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Reusing the same datum symbol for differnt parts on the same sheet

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Diametrix

Diametrix

Aerospace
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I ran across this drawing where there were several views for two cylindrical parts and their assembly combined on a single sheet. The parts get pressed inside of each other and then a single hole is drilled through the assembly. What caught my attention was that each view was reusing the same letter for the datum symbol. Aside from the fact wither it is a good practice, does it violate anything in the standard to reuse the same letter?

Datum_Symbol_pexvzs.jpg
 
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That's poor drafting practice, very common these days.

ASTM Y14.5-2018
6.3.2, Each datum feature shall be assigned a different letter.

Chris, CSWP
SolidWorks
ctophers home
 
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From 6.3.2: "Each datum feature of a part requiring identification shall be assigned a different letter." [emphasis mine]

I agree it is sloppy drafting, but the devil is in the details. The drawing is referring to two different parts used to create a third. the datums are being applied to different parts so are allowed for those parts.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
 
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Yeah, that's the only reference I found too. The question I have is about the assembly view. Is that considered to be a "part" as well or is it simply "repeating" the datum from the part view. If it is the former, then the datum A in the assembly view is a unique datum and there are no issues aside from it being confusing. If the latter, then you can technically "repeat" the other datum as well and have two datums A on different features of the assembly.
 
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Hi, Diametrix:

The assembly view is the third item. Datum A on this item is different from Datum A on item #2.

I think ASME Y14 committee intended to state it as follows:

"Each datum feature of parts and assemblies on a print requiring identification shall be assigned a different letter."

Best regards,

Alex
 
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To minimize confusion, datum's should not be reused on a dwg. If you question it, so will a machinist/inspector/etc.

Chris, CSWP
SolidWorks
ctophers home
 
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ctopher said:
To minimize confusion, datum's should not be reused on a dwg. If you question it, so will a machinist/inspector/etc
Click to expand...
No argument from me. I was just trying to see if there is something in the standards to substantiate it.
 
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Y14.5-2009 "Each datum feature of a part requiring identification shall be assigned a different letter"
Y14.5-2018 "Each datum feature of a part requiring identification shall be assigned a different letter"

Section and view identifiers should not be repeated. Unlike datum features, those are part of the drawing.

Which standard contains "Each datum feature of parts and assemblies on a print requiring identification shall be assigned a different letter."?

Poor practice or not it cannot be that a datum feature on one part has any influence on another part. It's worthwhile as a "Can you read a drawing?" test and ask why a feature of one part is thought to influence any other part.
 
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Well, it does not matter what the standard says. It is a terrible idea to have the same datum label pointing to different objects (part/assembly) and features.

Best regards,

Alex
 
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Hi, Diametrix:

This is an uncharted area. According to ASME Y14.24-2012, the print you posted is a combination of different drawing types. ASME Y14.24 dis-encourages use of combination of drawing types. Please take a look at section 1.8 from ASME Y14.24-2012.

1.8 Combination of Drawing Types
The characteristics of more than one drawing type
may be combined into a single drawing provided the
resulting combination includes the data required by each
of the individual types. For example, a modification kit
drawing combines a description of the modification and
the kit of items needed to accomplish the modification.
NOTE: The decision to combine drawings should be made cautiously.
Combining drawing types should result in a significant
advantage versus not combining and having separate drawings.
Advantages of combining drawings should outweigh any potential
disadvantages. Potential disadvantages resulting from combining
drawings include
(a) increased complexity of the drawing, which may diminish
clarity and usefulness
(b) frequent change activity to the drawing, which may increase
the need to update associated record(s), material control data,
manufacturing planning, microfilm, etc.
 
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