Hey sneather,
"""""""""""Do you know whether there is a separate units option in the STEP export process from NX?
Again, I trust the designer when he says that they work in inches, inside NX. So maybe it's an export-related issue?""""""""""

I dont think so, but NX is a higher end modeler and has several different ways it handles units. The only real way to track it down would be to get the nx file to someone like Danny, who could then review it's particular setup. There should be no problen with working directly from NX to MoI.

I would be certain the model looks good in NX. NX using the parasolids kernel, will have several different means to construct geometry in "difficult" areas. Like the area where you are showing a problem, looks like one of those areas where the filleter crashes into and goes beyond itself (this would fail with MoI's filleter), but generates a result. The translation of that area just isnt going through the 2 translators, nx's export and moi's import, as intended.

My suggestion would be to ask the designer to provide you with a few of the formats that MoI handles when sending the models over. Package up a STEP, IGES and a SAT. Then, you can find the one that imports the parts as intended. You will find that different models (areas of difficult surface generation) will come through in different formats. Try an iges, the most generic surface translator.