Question about ISO_13920
Question about ISO_13920
(OP)
It is possible to make a welding drawing of the item in the picture without adding any measurements, (if you have drawings on details 1 to 4), because the items is aligning with the edges of item 1. So what I wonder is who I shall interpret the general tolerance concerning distance in this case, because the distance is 0 from the edges.





RE: Question about ISO_13920
However real parts will have deviation from nominal, and therefore not all the edges will line up perfectly.
You need to add dimensions to define what to do with real parts when they don't line up perfectly.
RE: Question about ISO_13920
RE: Question about ISO_13920
It all starts with the function. You have to figure out which tolerances will make your part work. Then you compare them with ISO 13920 tolerances. If ISO tolerances are acceptable, you specify them on the drawing. Your part may require tighter tolerances, and then you’ll have to specify them on the drawing in addition to ISO tolerances or instead of them.
It is possible that part could be produced cheaper but will function well with some tolerances being larger than ISO 13920. In this case larger tolerances may be specified on the drawing as well.
No, 0 inch/mm, 0 degrees, 90 degrees and so on are usually implied and not specified on the drawing.
Nevertheless it doesn’t mean your drawing shouldn’t have any dimensions whatsoever.
Your dimensions specify how your part looks and works after being assembled.
So, position of center of your round element may be important. It affects assembly with other parts.
Some companies require specifying envelope dimensions, especially for large heavy parts – it affects packaging and transportation.
At the end of the day you are the boss – you know how your part works and it is your goal to produce the drawing the way that nobody will come back to you to ask questions.
Good luck!
RE: Question about ISO_13920
But of course the way you describe it is the correct way to do it, but sometimes you are not the king of the circumstances.
RE: Question about ISO_13920
As long as the variation from ideal that is produced by your fabricator is smaller than the application has tolerance for, there will be no motive to change. It is only when items that meet all the drawing requirements fail to fit or function that there is a need to change the drawings.
RE: Question about ISO_13920
In other words: ISO 13920 codifies exactly what happened before ISO 13920 existed.
Basically "Line 'er up as best you can and weld the sucker"
So in effect specifying "Tolerances per ISO 13920" is functionally the same as specifying no tolerances at all.
It just makes you feel good because "I called out a standard."
RE: Question about ISO_13920
"Non conformities
A decision on the acceptance of components not complying with this standard may be made on the basis of the suitability for their intended purpose."
RE: Question about ISO_13920
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Question about ISO_13920
i hope this isn't a stupid question.
RE: Question about ISO_13920
RE: Question about ISO_13920
The picture with actual geometry shows incompleteness of the weldment drawing pretty nicely. The fact that the drawing shows two plates aligned to the left does not automatically mean they will always be welded this way in reality, thus the drawing should clearly specify the maximum amount of misalignment allowed. This value, which is a locational tolerance, can't be found in ISO 13920 (according to the second paragraph in clause 4.3).
That is why I don't think Clause 7 should be used to say that manufacturer made an error or not. Regardless of whether we like the wording (and presence) of the clause or not, it applies when actual geometries of welded parts do not comply with the content of the standard. However, since the standard defines no general tolerances for location, there is nothing to comply with with regard to this characteristic.
So did manufacturer make an error? No, he did not. He delivered part satisfying all requirements defined on the weldement drawing (assuming that the measured distance was 10+/-0.5, not 10+/-1). It is not his fault that the requirements were poorly defined.
RE: Question about ISO_13920
RE: Question about ISO_13920
RE: Question about ISO_13920
I am talking about OP drawing showing dimension 10±1. It's linear dimension (it isn't angular, is it?) and linear dimensions are covered in Para. 4.1 and Table 1.
How come ISO 13920 "defines no general tolerances for location" then?
RE: Question about ISO_13920
As for 10±1 dimension, this dimension is not on the drawing posted 22 Mar 14 12:30, so I do not understand why you want to apply general tolerance from Table 1 to it.
RE: Question about ISO_13920
On OP's drawing vertical part is shown aligned with the edge of horizontal part.
The fabricator produces part where vertical part is 10 mm away from the edge.
OP believes it should be 0 (within some tolerance)
What all of it has to do with position and profile?
RE: Question about ISO_13920
If two surfaces are shown coplanar, like on OP's drawing, is it enough to just show them like that and do nothing more, or should there be an additional tolerance specifying how much off the coplanarity these two surfaces are allowed to be? If I want to use geometric tolerances for that (because I believe that linear dimensions are ambiguous, and because I know that Table 1 in ISO 13920 does not give me general tolerance for linear dimensions less than 2, what should my first choice be? Since I work to ISO, I am choosing between position and profile (they basically mean the same according to that standard). Thus position and profile in my previous reply.
RE: Question about ISO_13920
Pmarc, so it is 10+/-0.5 because for parallelism?
Another question
In clause 4.3 it say , the following table 3 apply to both overall dimensions of a weldment, a welding assembly, or a welded structure, and also for sections for which dimensions are indicated.
i am a bit unsure who i shall interpret the term overall dimension
In a dictionary it says that overall means:
from one extreme limit of a thing to the other: the overall length of the bridge.
RE: Question about ISO_13920
If you want to meet the parallelism tolerance specified in Table 3, the absolute difference between measured distances shouldn't be greater than 1 (although one can rightly say this isn't 100% true).
As for "overall" dimension, yes, this is how I would interpret it. Something like total length, total height, etc. Is this what the authors of the standard had in mind? I have absolutely no idea.
Regardless of that, I think you already noticed how many problems hide behind use of standards that deal with the animal called "general tolerances". It actually does not matter whether we talk about welded (ISO 13920) or machined (ISO 2768) parts - these standards simply leave so much space for different interpretations that it is practically impossible to avoid ambiguity, even for such a simple part like yours.
One of the fundamental rules in dimensioning and tolerancing states that dimensions and tolerances shall not be subject to more than one interpretation. Thus, if one really cares about following this rule, she/he should stay away from general-tolerances standards as far as possible.
RE: Question about ISO_13920
About overall dimension. That would mean that 3 extra dimensions would be added on the drawing I posted on 22 Mar 14 12:30. But those dimensions would only indicate straightness flatness and parallelism?
For parallelism in ISO 13920, it states that it is valid for dimensions who are indicated. Indicated is a vague term (instead of a word like specified) and as CheckerHater stated ”o, 0 inch/mm, 0 degrees, 90 degrees and so on are usually implied and not specified on the drawing. ”. Was this how you derived your 10±0.5 tolerance pmarc?
RE: Question about ISO_13920
Perhaps it should not be understood that way, but this is not the main issue with the drawing you posted on 22 Mar 14 12:30. Even if you add 3 extra dimensions, this will not make this drawing unambiguous - at least in my opinion.