The heated bed is a very important element in 3D printers in order to print with plastics that shrink when the cool down, like ABS.
It is also very helpful when printing with other plastics like PLA, where it provides an extra adhesion, increasing the number of successful prints.
Although it is technically possible to print directly over the heated bed, we recommend to build a sandwich-like structure: beneath the bed an isolating material, for example wood, and above the bed, with the thermistor facing upwards, a layer of thermal conductive material
, and above that layer a mirror as building surface.
MK3 round model with 220mm diameter is suitable for Deltas and Rostock.