## Tolerance Zone of R is ambiguous

## Tolerance Zone of R is ambiguous

(OP)

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?

"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?

## RE: Tolerance Zone of R is ambiguous

R; Flats and reversals allowed

CR; Flats and reversals not allowed

Chris

SolidWorks/PDMWorks 08 2.0

AutoCAD 06/08

ctopher's home (updated 10-07-07)

## RE: Tolerance Zone of R is ambiguous

Powerhound, GDTP T-0419

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## RE: Tolerance Zone of R is ambiguous

How could the tol zones be the same when CR requires tangency and R does not? The tol zones in the figures in ASME for R and CR appear the same but are they really the same? Try drawing it for the example of R2.4 +/- .3 from ASME. Because the arcs aren't require to be tangent, the zone can move anywhere between the tangency point of the minimum radius and the sharp and you still satisfy the definition of R. (See attached pdf)

powerhound,

This may seem silly but it is fundamental in understanding what R means. So, is it possible to draw the tol zone of R2 +/-2 using the ASME definition?

## RE: Tolerance Zone of R is ambiguous

Matt Lorono

CAD Engineer/ECN Analyst

Silicon Valley, CA

Lorono's SolidWorks Resources

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## RE: Tolerance Zone of R is ambiguous

Regarding your drawing; the arcs are required to be tangent per 1.8.5 and 1.8.6 of the standard but not tangent to each other, they must be tangent to the corner that they are supposed to fillet. You would draw the minimum arc tangent to the edges of the corner and then the maximum arc tangent to the edges of the corner. The bottom view of your drawing is correct.

Regarding the "silliness" comment; what I meant was that if a sharp corner is acceptable then why even put a radius there? It's just one more thing that QC will have to inspect. The tolerance zone for a 2 +/-2 will look like a triangle with one of the legs as a 4 radius.

Powerhound, GDTP T-0419

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## RE: Tolerance Zone of R is ambiguous

Section 1.8.5 and 1.8.6 requires that the actual part geometry be tangent to the sides but says nothing about the tolerance zone.

Therefore, why would you draw the min and max arcs tangent for R? Additionally, the definition of the R tolerance zone does not state inclusion of the tangent sides as boundaries.

By definition, wouldn't the tol zone for R2 +/-2 be just the max arc (since the min arc of zero just disappears) located somewhere in the corner (not required to be tangent)?

## RE: Tolerance Zone of R is ambiguous

Depending on the application the 'silliness' point about why even break the edge may have merit.

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

## RE: Tolerance Zone of R is ambiguous

We're kind of going on a tangent but for parts which are molded I've seen requests from suppliers who would want the CAD model modeled at nominal which would mean in order to "show" the dimension from the model on the drawing for "R4 MAX" and keep it parametric, "R2 +/-2" would be prefered over "R4 MAX".

The alternative is to model at R2 then fudge a dimension "R4 MAX" on the drawing.

## RE: Tolerance Zone of R is ambiguous

I'm always tempted to tell those suppliers that if the drawing is the master then the model is for reference only and maybe they'll actually need to do some work and go in and modify things.

The trade off between the possible extra cost of this compared to the impact of worrying about the kind of issues modelling strictly nominal (as in mid range with unilateral tolerances) cam cause need to be weighed.

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

## RE: Tolerance Zone of R is ambiguous

The same technique can be used for asymmetric tolerances like shaft & clearance holes where the tolerances are both positive or negative. The dimension can read 1.000+.005/+.001 and the model will measure 1.003. You can also set the dimensions to regenerate at the maximum or minimum value to do tolerance stackups. The state of the dimension (max, nominal, middle or min) is indicated by color.

## RE: Tolerance Zone of R is ambiguous

## RE: Tolerance Zone of R is ambiguous

There is really nothing more I can add to clarify this any further. I hope this is good enough.

Powerhound, GDTP T-0419

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## RE: Tolerance Zone of R is ambiguous

Thank you for your responses.

Extending the principle based on 1.8.5 and 1.8.6 does seem appropriate and reasonable as an implication. However, I still think my original premise is still true due to the deficient definition in the standard. The tolerance zone for R is ambiguous as defined in the standard. Therefore, the only practical use of R that I can see is to indicate a break edge.

