I used some spray adhesive I already had on hand to hold the foam sheets together while I cut them out. This adhesive didn't form a strong bond, I planned to use Gorilla Glue (polyeurethane) but I thought this glue layer might be hard to cut through.

I first traced the paper patterns with a sharpie. Then slowly cut out each 2" thick shape. The video above has been sped up ten times.

With all the pieces cut out I separated them and cleaned the adhesive off with some rubbing alcohol. I then spread a thin layer (as thin as I possibly could) of Gorilla Glue between the halves and clamped them together to set.

Wrenches (this has been curing for 2-3 hours)

The skull during curing.