profile on trimmed edge 8

[DGN1975]

does anyone have idea or references how to profile tolerance a complex trimmed edge on say a vac formed part? I don't really see any good examples in the standard to other places. Would it make sense to just point to the trimmed edge with a 'ALL OVER' profile tolerance with a note below that states "trimmed edge". using "all around" wouldn't work to me as it is controlled only in the view its shown in and a trimmed edge would go all around in 3d.

 

[3DDave]

I have encountered all of the types of datums listed, except "line". Didn't find an example in the standard either. Perhaps someone on this forum can help - what is a datum line? What is the corresponding datum feature and datum feature simulator from which it is derived?

Interesting to note: according to the quote you provided, "line" wasn't included in the 1994 or earlier versions. I wonder what it was added for, especially since no examples were provided.

I hope it is not too late to ask - does anybody else share my conclusion or can confirm that the "line" mentioned in the definition of the datum concept is the "line in plane" as presented in this figure?
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It wasn't clear what a Y14.5 datum line was then; nothing in the standard changed since. Who am I to argue the obvious conclusion that it wasn't described in Y14.5 by a faithful student - lack of definition is a problem that was not resolved. No one confirmed.

https://www.eng-tips.com/viewthread.cfm?qid=452649

Mind that there is extensive theoretical research on datum lines, but the standard writers failed to include it.

The most likely source for Y14.5 is copy/paste from ISO, which does support datum lines.

In ISO 5459, the datum related definitions and datum establishing methods are as follows:

Datum:
A theoretically exact geometric reference (such as axes, planes, straight lines, etc.) to which
toleranced feature are related. Datums may be based on one or more datum features of a part.

Once a line is OK for a datum one can toleracnce it too, even if the definitions are from another standard:

Position tolerance of a line:
The tolerance is limited by one of the three types of tolerance zones:
- two parallel straight lines (in two dimensions) a distance t apart disposed
symmetrically with respect to the theoretically exact position,
- a parallelpiped of sections of t x t , the axis of which is in the theoretically exact 1 2
position,
- a cylinder of diameter of t, the axis of which is in the theoretically exact position,
within one of these tolerance zones the axis of a feature or a line must lie.

So obvious. ISO also allows position to be used to control planar face locations.

 

[randy64]

Is this bickering really necessary?

I assume they're both retired/unemployed, 'cause they sure as heck don't have much time to get work done...

 

[3DDave]

ISO uses lines. Y14.5 does not. You can find examples in ISO - they are not haphazard as Y14.5 is.

"4.1 Datum being a straight line or a plane" per ISO 5459-1981.

The 2011 version is even more extensive.

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"what is a datum line?" contradicts "If there was no definition, the question I asked more than 4 years ago wouldn't have been asked in the first place." because, if there was a definition, you would not have asked.

What was defined was "datum," the general term, not datum line. There is a defective definition for datum, there is no definition for datum line.

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ewh - I attack the defects in the standard, Burunduk bickers about it. Also, if you have clear evidence of how datum lines were introduced and what for, noting it wasn't a noted change in 2009, chime in. It looks like harmonization for the sake of harmonization as was the drawing trash toilet plunger change and not actually adding the basis work.

 

[3DDave]

Borrowing rules from unrelated standards does not support your conclusion. The clear contrast makes obvious the lacking in Y14.5.

Why so defensive of so flawed a product?

 

[ewh]

3D,
My comment was more about the back and forth over a subject not addressed by the OP. If you must divine the secret of datum line vs axis, create a new thread, as the standard does have its weaknesses.
Your current discussion has little to do with the original thread other than they both involve Y14.5. It reminds me of an old married couple who can only communicate by bickering.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV