I recently finished the prototype for my third puzzle, The Core Cube. I played around with a couple of variations of this puzzle in SketchUp, and finally settled on the diagonal open feature on the sides of the cube with the "core cube" caged in the center. The puzzle consists of thirteen pieces that assemble into a 3"x3"x3" cube. I typically use red oak in many of my fine woodworking projects, but for this prototype I opted for inexpensive poplar. In hindsight, I should have just used red oak or mahogany; poplar is soft like white pine and prone to tear-out. I replaced the blade on my saw and used a zero-clearance jig I built to minimize this, but some defects are still evident on the small workpieces. I suppose that's why they're called prototypes. For future productions of this puzzle, I will be ripping down my own stock from mahogany, one of my favorite woods.