I took some ideas from this project: http://www.thingiverse.com/thing:962283 and then i redesign it from the ground....
To make this you need:
1 x Spring (12mm
...Plus lenght, personally i reused my prusa i3 bed spring)
1 x threaded rod 6mm
2 x nuts
1 x Microswitch (i used this one: http://www.ebay.it/itm/201058738299?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT)
1 x hexagon bar (measures 14x145mm - usually used to hide the support of shelf : http://www.ebay.it/itm/Mensola-a-Scomparsa-Fischer-art-CPF-14x145-mm-conf-1-pz-/231464646669?hash=item35e45e380d:g:l-gAAOSw1ZBUx8Ww)
hope you like this work ;-)
