOF help improve the language for certain situations.
Also, my statement about a point being valid for a specific example but not necessarily for an entire concept troubles you :)
Well, let's go back to Fig. 8-27. I agreed that your examples had some issues with ambiguity on the location of a surface. But 8-27 does not. That's proof that a statement about one drawing doesn't equate to a blanket statement for the entire concept.
All in good fun, right? What a way to spend a Saturday evening :)
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I also wonder about the statement that Dean mentioned. He stated "Directly toleranced location dimensions are ambiguous, since the direction of measurement is not defined and no standard describes a tolerance zone for the practice, so all you really have are two point measurements from one place to another." I know other individuals with design background have also mentioned the 2 point measurement approach but Fig. 2-5 in 2009 does not support that concept. It does reflect a tolerance zone on a surface. Besides, love to see how someone could measure the surface using 2 points.
Dave D.
www.qmsi.ca
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Fig. 2-5 is for Dimension Origin. I thought it would be clear enough that the directly toleranced location dimensions I was referring to as ambiguous were not those using Dimension Origin. Dimension Origin is essentially the same as a profile of a surface, so of course there is a tolerance zone when using dimension origin.
Combining directly toleranced dimensions (which are ambiguous) with profile is not a good practice.
Since there are ways to accomplish the control shown in Fig. 8-27 that don't have the issues associated with them that combining profile with directly toleranced dimensions does, why wouldn't we all just use the methods that are not problematic?
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Combining profile with toleranced dimensions, in that case, has no issues that I can see.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
The problem with Fig. 8-27 is that it uses a method that is contrary to a logical tolerancing system. To be logical, the types of geometric control that profile provides would be based upon the fact that it imposes a location constrainable tolerance zone combined with the constraint capabilities of the referenced datum features. If we want to release any of those degrees of freedom, as is desired in the case shown in Fig 8-27, then we can use the customized datum reference frame method described in sections 4.22 and 4.23.
To have one exception that allows a basic dimension to be replaced by even a valid size tolerance (one that is applied to a valid feature of size, as in Fig. 8-27) would be an odd and unnecessary thing to do, within the logical approach that I prefer to stick to.
I hope the slides I posted on April 28th show well enough why the presence or absence of a basic dimension affecting what profile controls would not always be clear.
A even more simple reply to the problem with Fig. 8-27 could be "Why isn't parallelism of line elements on the upper surface of the part specified instead?"... Wouldn't that be a lot simpler? For cases where that upper surface was more complex then profile with a customized datum reference frame could be used.
Of course Fig 8-27 is part of the standard, so the method shown there can be used... I just wouldn't recommend that approach since I think there are better ways to accomplish the same thing.
Best Regards,
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Allow me to jump into discussion just for a moment and share a thought or two.
I am rather with J-P on the debate about fig. 8-27, meaning I do not see significant problems with it. Agree, the same goal could be achieved by at least two different methods, like Dean pointed out, but in my opinion that does not mean the third option is vague. As we all know and very often repeat, GD&T is a language, and like in any language there are multiple ways to express the same intent. Some ways fit better to certain situations (applications), while others work fine somewhere else. I think we face such situation here.
Dean, a question to you: as you already emphasized couple times in this thread the availability of customized datum reference frame tool, why couldn't we for example get rid of composite positional tolerancing and use two or more single segment positional callouts with customized datums in lower FCFs instead? Wouldn't it be the equivalent way of expressing the same design intent? Like in composite tolerancing, lower FCFs would only control spacing within the pattern and/or orientation of the pattern relative to referenced datums without having translational DOFs contrained. If you agree they are equal, wouldn't it be reasonable to forbid composite and really help those folks who have serious difficulties in grasping the difference between composite and multiple single segment posistional tolerancing? Wouldn't it simply make Y14.5's GD&T more consistent?
RE: Holding multiple surfaces parallel within 1 common tolerance zone
The real problem I see, and constantly stress here all the time, is the detachment of the philosophy and direction of the standard from the reality of the real world. Am I the only one who sees this? Are the companies I work with that far behind?
According to this thread:
thread1103-321252: Functional vs. Process Driven GD&T there are still people who shun GD&T altogether.
I agree that the spirit of the standard according to its own "Foreword" is in line with where Dean is going. I just think it has left the real world way behind and becomes in danger of being irrelevant. People here say they avoid it at there own peril, but, actually for the most part they do pretty well and seem more than willing to take the chance. This is if I judge by the actual actions of the companies and not what people here say!
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I am shocked, shocked that someone would disagree with me :)
It seems you're making this harder than it should be, what with customized DOF, etc.
But I challenge a broad assumption that you are making:
"To be logical, the types of geometric control that profile provides would be based upon the fact that it imposes a location constrainable tolerance zone combined with the constraint capabilities of the referenced datum features."
