Repeat Datums in a drawing 1

[rbreyette]

Hello,

I have a question regarding repeat datum's in a drawing and if ASME talks about the rules to follow. At my company we have multiple parts on a drawing (some that don't even have anything to do with each other). We sometimes use the same datum on different parts. I was told by our senior drafter (45yrs experience) that ASME says that you should not use the same datum twice on a document/drawing. We try to follow this rule but sometime it so happens we have datum A on one sheet and datum A on another sheet, but they are different parts. Can anyone point me to the ASME standard that talks about not using the same datum twice on a drawing? If this is even a rule? It kinda makes sense to me but need the info to back it up.

I am used to a part/assembly having its own drawing. But at my current company they put a number assemblies and parts in the same drawing.

Thanks for your help.
Ryan

 

[Belanger]

One thing in Y14.5 might be paragraph 3.3.2 (near the end of the first paragraph in there). But that is talking about the same datum letter for the same feature, just in different views.

For what you're asking about, maybe peruse all the subparagraphs in paragraph 1.4. But I think simple common sense would say that you want to prevent any chance for there to be confusion on a print.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[CheckerHater]

No, I am quite sure ASME doesn't say anything about datum features on multidetail drawings.
In fact, both 1989 and 2012 version of ASME Y14.24 are carefully steering away from the issue.

But it's always helpful (and fun) to ask an "expert" to produce actual standard. "Just show me where it says so"
On the other hand, as accepted practice, it is not without merit. In fact some local standard recommend not to mix same letters in datums and views designations.
ASME will have no problem with View A, Section A-A, and Datum A on the same sheet.

So use your best judgement - make your drawings the way that no one will come back to ask you questions.
Good luck

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[dgallup]

Personally, I'm completely against having multiple parts on a drawing. Since the drawing can only have one drawing number, how do you find the drawing for the other parts? We had a draftsperson that did that back in the very early days of CAD. He was let go.

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[CheckerHater]

I have to correct myself, as the standard has vague, but requirement nevertheless:

3.2.3 Requirements. Each part delineation on a multidetail drawing meets the design definition requirements for a monodetail drawing and shall be uniquely identified.

The latest edition still mention multi-detail drawing, but edited requirement to make it even more fuzzy:

5.2.3 Requirements. Each part delineation on a multi-detail drawing shall meet the design definition requirements for a monodetail drawing. Each part shall be separately identified.

And to play devil's advocate for a while, part number and drawing number are two different things. (I totally agree that advances in CAD made creation of separate drawing sheets for everything easy - maybe too easy)

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[drawoh]

Personally, I'm completely against having multiple parts on a drawing.

Tabulate the drawing.

I have done multiple part drawings way back in the very distant past. The process worked fine on one-off plant equipment designed on an E-sized sheet on a drafting board. I don't see why I would do this on SolidWorks.

--
JHG

 

[dgallup]

I'm all for tabulating drawings of similar parts with only a few differing dimensions or features but the OP said: "At my company we have multiple parts on a drawing (some that don't even have anything to do with each other)." That is just a no-no to me.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[ctopher]

Multiple parts on a drawing of same part number with dash numbers are fine, but not different part numbers. This causes confusion for other departments.
Sharing datum's is also confusing for inspection. Keep it clear for everyone and use new datum's.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

 

[3DDave]

If an inspector is confused about which views and datums apply to an item they are inspecting they need to reconsider their career choice.

My (unfavorite) multiple parts on one drawing: NASM MS124771 THRU MS124810. Because someone thought dash numbers were evil or something.

 

[ctopher]

By sharing I mean having a sheet with views using datum A, then the same sheet (or another sheet) with views with datum A.
Technically, the shared datum A can be crossed and confuse the machinist and inspector.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

 

[tbuelna]

The 14.5 standard explains the protocol for assigning datum ID's, and there is no limit to the number of ID's available. Every engineering document should be as explicit as possible in its definition of a product, and leave no room for interpretation. So why duplicate datum ID's on a multi-detail drawing when there is no need to?