Profile and Datum Question

[JLang17]

Please read:

thread1103-172988

Assuming the said cutout is sized with basic dimensions:

-Would you locate it, with basic dimensions, to the center of the cutout or to the edges of the cutout? (are both ways allowed?) I ask because it seems if it were located to center, then it could spin freely and need a datum reference to lock it in place. But if it's dimensioned to the edges, then you wouldn't need more datum references other than A? I guess I'm looking for clarity as to what referencing a full DRF would accomplish.

-Now my other question (which isn't related to the referenced thread, but possibly applicable). Can you locate a datum feature (with basic dimensions) from non-datum features? I feel like it's an obvious "Yes, you have to in many cases!" but I have yet to find something that covers this. Otherwise it seems you'd have to create a new Datum for the sole purpose of locating another Datum.

 

[JLang17]

ringster,

I understand that, I'm just coming up with some "what if" cases to help me understand the effects of referencing different datums.

 

[axym]

JLang17,

For the profile tolerance on the wall opposite C, all that is necessary is the reference to datum C. In this case, references to A or B would not constrain any meaningful degrees of freedom and should be omitted. I forgot to mention this in my previous post, but you've got it right.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[JLang17]

Thanks axym, that's what I thought.

 

[KENAT]

I thought I posted this before but couldn’t find it. If you really only care about parallelism to C, and it's geometry as simple as you make it sound so no tol stack issues, why not consider using a +- dim and a parallelism control rather than surface profile?

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484