Sem_D220
Mechanical
- Jul 9, 2018
- 290
As requested by pmarc, I'd like to continue here the discussion about CDRF concept, which started to take over thread1103-441690 , in order to allow it to get back to it's initial topic. For those who were not involved but hopefully also interested - we were discussing the difference between a Translation Modifier and Customized Datum Reference Frame. It was pointed out by pmarc and agreed that CDRF is only intended to override the degrees of freedom constrained by each datum feature according to datum precedence order for a given DRF, and unlike in case of a Translation Modifier, the general requirement for basic location of datum feature simulators relative to each other (para 4.5.2 (c) at Y14.5), is in force in the case of CDRF. In the standard there is also sub-paragraph 4.5.2 (b), which requires basic orientation of datum feature simulators to each other, and doesn't exclude any cases.
pmarc, if I understand your last post on this topic in the mentioned thread regarding this example correctly, you agree that mobility of datum feature C is not allowed for both customized and non-customized DRFs, but you don't find the relative rotation between datum feature simulators B and C in the Customized DRF problematic. You mentioned that para. 4.5.2 is not well written and fails to describe all permitted behaviors of datum feature simulators (figs. 4-30(a) and4-31(b) 4-31(a) brought up as examples). Can it be concluded that someone "forgot" to exclude the Customized Datum Reference Frame from the requirement at 4.5.2 (b)?
Then how do we know for sure that 4.5.2 (c) is in force for CDRF? Perhaps it was intended to exclude it for basic location too? Is there some kind of common convention that datum feature simulators can be of adjustable orientation to each other in a CDRF, but fixed at relative location?
As for the other issue we discussed - thank you very much for explaining how the datum feature simulator fig 4-30(a) should behave in case of a direct tolerance dimension and no profile tolerance. It was very helpful for me.
semiond
pmarc, if I understand your last post on this topic in the mentioned thread regarding this example correctly, you agree that mobility of datum feature C is not allowed for both customized and non-customized DRFs, but you don't find the relative rotation between datum feature simulators B and C in the Customized DRF problematic. You mentioned that para. 4.5.2 is not well written and fails to describe all permitted behaviors of datum feature simulators (figs. 4-30(a) and
Then how do we know for sure that 4.5.2 (c) is in force for CDRF? Perhaps it was intended to exclude it for basic location too? Is there some kind of common convention that datum feature simulators can be of adjustable orientation to each other in a CDRF, but fixed at relative location?
As for the other issue we discussed - thank you very much for explaining how the datum feature simulator fig 4-30(a) should behave in case of a direct tolerance dimension and no profile tolerance. It was very helpful for me.
semiond
