Concrete Sphere Mold

thingiverse

This is a concrete mold that creates a 6" sphere. The filament is PLA. There is a groove and lip that snaps together when filling it. To use it, spray the inside with a cooking spray like Pam. It will help keep the concrete from sticking to the mold. I sprayed the bowl and wiped it with a paper towel to spread it around. It doesn't need to be dripping with release. Include the lip where they meet together to aid in clean up. Fill the bottom half with concrete and tap the outside lightly to release air bubbles. Then press the top on and clamp it with large binder clips. Then continue filling with concrete, tapping as you go. I filled just shy of the port hole, which will create a flat spot when released. I used Quikrete Countertop mix as the aggregate is small. When it's full, let it sit for about 1 day to harden up. Then take a box cutter or thin knife and slip it between the two halves and pry gently at various points around the mold. The top should release. Turn it upside down and flex the bottom lip a bit. You may have to score around the area where the ball meets the lip with a box cutter to aid in releasing it but it should come out. You can clean up lines with sand paper or a diamond sanding pad designed for concrete. If you've coated it with Pam, it should easily clean up for the next use. Some people expressed concern that the concrete would heat up and ruin the mold but the amount of concrete required is pretty small and any temperature rise is negligible (it still felt cool to the touch).