datum targets

[dho]

we have a forging. one of the datum points is right on the raised marking (part number) letter. where in Y14.5 saying the datum point should be moved/adjusted?
thanks.

 

[HGMorgan]

Can we see the drawing? Sometimes, especially on a forging, a Datum Target is called out with a circle, horizontal line thru middle, a Dia value above line, and Datum id below line. The Dia value is the circular zone the Datum point must be in, but it can be anywhere in that zone. Also, if DT leader is dashed, the target is on the hidden part surface of that view.

Harold G. Morgan
CATIA, QA, CNC & CMM Programmer

 

[drawoh]

dho,

Another trick used on castings is to cast in raised points to be used as datum targets. Maybe they are multi-purposing their part number.

--
JHG

 

[pmarc]

I think you should rather search in Y14.8 "Castings, Forgings, and Molded Parts" (the newest version is from 2009).
After doing a quick search I was just able to find following statement in para. 4.3.1:
"Datum targets should be located as follows:
[...]
(c) on features not subject to processing variables, such as parting lines, flash extensions, etc.[...]"

If on the drawing you are dealing with the height of marking is not decently controlled (because for instance it is not critical from functional point of view), I think this falls under the 4.3.1(c).

 

[Tunalover]

@pmarc- I'm with you. More people should turn to the Y14.8 standard first when a question comes up about dimensioning and tolerancing of forgings, castings, and injection moldings.



Tunalover

 

[KENAT]

Another vote for 14.8. I don't have a copy to hand but I think it may even make mention of this type of thing in there.

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