I wanted to use the space on top of the IKEA Samla bin that's living on top of my Snapmaker U1 (see here for the mount). So like any good 3D printer owner, I slapped some gridfinity on it.

This gives you a 8x12 gridfinity baseplate that slots into structural molding of the samla bin. I modeled it to be a somewhat tight fit with my particular bin, but I couldn't test it with others. It is broken into quarters to fit the buildplate of the U1. The parts include holes to connect them using m3 bolts, however I found them to not be strictly necessary.

I printed mine in PLA with 5% infill, but if you're planning to print higher temp materials on your U1 something more temperature resistant like PETG might be a good idea.

I included the FreeCAD project, feel free to modify and remix. I used FreeCAD 1.1 with the gridfinity workbench installed, so you'll probably need at least that.