Basic Dimensions 2

[urkson]

I have questions all the time re basic dimensions. Our Engineers will just drop a Basic dimension on the print without any controls. When we question it we are told a. to use the main tolerance control box b. to use the tolerance on the adjacent feature or we get no answer with the 'look' that we should know better than to ask. I do not know if they know how to use the control properly. The problem is neither do I. I think Y14.5 is pretty vague on the subject. Saying a Basic Dimension is the perfect theorectical dimension that can then be controlled, to me, doesn't answer the ultimate question, why use it at all?

 

[Belanger]

juergenwt -- basic dimensions have NO tolerance. This has nothing to do with scale. (Your first statement contradicts the very definition you give under "A" toward the end of your posting.)

The feature linked to a basic dimension gets tolerance, but not the basic dim itself.

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

 

[ewh]

You quoted it yourself... "Basic dimensions by nature are a theoretically exact value".
It isn't the basic dimension that has a tolerance, it is the feature location and is derived from the FCF, not the basic dimension(s). As stated before, if a basic dimension has tolerance applied to it, why make it basic?

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[urkson]

I'm not up to trying to educate our engineers. It's weird we are sent to classes for this stuff and tested annually but the enginering group is not.
Anyway thanks for all the input.

 

[JNieman]

It's weird we are sent to classes for this stuff and tested annually but the enginering group is not.

You said it..

_________________________________________
NX8.0, Solidworks 2014, AutoCAD LT, Autocad Plant 3D 2013, Enovia DMUv5

 

[3DDave]

When only part of the organization is taught something that depends on more parts of the organization to utilize it, that teaching should come out of Marketing budget, because that's the main value for it.

Marketing gets to put in the brochures and presentations that the company trains and tests to support it, but doesn't mention that it's not really used. They won't get up and say - "Our inspectors are trained and tested about 'Y4.5, but they never see it because engineering rarely puts it on the drawings, because we don't train or test engineers."

 

[juergenwt]

Belanger - If there is no tolerance on a basic dim., where than and why would you put a basic dim. on a print as urkson said? Manufacturing can not work to it. Am I missing something? Willing to learn. Juergen

 

[Belanger]

Juergen -- A basic dimension exists to tell you where the tolerance zone is to be located (or angled, etc.). But the basic dim has no tolerance.
The feature linked to a basic dimension gets tolerance, but not the basic dim itself.

It might sound like those two statements are the same idea, but they're not: you can't shorten things and say that basic dims have tolerance, because there are times when a single basic dim can be the "basis" for multiple features, each having a different tolerance.

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

 

[ewh]

Juergen,
The basic dimension is only half of the scheme; you also need a Feature Control Frame, wherein the tolerance is defined.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[KENAT]

juergenwt I went to the effort of digging out ISO 2768-1 1989 (E) to verify I wasn't missing something.

It does not apply for the following dimension:...c) theoretically exact dimensions indicated in rectangular frames

The OP makes it clear that they are talking about dimensions indicated as basic and then for some reason you brought Iso 2768 into the mix even though it doesn't apply per its own text.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[CheckerHater]

Juergen,

As you are "willing to learn", please try and do some learning on your own.

Get a book on relevant standard (ISO or ASME)

The language of the standard books can be quite dry and amount of detail can easily distract, so the next best alternative could be the textbook by respectable author.

As an example I included the fragment from "Fundamentals" of A. Krulikowski dealing with Basic dimensions. Could answer to some of both yours and OP's questions (if they were not satisfactory answered yet):

 

[juergenwt]

CheckerHater - I think we are talking past each other and I think I understand what you are saying. Why a Basic Dim. on a print does not have a tol. listed next to it - it still has a tol. applied to it by a note in the print block. Am I seeing this right?
Coming from Europe you would have a note saying: Dim's without a tol. are as per ISO 2768 etc.(may not be listed because it is common knowledge). Prints in our company in the US would refer you to a tol. table in the print block.
So I guess it is OK to say that basic dim's on a print do not have a tol. listed next to it but must be referenced with the requirements listed in the print block.
If that is not the case - the print is unworkable.

 

[Belanger]

No, no, no... basic dimensions (or "theoretically exact dimensions" in ISO) never appeal to the general ± tolerance shown in the title block. The very purpose of a basic dim is to say "don't use the block tolerances." They appeal to feature control frames (or "tolerance frames," is ISO parlance).

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

 

[CheckerHater]

Dear Juergen,

It seems that you are only reading your own posts.
KENAT already quoted ISO 2768-1 1989 (E): "It does not apply for the following dimension:...c) theoretically exact dimensions indicated in rectangular frames"

So let me add the visual to it. No, ISO 2768 tolerances DO NOT apply to basic / theoretically exact dimensiont and THAT is the common knowledge.

I am a big fan of ISO 2768 myself, but it looks like some users are giving it a bad name. Sorry.

 

[juergenwt]

I guess one is never to old to learn. Thanks guys.