1.4 - fundamental rule (o)

[AndrewTT]

(o) - Dimensions and Tolerances apply only at the drawing level where they are specified. A dimension specified for a given feature on one level of drawing is not mandatory for that feature at any other level.

Example: I have a machined casting that has many as-cast surfaces remaining on it. These as-cast surfaces are important for proper part function. Based upon fundamental rule (o) I need to put these casting dimensions on the machined part drawing or they can be modified during machining and the machined part is acceptable even though the important as-cast surfaces have been detrimentally changed. That is how I read fundamental rule (o).

How do people handle this situation? Do you actually put all remaining as-cast surface dimensions on the machined part print (in duplication of what is already on the casting drawing), making the machined part drawing extremely complicated to read? Or, do you put a note stating that as-cast surfaces are not to be modified from the casting print during machining?

Thank you.

 

[pmarc]

3DDave,
Like I said, a lot depends on circumstances. If for company A buying off-the-shelf machined cast item works fine, so be it. But if for company B, for different reasons, it is indispensable to have separate cast item drawing, sticking to the "drawing should define the end item" paradigm is not necessarily the best solution, as I tried to explain.

 

[3DDave]

pmarc,

What I was getting at was that companies that determine the drawing must be separate when they make the parts don't also find the need when buying equivalent parts. And that the reason they don't do that is purchasing convenience or processing on the drawing, neither of which helps the acceptance of the parts in their final configuration because of the disconnect between the two stages, a disconnect they avoid when buying off the shelf with a single drawing, but is self-inflicted otherwise.

Recall that this thread was about what to do about machining drawing needs to control/depend on an otherwise cast feature.

Any discussion that devolves to 'it depends on circumstances' has already lost most of the wind from its sails. Everything depends on circumstances. Saying so doesn't advance a course of action or a means of deciding which action to take.

You have passed the point of explaining into trying to convince. As I've already explained both sides of the problem there isn't any convincing necessary. If someone pays me to do something one way or the other I really don't care, but if someone wants the best final part then I have a reason to not divide the description of the part among several drawings.

The only convincing I'd like to do is to move people off the idea that a dimension can only apply at one point in the drawing structure because it might detect a flaw in the manufacturing process - and the standard allows that to happen.

 

[pmarc]

3DDave,

I was not trying to convince you - I merely wanted to point out that there are valid reasons to use both methods depending on circumstances different specific factors. Single-drawing approach caused my company a lot of troubles in the past (in addition to what I already said about impossibility to have everything specified on a single drawing due to key technology control), and that is why the decision was made to have separate drawings. You described your bad experience with separate-drawings approach and I see your point. But that does not mean one approach is always better than the other.