Tolerance Zone of R is ambiguous 3

[tgwow]

ASME Y14.5m, 1994 Section 2.15.1 Radius Tolerance states:

"A radius symbol R creates a zone defined by two arcs (the minimum and maximum radii). The part surface must lie within this zone...."

Section 2.15.2 Controlled Radius Tolerance states:

"A controlled radius symbol CR creates a tolerance zone defined by two arcs ( the minimum and maximum radii ) that are tangent to the adjacent surfaces..."

How do you connect the two arcs? Because no matter how you do it, there's a zone that is zero wide. Wouldn't you need to connect the two arcs with straight edges? And if you did, wouldn't that be the tolerance zone of CR?

What does the tolerance zone look like for R2+-2?

 

[tgwow]

If you examine figure 2-18 carefully, there is no flat (tangent sides) where there should be. It's quite evident that you can see the jagged edges of curvature. Try modeling those dimensions and you can see the flats are quite clearly defined. The flats are large enough to see. Thus, even the figure is ambiguous. I'd say that with close inspection figure 2-18 does NOT include the tangent edges.

 

[KENAT]

1.8.5 Is in effect for any drawings made to ASME Y14.5 unless you have an explicit exclusion.

1.1.4 Is pretty much a get out of jail free card for figures in the standard not being quite complete etc.

That said there do appear to be small flats on 2-18 though due to the line weight of the part contour it's a bit difficult to make out.

It seems like you're trying to play devils advocate and push the 'letter of the law' to the limit. Is there some reason for this?

That said, the fact it stresses tangent for CR but not for R does I suppose make you start to wonder.

KENAT, probably the least qualified checker you'll ever meet...

 

[tgwow]

Kenat,

Remember that CR used to be called Tangent Radius from 1982 so yeah, why?

I think the definitions of the tolerance zones for R, CR and the figures are not well defined enough to say that the tangent sides are included or not. There should be no ambiguity even when pushed to the limit. I shouldn't be able to make the case for not including the tangent sides but I think I can.

 

[aardvarkdw]

I think that what figure 2-18 is trying to convey is that the profile of your radius can fall anywhere within the limits of the tolerance boundary (which incidentally is shown tangent to the edges of the part). The radius is shown exaggeratedly jagged to illustrate the point shown by the boundary lines.

I bet if you took out your caliper and measured the figure the dimensions wouldn't even be correct... see section 1.1.4

David

 

[KENAT]

tgwow, never worked to the 1982 version, so no I don't recall;-).

I don't think there is ambiguity, however there have been areas of the standard discussed before that I find unambiguous but other argue are unclear. From experience I doubt either of us will convince the other.

KENAT, probably the least qualified checker you'll ever meet...

 

[powerhound]

tgwow,
As far as I'm concerned you're not making a case at all. I say that with no disrespect intended. The figures and paragraphs in the standard make it clear what the correct interpretation is and refusal to subscribe to what the standard says does not constitute "making a case" just like making the same point over and over again does not constitute pushing something "to the limit." For lack of a better or nicer term this is just plain being stubborn.

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[tgwow]

powerhound,

Thank you for your response. And I do subscribe to what the standard says.

Let's put things in some context here.
(1) Section 1.8 talks about how to dimension diameters and radius and what the graphics should look like.
(2) Section 1.8.5 says to draw rounded corners using an R dimension and yeah draw it tangent to the sides.
(3) Figure 2-18 conveniently shows a corner. So let's apply 1.8.5. Okay, I can agree with you that Figure 2-18 should include the tangent sides for a corner.

What if the the round is not tangent but perpendicular? What if it's not even a corner? (See attached shapes)
What do you do for those case?

 

[powerhound]

tgwow,
Your new drawing is a totally different animal. We should compare apples to apples. 1.8.5 does not apply to this drawing, 6.5.1 does. 1.8.5 only applies to filleted corners. If it's not a filleted corner then profile of a surface or line should be considered. See Fig. 6-13. It has something close to one of your illustrations. Profile tolerances are what should be used for all of the views you've shown. Everyone got hung up on 1.8.5 because of the first drawing you submitted.

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[tgwow]

Yeah, they're different animals but I'm concern about the "kingdom of animals". I'm concern with a generalization of the whole "kingdom of animals". It's like saying "animals should have legs." The End. So where do the legs go? Enough of that

So the Section 2.15 Radius, where it describes the tolerance zone for R, should apply only to filleted corners?
I thought it was for anywhere you use R+/-.

Again, the tolerance zone of R is ambiguous since R+/- used anywhere else but corners is not well defined.

 

[powerhound]

Now that we're talking about something different than what you originally posted I will address this in a different way.
If we are only talking about filleted corners (as in your first drawing), then the arcs that constitute the tolerance zone must be tangent to the lines that are creating the corner to be filleted. If we are talking about radii that are creating an actual part contour (as in your second drawing), then the tolerance zone is going to be created by the location of the arc, the tolerance of the location of the arc, and the tolerance of the arc itself. In coordinate tolerancing this can be a nightmare but with GD&T the tolerance zone can be fully defined. When you locate the centerpoint or tangent points of the arc and apply a profile tolerance, the zone is clearly defined. You can't just apply an R in this case without specifying where the R is.

