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repeat datums multi sheet drawings

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dakeb

dakeb

Mechanical
Dec 1, 2004
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Guys,

On a multi-sheet drawing of a comlex machined part I want to specify some of the datums on more than one sheet so that the manufacturer is not continually flicking thru sheets looking for them.

I am not sure if that is regarded as dual-dimensioning, I cannot find anything in ISO 5459 or 1101 about it. For a datum, is it allowed to repeat the declaration? Or should I declare it once, and then on subsequent sheets write 'ref' after the datum symbol?

How do others do this, and which standard governs that practise?

Thanks

Dave
 
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dakeb,

I am not sure how ISO standards deal with this but in ASME Y14.5-2009 standard in section 3.3.2 (page 38) you can find following note:

"Where the same datum feature symbol is repeated to identify the same feature in other locations of a drawing, it needs to be identified as reference."

I think this can also apply to a multi-sheet drawings case.
 
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It appears that ASME Y14.5-2009 and ASME Y14.5-1994 differ in this regard. From pg. 41 Section 3.3.2 it states:

"Where the same datum feature symbol is repeated to identify the same feature in other locations of a drawing, it need not be identified as reference."
 
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As the others (finally;-)) agreed on, to ASME stds the datums can be repeated, without having to indicate ref etc.

We also used to do this in the UK to ISO based standards though I can't claim to remember a reference to justify it.

Posting guidelines faq731-376 (probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​
 
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I agree with the others, and am only posting to offer KENAT the congrats he deserves!!!

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
 
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How do you show a basic dimension on a view that does not have the datum feature shown. Do you draw in a center line in space and attach a basic dimension to it? How do you handle this?

Do you follow the new 2009 convention X[A,B,C]? We have not adapted this yet as it will clutter the drawing some fierce.

Adding a datum with (ref) seems to me make the most sense as you are not defining that the feature in that view only saying "Hey this dimension starts from datum x". This is clearly against the standard however, bummer...
 
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You don't have to define the feature to reference the datum... it is what is is and you are saying "Hey, this is Datum X."

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
 
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As long as you can chain basic dimensions back to the datum, you don't need a basic dimension for each feature directly back to the datum. If, on the other hand, you do want to dimension to a centerline which is the representation of the datum axis, then you can indeed dimension to it. Either way, it's the same outcome because "Basic + Basic = Basic"; i.e. no accumulation of errors.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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