cOssel Delta printer made by 6-8th grade class at Steppingstone School. Notice the following modifications: 300 mm square 1/4" aluminum bed with a 12X12" bed heater glued to the bottom with 1/4" thick 300 mm diameter glass as the printing surface. Files will be uploaded shortly. Also, we printed a planetary gear drive for the extruder (http://www.thingiverse.com/thing:39558) and have modified the plate sliders to accommodate mechanical end stops.
An advantage using the aluminum bed is that auto-leveling becomes a snap as the hot end itself in contact with the bed closes the Z-min endstop circuit. Adjustment for the glass is a simple subtraction of the Z height value.