Wanhao i3 Backplate with Dual 50mm fans

I started with chinkel's replacement backplate to get basic dimensions and tab placement, but this geometry is all new.

The main improvements in this one are a stiffer part overall, cleaner power plate placement, and more protection for the fan blades. The fan openings also continue the hex pattern of my extruder fan grille, thing:1504489.

Strength comes from 2mm high, 2mm wide ribs all around the perimeter/tabs and to the power opening.

Since the tab and power plate screws are all m3