## RE: Tolerance Zone of R is ambiguous

Yeah, I can see other uses for R as well, but one of the bigger uses is to break edges.

I've noticed that a lot of people do not understand radius symbols. I had one boss years ago who questioned me every time I used SR (spherical radius) per the standard. The conversation used to go like this:

Boss:"You have a typo here on your drawing."

Me:"That's not a typo. It is a spherical radius."

Boss:"What's a spherical radius?"

Me:"I'm dimensioning this spherical radius with the spherical radius symbol."

Boss:"I've never seen that before" ::looks at me like I'm making things up::

Me:"It's the standard since 1994."

We had this conversation twice for separate revisions the same drawing. Then one day, we was changing the drawing for some other reason and then removed the S from SR on the SR callout.

I didn't throw it in his face. I just simply added the S back on the next revision. He stopped bugging me about it after that. However, this likely drew out so long because we didn't have a copy of ASME Y14.5M in house at the time. (as this for hijacking a thread? )

Matt Lorono

CAD Engineer/ECN Analyst

Silicon Valley, CA

Lorono's SolidWorks Resources

Co-moderator of Solidworks Yahoo! Group

and Mechnical.Engineering Yahoo! Group

## RE: Tolerance Zone of R is ambiguous

As to “What does the tolerance zone look like for R2+-2?” based on 2-18 isn’t it something like my attachment, or am I missing something?

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

## RE: Tolerance Zone of R is ambiguous

Production Supervisor

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## RE: Tolerance Zone of R is ambiguous

The problem with your sketch is that the definition doesn't say use MIN R, tangent lines, and MAX. It just says to use MIN R and MAX R. Additionally, the MAX R arc doesn't have to be tangent to the sides so you can move the MAX R arc towards the corner and tilt it.

Even if we make the assumption that you can use the tangent sides, the MAX R arc doesn't have to be tangent to the sides so you can move the MAX R arc all over the place as long as it intersects the sides. Therefore, the tolerance zone for R is not well defined at all.

## RE: Tolerance Zone of R is ambiguous

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

## RE: Tolerance Zone of R is ambiguous

Agreed. Arcs are to be tangent. That is clearly stated in the standard. See Fig. 1-29 which is referenced to in 1.8.5.

Production Supervisor

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## RE: Tolerance Zone of R is ambiguous

## RE: Tolerance Zone of R is ambiguous

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...

## RE: Tolerance Zone of R is ambiguous

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.

## RE: Tolerance Zone of R is ambiguous

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

## RE: Tolerance Zone of R is ambiguous

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...

## RE: Tolerance Zone of R is ambiguous

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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## RE: Tolerance Zone of R is ambiguous

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?

## RE: Tolerance Zone of R is ambiguous

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.

Production Supervisor

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## RE: Tolerance Zone of R is ambiguous

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.

## RE: Tolerance Zone of R is ambiguous

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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## RE: Tolerance Zone of R is ambiguous

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).

## RE: Tolerance Zone of R is ambiguous

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: h

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

## RE: Tolerance Zone of R is ambiguous

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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## RE: Tolerance Zone of R is ambiguous

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.

## RE: Tolerance Zone of R is ambiguous

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...

## RE: Tolerance Zone of R is ambiguous

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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## RE: Tolerance Zone of R is ambiguous

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.

## RE: Tolerance Zone of R is ambiguous

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.

## RE: Tolerance Zone of R is ambiguous

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...

## RE: Tolerance Zone of R is ambiguous

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.

Production Supervisor

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## RE: Tolerance Zone of R is ambiguous

On the contrary, this has been extremely valuable.

My major issue is this:

If it's difficult to show the tolerance zone of R+/- then wouldn't it be difficult or even next to impossible to verify that your parts are good? Thus, using R without GD&T is no good in practice.

GD&T should be used 99.99% of the time instead of just R+/-

And yes, the original OP which was a starting point has been addressed (Thank you all).

However, to have a better understanding I needed to close all the related issues.