huangyhg

title block tollerance vs. notes
hey guys,
i just had a print brought to my attention that has a standard drawing title block tolerance and then a repeat, fine-tune of that tollerance in the notes (see attached file).
we observe asme y14.5m.
this approach doesn't sit right, however, i'm wondering if you guys know of some "fine print" that suggests that finer tollerances supersede drawing block tollerances??
thanks for your input,
jack
i would use the tighter tolerances to play it safe, because that is an ambiguous drawing. the notes state "unless otherwise noted" which can be interpreted to include the title block tolerances, thus the ambiguity.
when the people fear their government, there is tyranny; when the government fears the people, there is liberty.fff"> - thomas jefferson

the first line in every general note that i have seen, including the example, has stated: "unless otherwise specified." i was always taught that general notes superseded everything on the drawing, including general tolerances in the title block. i can't find a hard standard that states this though... i would also follow the tols in the notes.

"art without engineering is dreaming; engineering without art is calculating."
i would leave the tolerances off of the notes and use the tol block. if there are any variations of the tol block, indicate them within the dimensions themselves.
"unless otherwise specified" should be indicated notes that may vary from the rest of the dwg.
chris
solidworks/pdmworks 08 3.1
autocad 08
well it's been discussed on here before that block tolerances where the tolerance varies with the amount of decimal places doesn't work well with asme y14.5m-1994 since section 1.6 says not to have trailing 0's on metric dimensions. you can have a note on the drawing or in your company standard stating that you don't comply with this part of the standard but i don't see it listed on your sample drawing.
so despite what the title block says this drawing doesn't appear to explicitly comply with 14.5. block tolerances are dealt with in y14.1 which i don't sadly have a copy of to hand.
there is an argument that the block tolerances should never get changed because people get used to them and switching them causes confusion. in this case it may be appropriate to have a different 'block tolerance' in the notes, howeverfff"> it would have to be made clear in the notes that this 'block tolerance' supplants the tolerance actually in the title block. this is not done on the drawing you posted. as such the drawing you post is, to me, unclear.
in summary, i believe it could be made to work but your sample doesn't explicitly do so.

kenat,
to clarify the drawing intent (if the note tolerances were intended to be used), the block tolerances should be crossed out.
when the people fear their government, there is tyranny; when the government fears the people, there is liberty.fff"> - thomas jefferson

i agree whole heartedly with ewh. i expect the intent is to use the tolerances in the notes. two things lead me to this. the tolerances are tighter and the notes are all dual language while the title block is not. still, very bad practice.
further on kenat's comment about suppressing trailing zero's on metric drawings & default tolerances, we have always only had one default linear tolerance in our title blocks, regardless of decimal places. it seems to be a much more foolproof system, particularly since we have been forced to have some imperial unit drawings in recent years, much to my disgust.
ewh, crossing out the title block tolerances is better than my idea of a clarifying note, nice.
also, when i say the "block tolerances where the tolerance varies with the amount of decimal places doesn't work well with asme y14.5m-1994 " i want to make it clear it was for metric, not inch. it can work well for inch if people actually pay attention to what tolerance they are specifying.
kenat,
possible other issues with the part?:
-break sharp edges bigger than the thickness of the material?
-does this material come in this thickness?
-possible problems with anodize after bending tab?
-i agree about the trailing zeros. some of these dimensions are hard to tell if ".3" or "3".
chris
solidworks/pdmworks 08 3.1
autocad 08
at the company i work the title block tolerances are never changed and if we have dimensions that need to be controlled differently (tighter or looser) we place the tolerance on the dimension. i have done many drawings where most of the dimensions have a tolerance placed on them and there are only a couple of dimensions that use the title block tolerances. that way there shouldn't be any confusion.
but i agree with evoldiesel that the method on this drawing leaves too much open for interpretation.
i created a title block tol section that states "unless otherwise specified in other portions of this drawing" to mean that even if another portion of the drawing says "unless otherwise specified" it will still supersede the title block tol section. it establishes a hierarchy of specifications. if nothing else is stated, then apply the title block tols. if the general notes also state tols, then those supersede the title block tols. if a local note or dim specified a tol, then that supersedes the general notes and the title block notes.
in the case of your drawing, the vendor could claim the drawing means that the looser tols are specified. unless you have it defined somewhere, somehow, the court will likely side with the vendor if this went to trial in a lawsuit.

matt lorono
cad engineer/ecn analyst
silicon valley, ca

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