Why should profile be "location constrainable"? Profile is capable of controlling form, orientation, location, size, or a combination of those things. You seem to jump right to location, but form is actually the only one in that list that is a requirement (assuming that there is no T modifier).
Could we take Figure 6-2 and replace it with profile of a surface? I am hearing from you that this would not be logical, since it lacks the location aspect.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I said location "constrainable", not location "constrained".
What you call a broad assumption includes no assumptions..? It is a statement that I believe if free of assumptions.
I would never apply profile of a line to accomplish the the same thing that parallelism of line elements could accomplish, so I think anyone arguing that Fig 8-27 shows a good practice is making things complicated. I would use profile with a customized datum reference frame only if the upper surface of the part were not a planar surface.
Fig. 6-2 shows a figure with the entire upper surface of the part having its orientation and form refined with a parallelism tolerance. That seems fine to me. The size tolerance also applied in the figure seems likely to be OK too. One could question whether the features included with the size tolerance constitute a valid feature of size, since the two surfaces are not fully opposed (one being smaller than the other), but I believe the design engineer needs to decide whether a feature such as this should be considered a feature of size. Somewhere between fully opposed and fully offset, the feature must transition from a feature of size to one that is not a feature of size... The line where that transition occurs needs to be determined by the design engineer, I believe.
Frank,
Your concern about the acceptance of GD&T and whether Y14.5 and other Y14 standards are becoming less relevant as they are developed further is valid for sure. We're all in an odd state where ambiguous specs are often tolerated by industry, the quality of measurement data is often low, many in the academic world view GD&T as "too easy" ("it lacks academic rigor", I've been told) and a drafting or manufacturing subject that isn't worthy of adequate coverage in their mechanical engineering curriculum, while industry views GD&T as "too hard" ("if I put that on the drawing no one will understand it"). There are things we could do to simplify the language a bit, such as reducing or eliminating the need to calculate where boundaries are. We could instead allow direct statement of the location and type of tolerance zone boundaries. We could clarify the orientation of line elements or cross-sections with more explicit notations.
We could also have some sort of certification for metrologists. Having an ASME GDTP certification may help a metrologist, but what about the need to iterate to establish a repeatable datum reference frame with a probing CMM, the need to verify repeatability of data in a standard way, and when and how to properly design fixtures to restrain parts for measurement.
Overall, I see "Mother nature" as the entity that requires the level of complexity in GD&T... Dealing with imperfect geometry in an explicit and complete way is not so easy (as most of those reading this know). I think especially upper level managers will always need convincing with regard to the need for GD&T in order to optimally design and produce physical products. Measuring a part with a pair of calipers seems so simple to them. I haven't encountered an electrical engineering subject which would be viewed as something that can be simplified to the point that someone stepping in off the street should be able to understand it. Our mechanical engineering subject of GD&T suffers from the apparent simplicity of "dimensions", I believe. Some academics and some managers in some industries "get it". When we can say that most "get it" then we will be past our current state of affairs & in a better place, I hope.
Pmarc,
Yes, I think two single segment feature control frames with position or profile could replace composite feature control frames. They're almost equal, except for how simultaneous requirements works (with "SIM REQT" being required to tie together patterns that are toleranced with separate composite feature control frames... no such need with a set of single segment feature control frames). Customized DRFs are better since they more explicitly state what they mean than composite FCFs do, and the method is also more flexible/powerful since even rotational degrees of freedom constraint can be selectively specified using the customized method... I will create a couple of examples and ask in a new topic what others think of setting aside composite in favor of customized. It makes sense to introduce customized drfs before composite would be set aside, but I don't know what is best with regard to the overlap time, when both are available in the standard.
Best Regards,
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I thank you, and others here, for my contiuning education in this subject. Nice presentation, too.
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
If we want a planar surface to be parallel and not constrained with size, sure, we can use parallelism. But if the surface is curved, we can simply swap in the profile of a surface symbol; this is the crux of my argument. There is no need to mess with customized DOF.
Profile controls form, orientation, location, and/or size. To understand which aspects are being controlled, we simply look at the given parameters:
Is the profile "all around"
Does it reference datums?
Is it tied to those datums with basic or toleranced dims?
Answering those and other questions will easily settle the question of which aspect(s) a given profile tolerance is controlling.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I know I will have many drawing errors out there if it doesn't break your way. The dilemma I see is drawings must get done day to day and cannot wait 10 more years, for decisions on this stuff. It is shown in books as Dean has mentioned, the company book I wrote has this concept in it. I am not saying that things can't be changed, but, it really puts us, out here in the trenches trying to fight the good fight, in a tough spot.
Frank
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Q: How to control 'multiple planar' surfaces co-planer to each other and parallel to a referenced datum while not constraining with size. (re-worded a bit)
Are we at least in agreement that the proper way to do this is with a profile FCF, using a datum reference and with notation stating "X SURFACES"...?
