Sanding Paper is expensive and don't last that much. Sanding belts are affordabe and pretty strong because they need to hold a lot of torque and speed. Sanding belts last a very long time because they have a strong fabric back. That's the perfect accessory for sanding blocks.
I wanted a simple sanding block, perfectly stiff and strong, not too long to be printed with not muck filament consuming through. Two simple parts interlocking that makes a pretty good tool by the way...
Operating manual in real time ^^ : http://youtu.be/YRtQ1YqoEB8
The original model is meant to be used with 475x75mm belts (Bosch, Makita, Skil, Black & Decker, Parkside...), but you can easily scale it for other belt size, just do the maths.
Prusa I3, Tarantula, CoreXY, FLSun Delta.
Plan on perimeters only for strenght and fast printing. The parts are optimized for 3 perimeters out of a 0.4mm nozzle. (3 inner + 3 outer) Enjoy.