I decided to forgo the typical aluminum extrusion bed for the CNC because I had something just as flat: wood! The previous owners of my home included a woodworker, and my engineering bay was his old woodshop. I happened to have some scrap boards that were absolutely fine lying around, so I decided to use some of that as the combo bed and spoilboard (spoilbed? spoilbed). To attach it to the Ender, I designed a bracket to couple the spoilbed to the metal platform containing the belt holder. The bracket also had counterdrilled holes designed so that four M4 X 40 mm bolts could be run through into the corresponding holes in the platform. I reused the metal springs from the headed bed, but I printed new bed levelers out of red ABS. For the bracket I used ABS-GF with three walls and 40% gyroid infill. As it didn't need to be super strong, just hold together, I designed a bitchin' hexagon pattern into it that you only get to see when you're swapping out the spoilbed. Oh well.