Take another look at Fig. 6-12 and 6-13 and tell me if you see anything ambiguous about the way they're defined and if you do, please let me know what it is you're looking at. The R82 and R80 use the tangency rule for "location" as this profile is mathematically defined.

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[tgwow]

powerhound,

I'm completely at ease with Figs 6-12 and 6-13. The tol zones are well defined.

However, I'm not completely sure of how to even draw the tol zones for the simple shapes (for any or some chosen dim scheme with R+/-) I drew. I'm getting the sense that R+/- is not be well defined enough to the point that you'll have to resort to actual profile tolerancing to make it meaningful (excluding corners).

 

[fcsuper]

tgwow,

I don't necessarily agree with your accessment of R. However, if you want to get some traction by bouncing your POV off of individiuals associated with the ASME, join the ASME Y14-5 Yahoo! Group here:

http://tech.groups.yahoo.com/group/Y14-5_User_Group

Good luck.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[powerhound]

tgwow,
From your last post I am starting to think this just may be an issue of not fully understanding GD&T and what the standard really says. Your drawings are completely definable with GD&T with no ambiguity. Please know that I am not putting you down or anything like that but your assessment is unfounded. There will frequently be cases where you have to refer to more than one section to get a full understand of a concept and there are frequently extensions of principle that have to be applied because the standard can't address every single scenario that may present itself. Your drawings do not fall into a category of being difficult or tricky to dimension yet you present them as being so. They are elementary parts that are easily and unambiguously toleranced.


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[tgwow]

Yes, I'm definitely not an expert on the standard. That's why I'm here. I understand that I can define my drawings with no ambiguity with GD&T.

My question is "In general can R be used meaningfully without GD&T?"

So help me out. Pick any one of the three shapes, add your +/- dim scheme and show me the tolerance zone for R. The shapes are simple so this should be easy.

 

[KENAT]

I think that's the point.

Defining many shapes well with just +- dimensions can actually be difficult.

As mentioned I think above, in the case of a rad you typically have both location and size tolerances to be concerned with. Using +- you can end up with either excessively tight tolerances generally to meet the requirement in one area or you end up with excessively loose tolerances if you're not careful.

This is one of the reasons GD&T was developed.

Plus some of your shapes may have more than one possible dimension scheme, depending on end function which is what should drive dimensioning & tolerancing.



KENAT, probably the least qualified checker you'll ever meet...

 

[powerhound]

Now you've added another factor into the mix. This is the first mention of dimensioning WITHOUT GD&T that has been made. I'm at home now so I don't have access to CAD but I can kind of describe something.
On all these parts it's as simple as dimensioning the center of the radius then specifying the radius. This is coordinate tolerancing and the tolerances can really stack up and give you something you don't really want. Not only do you have the tolerance of the radius to deal with, you have the location of the radius to deal with too. You can eliminate this with GD&T by making all the dimensions pertaining to the radius basic. You can also locate the radius with a toleranced dimension and make the radius itself basic and apply a profile tolerance if you want to allow the radius to wander but keep the profile of it controlled.
As I said, I don't see an issue with dimensioning these drawings at all. Specifically what issues are you seeing?
Also see 1.8.2.1 for the rules pertaining to tangency and radii centers and 1.8.6 for the section that would pertain to dimensioning drawing C.

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[Xplicator]

I'm really having a hard time seeing the value in this discussion.
tgwow,
I don't exactly know what it is that you are trying to accomplish here. The shortcoming of the use of the radii "R" callout has been beat to death long before this thread was started. I believe the standards committee is addressing this or at least acknowledging it in the (November 2007) draft revision of the standard. If you have suggestions that are part of a solution rather than continuing to point out your discovery that is already well known. Than pony up the $85 and purchase the rumored next draft and submit your constructive comments for review.

In the mean time use common sense, if the radii has a function that the "R" callout alone does not control and could compromises the integrity of your design, than find another way within the standard to communicate your intent and its function.

This is my last post on this subject/thread unless there is some value to be salvaged from it.

 

[tgwow]

My point is this.

If R+/- is so deficient then it has no place in any drawing except for breaking edges.

I see R+/- used all the over the place without GD&T.

 

[KENAT]

I wouldn't limit it to quite just breaking edges but yes, when using +- it's a bit limited.

To some extent the same goes with chamfers and other faces at other than 90°.

As checker I see all types of stuff on drawings that is open to interpretation, R +/- is often the least of my worries.

I'd say the majority of the people here creating drawings have very little knowledge/understanding or even awareness of these types of issues, the fact that I with limited experience and no real formal training am one of (in top 3) most advanced GD&T users/tolerance analyists in the place speaks volumes.

KENAT, probably the least qualified checker you'll ever meet...

 

[powerhound]

Xplicator,

While there may be no value in this discussion for you, I sort of hope there is value in it for tgwow. I know there are issues with the use of R alone when specifying the rounded ends of slots and obrounds but what is the major issue with using R to specify and tolerance a radius? How would you do it otherwise? Remember the OP was not on the use of R for the ends of a slot or obround nor is it what I have addressed in any shape, form, or fashion, it was for the shape of the tolerance zone for a dimensioned radius.

tgwow,

If this is dragging on and dulling your senses and is proving to be of no value, I apologize.

Powerhound, GDTP T-0419
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Inventor 2008
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