Failed Derive Subtraction

[bcrowell]

I have an assembly (I cannot post it because it is proprietary) I derived into a part, put into an assembly to try and get the interior volume by subtracting it out.  I think I have closed at least most of the gaps, but there are parts clearly not subtracting. 

I'm not sure what it is that I'm doing wrong- all the parts in the assembly are selected to subtract, and even if the gaps weren't filled the parts should all subtract out and just leave connecting remnants between the solids.  I've posted pictures since I can't post the assembly.  You can see in the second picture that there is no cutout where the large stamped sheetmetal piece should be missing from the block.

[SBix26]

Can't tell what's wrong without the actual files, but another way to approach this is to derive the assembly into a part as surfaces, then sculpt the interior from the enclosing surfaces plus others you create to close off any gaps.

[bcrowell]

So far I haven't had any luck with the Sculpting.  I have sealed all gaps as far as I can tell.  I think what may be freaking it out is that there are interior surfaces, too, which may not allow it to subtract in the direction- as of yet it looks promising but not yet attained.