Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
(OP)
Question on equalizing datums for you, with reference to the attached sketch (I've embedded the image too - it's only 95k so hopefully won't kill anyone's download time etc.) and ASME Y14.5M-1994 (I don't have 2009 and we still work to -1994).
As shown in the bottom left view, I want the major & minor axis to be used to generate datums B & C - essentially getting center planes from the length & width. The ellipse shape is the interface at the assembly level as it fits in an ellipse cut out.
If it was a machined part I'd do it as bottom left view labelled 'conventional datum structure'.
However, the part is to be cast and the foundry we work with usually prefers datum targets which is typical for castings. However, due to the shape of the part and it's functional interface I think Equalizing Datums using V type equalizers make sense rather than simple datum targets.
Q. I was hoping someone with some experience in these matters might be able to tell me if I've got it right in View A-A. Is it OK to use the V-type equalizers on both ends? Figure 4-38 only has them at one end with conventional targets at the other - though of course "The absence of a figure illustrating the desired application is neither reason to assume inapplicability, nor basis for drawing rejection".
Also before any one brings up my labeling of the center lines as datums in this case I believe it's acceptable per the last sentences of 4.6.6:
Thanks,Ken.
As shown in the bottom left view, I want the major & minor axis to be used to generate datums B & C - essentially getting center planes from the length & width. The ellipse shape is the interface at the assembly level as it fits in an ellipse cut out.
If it was a machined part I'd do it as bottom left view labelled 'conventional datum structure'.
However, the part is to be cast and the foundry we work with usually prefers datum targets which is typical for castings. However, due to the shape of the part and it's functional interface I think Equalizing Datums using V type equalizers make sense rather than simple datum targets.
Q. I was hoping someone with some experience in these matters might be able to tell me if I've got it right in View A-A. Is it OK to use the V-type equalizers on both ends? Figure 4-38 only has them at one end with conventional targets at the other - though of course "The absence of a figure illustrating the desired application is neither reason to assume inapplicability, nor basis for drawing rejection".
Also before any one brings up my labeling of the center lines as datums in this case I believe it's acceptable per the last sentences of 4.6.6:
Quote (ASME Y14.5M-1994 section 4.6.6 Equalizing Datums)
It is permissible, in such a case, to use the datum feature symbol to identify the equalized theoretical planes of the datum reference frame. It should be noted however, that its is an exception, and is to be done only when necessary and in conjunction with datum targets.
Thanks,Ken.
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RE: Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
RE: Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
I see no major issues with view A-A. Only some small remarks:
- I would try not to forget about adding profile of surface callout wrt A to the ellipse contour (just like it was done on bottom left view);
- The view A-A alone does not clarify whether V-type targets are planes or lines;
- Datums B and C labelling -- I do not think that it really matters, but to me somehow more logical would be to switch them, i.e. to make vertical plane B and horizontal C.
RE: Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
Interesting point on the flash/flaws. I'll discuss with the foundry but I don't think it will be an issue for this part depending where their riser is. I expect the mold split line will be along the C datum so any mismatch etc. will be away from where the V blocks touch.
On the right I was deliberately only showing the datum structure for clarity - yes I'd still need to dimension & tolerance the ellipse.
Per 4.6.6 "V-type planes may be indicated by only showing the lines in the top view" so if I don't show a height in another view they are assumed as planes correct?
Not that datum alphabetical order technically matters etc. but I was thinking the datum's made sense in the order I had them but I'm having trouble articulating my logic - care to expand on your thinking Pmarc?
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RE: Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
RE: Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
However, it occurs to me after your prompting that the parting line/mold half mismatch might be an issue.
In that case, could I make B or C my primary datum for later referencing, and change A to be a single datum point on the opposite side of the small ellipse (or similar) so as to allow face of what is currently datum A to be cleaned up by machining?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Question on Equalizing Datums ASME Y14.5M-1994 section 4.6.6
BTW, I actually do not know which datum target V-block is secondary and which tertiary. There is no feature control frame on the drawing specifying datum features order of precedence
BTW2, yes, if you do not show datum target lines in another view, the targets shown on A-A are assumed to be planes.