Buy 4x4x6s here- http://tonyfisherpuzzles.net/PuzzleShopCuboids.html This is a fully functional 4x4x6 transformation of a 4x4x4 Master Cube / Rubik's Revenge. It was inspired by Geert Helling's ingenious idea of adding two new working layers to a 4x4x4. He went on to make a fully functional 2x2x6 though with non cubic cubies. I expanded on this idea to make a fully functional correctly proportioned 2x2x6 cuboid . In 2004 I took this idea even further to create a fully functional correctly proportion 4x4x6 cuboid. Most of my transformations do not affect the mechanisms but this puzzle needs additional functionality. Without the use of rapid prototyping that is far from easy. The extra pieces were made from polyester resin and metal for the narrow parts of the new corners. For stickers I used basic Rubik's Cube style which were actually taken from spare Master Cubes. When I made the first video I did not show the puzzle changing shape since it becomes very loose and unstable. However several people asked for proof that it is capable of shape changing so I added a new video. It can change shape since it obeys the cuboid shape changing rule- "A cuboid is capable of shape changing when ( two or more edge unit lengths are different and odd ) or ( two or more edge unit lengths are different and even ) excluding cuboids with a side of one." In total I have made eleven fully functional cuboids. They are- 2x2x3 (micro), 2x2x4, 2x2x6, 2x2x7, 2x3x4, 3x3x4 (large), 3x3x4 (medium), 3x3x5, 3x4x4, 4x4x5, 4x4x6, 5x5x6.
See- http://tonyfisherpuzzles.net for photos and more information on this and all my other puzzles.