Setting Up Single Datum Reference for Positional Characteristics

[[Do...]]

I have a bracket where I have a positional callout going back to a single datum and am curious as to what the standard practice is for setting this up. Is it something as simple as selecting the hole for the characteristic and then only selecting the opposing single datum hole under the "datum" section. Or is there some sort of specialized alignment that needs to be setup first and then referenced within the characteristic side? Our engineering group has relayed that the intent is to control the hole to the single datum hole only due to the variation that is inherent within the bending process during manufacture of the bracket.

[[Ma...]]

Unfortunately this is wrong selection of datums.

At least one more datum should be required - i would prefer plane where is datum D. Alternatively a perpendicular plane to that plane.

From this sheet you can not have strong datum to such small tolerance over that big distance.
It should be better to ask engineer which of those planes are available to be a datum.

Edited yesterday at 09:47 PM

[[Do...]]

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 our engineers said that the plane that datum D lies on can be used. Does this help?

[[Ma...]]

Yes, then let's name that plane as datum E - so you would have |TP|Ø.028|E|D|

So now evaluated hole would have to be in center of datum D, but direction will be taken from datum E. Now it will cover possibility of a mismatched hole during bending the sheet.

[[Ke...]]

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Can that plane be used? Definitely... is it the best plane to use? Probably not. With stamped/bending parts, there may be variability in the angle of that plane, that will affect the the results. Consider when these parts are run during general production: Presuming that these are stamped parts, using a progressive die - There will likely be slight changes in material thickness from coil to coil. That slight change will likely  result in changes in the angle of that plane. If the angle of that plane can be tightly controlled, then it may not be an issue; but it sounds like this is not the case

What are your primary Datums for the part?

Edited 10 hours ago

[[Ze...]]

Knowing nothing about the functionality of the part I would argue that both holes should be Datum D and whatever GD&T is controlling the one hole should control both simultaneously, especially if the intent is that both holes should be in line with each other for assembly. 

[[Ra...]]

To accomplish this to the original print, you would need to evaluate datum feature D as a cylinder, which I doubt is possible based on the image. Is the hole in question concentric to datum D?

 

I personally would want, at the minimum, a corrected "Red-Line" drawing showing exactly what datums to use. Either from your engineers or the customer. It's a scary world when your inspection program gets audited and it's easy to prove it wasn't designed with the print intent. Much more so when you have zero documents to support you. 

[[Do...]]

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Back face is datum A, large center hole is datum B, and the lower right smaller diameter hole is datum C.

[[Ke...]]

I presumed something similar to that... AIBIC obviously fully constrains the part. 

I also presume that what the engineer wants to use as Datum D is being evaluated to AIBIC?

I would suggest making a notation on the print that the two holes are to be considered a single feature. This way, you can evaluate the two holes together as a Cylinder; so that if either hole is out of position then the part "fails"

The only other way that I can think of that would make sense for this type of part, would be to constrain Datum D to AIBIC (this way AIBIC controls orientation, and Datum D would define the nominal position)... I am unsure of how this would need to be noted/called out to make it "legal"

Edited 6 hours ago

[[Do...]]

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Yes, the hole in question is to be in-line (concentric) with the datum D hole.

[[Ch...]]

ASME Y14.5 mentions datums should be of 'sufficient size', I would say Datum D single hole is insufficient size for a 'primary' 'leveling datum'.

I would suggest using the outer face of D as a REF plane and measuring D as a circle, and position to those...only as a REF check, etc.