This is what I created to hold my I3 Rework to my 3/4 inch board. Your printer must be screwed into something (table or separate board) to use my other I3 Rework addition – http://www.thingiverse.com/thing:395526
I use 8 of these clamps to securely hold down my I3 Rework via one #6 wood screw each (3/4″ length in my case). Put one each right next to the aluminum frame (a total of 4) and one each at all four corners (a total of 4) and the printer will not budge or have a tendency to walk around at high speeds.

Print these with no less than 35 percent infill or they will collapse when tightening the screws down. From my experience I suggest an infill of between 45% and 70% depending on the quality of the ABS.