This may be of interest to those with an interest in metal casting, it's a useful idea but not something I've seen mentioned in books on the subject.
I made this a few years ago, it's a core box for a toothed wheel with slightly under undercut teeth which made a normal pattern unworkable. Unfortunately I don't have a photo of the finished casting but it was quite successful and cast in manganese bronze .
The central plug is removable and tapered and the blue silicon is indexed to the plug. I use sodium silicate bonded sand as a core material and it serves well .The sand is packed in the mold, gassed with CO2 then the central plug is removed then the blue silicon is peeled out . The bottom photo shows the finished core .