Basic Dimensions
Basic Dimensions
(OP)
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?





RE: Basic Dimensions
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Basic Dimensions
A basic dimension will not appeal to any default tolerances. It's closer to a 'reference' dimension than a real dimension in this regard. It is most appropriately used in conjunction with a FCF such as position. If they want to appeal to the tolerance block in the title block or the tolerances in general notes (whichever is applicable) then they need to make it a "live" / "legacy" dimension. Whatever the right name for it is. A plain dimension with no () or box.
_________________________________________
Engineer, Precision Manufacturing Job Shop
Tool & Die, Aerospace, Defense, Medical, Agricultural, Firearms
NX8.0, Solidworks 2014, AutoCAD LT, Autocad Plant 3D 2013, Enovia DMUv5
RE: Basic Dimensions
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic Dimensions
_________________________________________
Engineer, Precision Manufacturing Job Shop
Tool & Die, Aerospace, Defense, Medical, Agricultural, Firearms
NX8.0, Solidworks 2014, AutoCAD LT, Autocad Plant 3D 2013, Enovia DMUv5
RE: Basic Dimensions
Why is that important?
Because a basic dimension can locate a tolerance zone, then the tolerance zone limits the imperfection of a feature's location and/or orientation.
Like someone said here:"While Y14.5's wording doesn't support this nearly as well as I think it should, all explanations of orientation or location tolerances benefit if basic dimensions are thought of as locating and/or orienting tolerance zones, rather than features"
RE: Basic Dimensions
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Basic Dimensions
"Our Engineers will just drop a Basic dimension on the print".... Why are the engineers putting any dimensions on the print? I'm someone that has both a degree in drafting (AS) and in Mechanical Engineering. I can tell you most engineer know hardly anything about drafting. And they definite like to downplay it like there isn't much to learn... which is why its bad news when they start modifying drawings.
But I guess if the engineers are the bosses, basic dimensions are whatever they say they are.
Thanks,
VS
RE: Basic Dimensions
It's 2014. Many design engineers have to know how to use CAD/CAE software in many industries. IMO "drafters" are a dying requirement in many industries. At the least, Designers are required, and in some areas, those will be Engineers. In others they will be wise drafters who know a lot about WHAT they are drafting prints of rather than just seeing 'dumb lines'.
_________________________________________
Engineer, Precision Manufacturing Job Shop
Tool & Die, Aerospace, Defense, Medical, Agricultural, Firearms
NX8.0, Solidworks 2014, AutoCAD LT, Autocad Plant 3D 2013, Enovia DMUv5
RE: Basic Dimensions
That is very true. Unfortunately, it does not detract from the reality of the "most engineer know hardly anything about drafting" statement. As has been posted on this site before - CAD is a tool, drafting is a skill. An engineer may know a CAD package inside out and still produce worthless drawings.
“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV
RE: Basic Dimensions
Tunalover
RE: Basic Dimensions
greenimi gave you the definition of a basic dimension in the same way I understand it. I think it's easiest to envision them as locating tolerance zones instead of locating features. The feature control frame is what tells you the size and shape of the tolerance zone. You never default to the tolerance block or anything else. Otherwise, why make the dimension basic in the first place?
You're doing the right thing by questioning this stuff. You may have to resort to doing things their way just to keep the peace AND your job, but their way is definitely wrong.
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Basic Dimensions
Tunalover
RE: Basic Dimensions
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic Dimensions
tolerance is specified you use Gen. Tolerance as per ISO 2768.
RE: Basic Dimensions
RE: Basic Dimensions
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic Dimensions
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Basic Dimensions
One can not have a basic dim of let's say 3" and consider 4" ok.
On metric drawings the gen. tol. class would be indicates on the info block of the print. Check my link to Maryland Metrics.
Here is from another forum:
Question about a basic dimension without a specific tolerance
Published in February 2nd, 2010
Q – If a basic dimension does not show a specific tolerance what tolerance should be applied?
Elton Hughes
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A – Basic dimensions by nature are a theoretically exact value; however, the feature(s) of a part they define as ideal or exact do need to have tolerances to permit acceptable levels of imperfection during manufacturing.
When a feature is defined with basic dimensions, the tolerance for that feature must be expressed through a geometric tolerance. Most often, the geometric tolerance is indicated directly to the feature or feature of size on the face of the drawing; however, some companies include a general geometrical tolerance (such as a position tolerance or profile of a surface tolerance) in the drawing’s general notes. This can be an effective tool when the note is carefully written.
Drawings based on ISO standards frequently use a class of general geometrical tolerances standardized in ISO 2768-2 :1989. The three classes are identified through the use of the upper case letters H, K, or L after the ISO 2768 indication on the drawing. You would need a copy of the standard to interpret the amount of tolerance available.
If you are absolutely certain that a geometrical tolerance has not been applied to the basic dimension (check all drawing views), then the drawing must be considered as incomplete. Without a tolerance, selecting a manufacturing process for the considered feature is impossible to do with any amount of certainty, and there is no acceptance criteria to compare measurements to during the inspection process.
RE: Basic Dimensions
According to your own post, If a basic dimension does not show a specific tolerance, then the drawing must be considered as incomplete.
What all of that has to do with ISO 2768-1 or -2?
RE: Basic Dimensions
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
RE: Basic Dimensions
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
RE: Basic Dimensions
Anyway thanks for all the input.
RE: Basic Dimensions
_________________________________________
NX8.0, Solidworks 2014, AutoCAD LT, Autocad Plant 3D 2013, Enovia DMUv5
RE: Basic Dimensions
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."
RE: Basic Dimensions
RE: Basic Dimensions
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
RE: Basic Dimensions
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
RE: Basic Dimensions
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.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic Dimensions
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):
RE: Basic Dimensions
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.
RE: Basic Dimensions
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Basic Dimensions
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.
RE: Basic Dimensions