Z-axis center clamp for Portabee 3D printer

This is a clamp to keep the Portabee 3D printer in the center of the box I've built for it.

More details here: http://www.igorkromin.net/index.php/2013/05/26/a-clear-acrylic-box-for-the-portabee-3d-printer-part-1-making-the-box/