Datum in a second view 1

[vegabond]

The question I have is if a datum is identified in one view as the centerline of a "feature of size", how might I identify that centerline in another view? In the second view the centerline is the starting point for a half dimension and the datum feature is not visible.

Yes, I realize that GD&T would use possibly a profile callout or a TP callout instead of the half dimension. My problem is that I do not have the influence to mandate a chamge to GD&T. I would like to start by properly identifying datums. Currently, a datum symbol may be attached to a centerline that has 5 coincidental features and there is no way to know which feature truly is the datum.

I would put the conventional datum symbol in line with the FOS dimension line in the first view but what do you do in the second view?

Thanks in advance

 

[ringman]

Does your drawing state in accordance with A.S.M.E. Y14.5?

Are you familiar with Y14.5?

A datum identifier CANNOT BE APPLIED to a centerline. It must be associated with the FOS.

 

[vegabond]

No, it does not state ASME Y14.5
I am afraid that I used to be and now I am out of date with the current standard.

In the older revisions the datum "flag" could be attached to a centerline, identifying a centerline that may have been described by tooling points in another view. would this practice still be acceptable?

Thanks,
Vegabond

 

[ewh]

You can identify a centerline as a datum axis in another view. It is against the standard to identify a centerline as a datum without adding "axis" or "centerline" to the callout.

 

[vegabond]

Thanks for the reply, It is not clear to me what you mean by: Adding Axis or Centerline to the callout. If the datum symbol is in line with the "feature of size" dimension, ref FIG 3-4 pg 43 yi4.5, we already know that the Center is the datum in the first view. Are you talking about the callout in the second view?

 

[ewh]

Yes, I was refering to any subsequent callouts of that datum.

 

[ringman]

It would seem that to properly address your problem one would need to know the drawing standard being applied.

 

[Heckler]

Vegabond,

If the datum feature is a feature of size, the datum feature symbol is attached to or associated with the size dimension. By attaching or associating the datum feature symbol with a particular size dimension, it defines a specific point, axis or median plane that is derived from that feature as the datum.

Best Regards,

Heckler
Sr. Mechanical Engineer
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