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Datums call out @ part center is correct?
4

Datums call out @ part center is correct?

Datums call out @ part center is correct?

(OP)
Please see attached image. Can i use part center to call out datums?
Please help me to understand, why i can use it.

Thanks,
Darsh

RE: Datums call out @ part center is correct?

Quote (darshan84)

Can i use part center to call out datums?

Yes you can have a datum derived from some defined feature (such as part overall dimension) which is effectively the center plane of that feature.

thread1103-292841: Centerlines as Datums and plenty of others http://www.eng-tips.com/search.cfm?pid=1103&ac... touch on this.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Datums call out @ part center is correct?

(OP)
I am refering to Datum B in attached image.

RE: Datums call out @ part center is correct?

Darshan84,

No, you can't use a part centerline to define a datum as shown in your examples. The datum feature symbol must be associated with a particular feature, or features.

Evan Janeshewski

Axymetrix Quality Engineering Inc.
www.axymetrix.ca

RE: Datums call out @ part center is correct?

As stated above, you can't have a datum symbol attached to a non-touchable center. There are a couple of reasons, but the main one is that we don't know exactly what center is being referred to: Is it the center plane derived from the outside width? Inside width? Middle plane of the holes' location? And so on.

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

RE: Datums call out @ part center is correct?

Darshan84

You sure will ask why I can't use the center line as a datum feature, here is the answer for you. Even ISO GPS not allow the datum symbol place on the center line on the new standard.
http://www.youtube.com/watch?v=xbA4FrZnZVM

From the point of view on datum point (0.0,0.0) on your last post, use the hole pattern as a datum feature is a good practice as mentioned by Paul.

Season

RE: Datums call out @ part center is correct?

(OP)
Thanks all....for your kindly suggestion...

RE: Datums call out @ part center is correct?

Just a point of interest. Your callout for Datum C is also wrong for the reasons stated above.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

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