Poltur XL 300x200mm Heatbed add-on

this design is for adding a purpose built low cost 300mm wide heated build platform to my Poltur XL printer design.

this design uses...

2x 600mmx8mm linear round rails and bearings
http://www.banggood.com/200600800mm-x-8mm-Linear-Rail-Shaft-Rod-with-Bearing-Guide-Support-and-SCS8UU-Bearing-Block-p-1104573.html?rmmds

1x 200x200 12v silicone heat bed matt
http://www.banggood.com/12V-200W-200mmx200mm-Waterproof-Flexible-Silicone-Heating-Pad-Heater-For-3d-Printer-Heat-Bed-p-1123501.html?r