When the Ultimaker 2 finishes its prints the build bed drops to the bottom automatically. To avoid any injury to cats that may be investigating at the time I have added this simple clear door to cover the front hole.The print is just the hook.  It needs to be screwed to an acrylic sheet.The nuts are encapsulated in hexagonal holes in the design, to make it easy to assemble. ==2015-07-27: I have uploaded a new STL file to the correct scale!