I have modeled a part but it consists of the original solid core and a geometric shaped surface which I made (took me more hours than I would care to admit).

My questions is, how would I make the cavity between the solid core and the geometric surface completly solid? I dont suppose there is a button that will auto fill cavities!!!

If it helps I can attach the part files.

Thanks in advance

EDIT: EDIT: I tried pack and go with the main assembly but that was unsuccessful, So I have now tried adding just the single part file that is relevant. Sorry for the faff.