However this thread has been quite entertaining :)
Thanks,
Sean
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Frank, I completely agree with your concern. I too am in the trenches of GD&T application and then at least a close observer of subsequent measurement data gathering and reporting.
The issue I thought was worth bringing up here isn't so much a problem when a dealing with a feature of size, as in Fig. 8-27, but we all know that misconceptions regarding that figure are very likely, such as thinking the practice can be extended to mixing profile with directly toleranced dimensions that are applied to a set of surfaces that are not a feature of size... Those specs are ambiguous, so then we're in a mess of having a spec that can be interpreted in more than one way by inspection.
I am all for simplicity as long as we can have it without significant risk of ambiguity... If tolerances are loose enough then maybe some ambiguity, like in one of those instances that someone applies a directly toleranced "location" dimension (excepting dimension origin, so therefore an ambiguous location tolerance), can be OK (call it "bonus uncertainty"
I've had very knowledgeable, well accepted GD&T trainers tell me that profile applied to a cylindrical feature with the basic diameter replaced with a directly toleranced diameter dimension will have a tolerance zone that expands or contracts in diameter, just like cylindricity... That is not correct, but it is an extension of the impression that people take from Fig. 8-27 and a couple of others.
We can all only work to the standard we have, and Y14.5, and especially its 2009 version, is the best GD&T standard, in my opinion. Even then I prefer to choose what I think are the best methods available within Y14.5 and avoid the ones that I have seen cause problems. As the standard advances I hope the problematic methods are reduced and deleted and robust,useful, and, as much as "Mother nature of mechanical parts" allows, simple methods are added.
Best Regards,
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Sorry for another off-track post... I didn't see yours as I was writing that one.
I think profile with a "nX", where n is the number of surfaces would be best.
You will notice that "x SURFACES" no longer appears in Y14.5 as of the 2009 version (unless I'm mistaken). See sections 1.9.5 and 1.9.5.1 in Y14.5-2009. The issue with having "nX" and also "n SURFACES" is that people would tend to believe that their meaning was different, or that each should be used for specific situations, but not in others. There never was a specific difference in their meaning or application, as far as I know.
The only place I recommend the use of the word "SURFACES" is for the "(n SURFACES)" notation I think should be added as reference information (so in parenthesis) with a <CF> modifier.
If you are running into opposition to profile, of if you think it is a more intuitive spec for less educated suppliers, then a single Flatness tolerance with <CF> (n SURFACES) is an alternative to control coplanarity and form.
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
Dean, I must get in one final response, though...
We both agree that profile of a surface on a cylinder would require a basic diameter, rather than a toleranced diameter. But it's not for the reason that you give. It is because profile must be applied to a "true profile" -- a profile where the shape itself is basic. And Fig. 8-27 does have a "true profile" (a flat surface is implied as zero millimeters of curvature). You're focusing on the fact that it doesn't have a "true location" to the datums. But that is not a problem, and it doesn't correlate to the cylinder example.
OK, now I'll exit stage left...
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
As I have already said, Fig 8-27 is part of the standard, so the method shown could be used. Should I have written that in all CAPS?
I've also said several times that it unnecessarily shows an application that leads to misunderstandings and ambiguous applications in other cases. It does not point out that the method shown is only valid if the directly toleranced dimension is a valid size tolerance, and that this method works only with the one simple case shown (the feature could be internal or external, but must be two opposed parallel planar surfaced). Again, as I've said several times, there are better ways to accomplish the control shown and those methods can be extended to other types of features.
Dean
www.d3w-engineering.com
RE: Holding multiple surfaces parallel within 1 common tolerance zone
"Yes, I think two single segment feature control frames with position or profile could replace composite feature control frames. They're almost equal, except for how simultaneous requirements works (with "SIM REQT" being required to tie together patterns that are toleranced with separate composite feature control frames... no such need with a set of single segment feature control frames). Customized DRFs are better since they more explicitly state what they mean than composite FCFs do, and the method is also more flexible/powerful since even rotational degrees of freedom constraint can be selectively specified using the customized method... I will create a couple of examples and ask in a new topic what others think of setting aside composite in favor of customized. It makes sense to introduce customized drfs before composite would be set aside, but I don't know what is best with regard to the overlap time, when both are available in the standard."
I am wondering how likely to show up in Y14.5-Next. Does anyone know?
I look forward to the topic you plan to post, Dean. 'Thanks', in advance.
Peter Truitt
Minnesota
RE: Holding multiple surfaces parallel within 1 common tolerance zone
I will put some examples together and post my question about what others think of customized DRF tolerances being used in place of composite feature control frames, but it may be another 7 weeks or so until I get that done. Spare minutes between now and the end June will be hard for me to find.
Dean
www.d3w-engineering.com