It took me about 2-1/2 hours to build the 3D printer and about half-hour to level the platform. I tried to print a sample file from Simplify3D but the printer crashes into the corner while homing and I have under-extrusion problem. The extruder has stepper motor turning a large gear that pushes filament out the nozzle. I don't know the gear ratio. How can I fix the problem?