A lot of builds here have the bed with rails along the bottom and the gantry sitting on top of it. I have been looking at 3D printers and see a few designs where the 'gantry' runs on rails above the build table. Is there a reason CNC routers dont adopt this design more? At first glance these seems like a good option because the motors and other components would be above the work surface and out of the dust. The downside might be that the gantry above the bed might make adding material on the bed would be harder or blocked by the gantry support. Can anyone comment if they have tried this?