RE: UNTOLERANCED DIMENSIONS ARE BASIC note in drawing JNieman (Aerospace) 15 Apr 16 14:48 That'd be understandable in the pencil + paper days, but there's little excuse while drafting electronically. I'd bet CheckerHater is correct about the origin of the note: designers and drafters being lazy and not wanting to draw a box around many location dims.
![asme y14.5-2009 asme y14.5-2009](http://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1399426004i/8991548._UY630_SR1200,630_.jpg)
The question then is (as OP stated) which tolerance is valid? The UNTOLERANCED DIMENSIONS ARE BASIC note isn't very helpful, because a basic dim is untoleranced, not the other way around. The core of my own confusion about UNTOLERANCED DIMENSIONS ARE BASIC is what is an "untoleranced" dimension? If your drawing has a tolerance block, aren't all the dimensions toleranced by the block unless specifically noted otherwise? That's what's ambiguous to me the issue with the OP's drawing is something like the hole locations or whatever have TWO tolerances (one from the block applied to non-basic location dims and one from a positional callout), not zero. RE: UNTOLERANCED DIMENSIONS ARE BASIC note in drawing CheckerHater (Mechanical) 15 Apr 16 11:07 Very likely that is not what the designer is thinking, he is probably thinking a geometric control overrides a block tolerance always, but the use of the "UNTOLERANCED DIMENSIONS ARE BASIC" note on his drawing has allowed ambiguity into the interpretation of his drawing. And I say that only because that is how I understand the standard, which does allow, for instance, profile of a surface with an "ALL OVER" symbol to basically establish a worst-case variance of an entire part, to co-exist with refining tolerances that establish tolerance zones within the tolerance zone of the all-over control. I use tolerance block tolerances on dimensions for features of size only, and use explicit basic dimensions (dims with the basic box around them) for location dims or any other dimension that is toleranced without using the tolerance block.Īs far as interpreting the drawing you have, it's my understanding that the tighter tolerance wins. I still use a tolerance block on a drawing sheet, but removed the note. The thing is, the tolerance block is for the stated purpose of of providing tolerances to otherwise not-toleranced dimensions. We had this note on the block, and we also had a tolerance block.
![asme y14.5-2009 asme y14.5-2009](https://www.industrial-electronics.com/engineering-industrial/images/fund-tool-dsgn_13-2.jpg)
This note, in my interpretation, doesn't make any sense if you have a tolerance block that is giving a tolerance based on, say, number of decimal places shown.