Printable Inkjet Head
by adrian-bowyer, published
This is an inkjet head that can be made from 3D printed parts plus simple easy-to-obtain components. It requires no machining to make it - you just need scissors and a scalpel.
This is experimental, and in particular it needs development on its driver electronics. But it does work.
There are full instructions and a bill of materials for this on the RepRap website here: http://reprap.org/wiki/Reprappable-inkjet.
Update - I've added my version of madscifi's OpenSCAD take on this (see below) that allows you to have different piezo diameters. Mine also allows you to decide if you want two O rings or one.