There are many ways, but without knowing what your model looks like as well as the version of NX you're using is going to make it difficult to offer anything other than guesses.
Tim Flater
NX Designer
NX 8.0.3.4
Win7 Pro x64 SP1
Intel Xeon 2.53 GHz 6GB RAM
NVIDIA Quadro 4000 2GB
- Change the Operation Navigator to the Geometry view.
- Edit the WORKPIECE.
- Pick 'Specify Blank'
- Expand the Type drop down list at the top of the dialog to see the options.
- Select Bounding Block or what ever shape or selection suits your need.
Then just make sure your operations are children of this WORKPIECE parent so they inherit the blank definition.
If there is a better way maybe somebody else will post it?