Heated bed blues
Reprap 3D printers can benefit of having a heated bed because that helps preventing part's warping. When a part is printed, it is done depositing layer after layer of fused plastic filament. Either PLA or ABS, these fused filaments will experience some contraction when the melted filament solidifies and cools down. This effect will be more dramatic the faster it happens. And the end result is that some of your printed parts will have a round bottom instead of a flat one. And that is if you are lucky, as some parts will completely detach from the print bed mid print and they will be totally ruined. So we use a heated bed so the print bed is kept at a relatively high temperature. This way the filament will cool down not so fast and hopefully the parts will stay well grabbed to the print bed even in the corners. There are several ways of creating a heated bed: a printed circuit board with a long copper track zig-zagging the surface that will create a resistor. An aluminium p