The Buildlog.net Open Source Laser cutter/engraver just added 3D printing to it’s capabilities. The printer system uses the existing CNC motion system of the laser cutter along with standard RepRap electronics. A quick release plastic extruder carriage is added to the existing gantry.
The upgrade project is called the Chimera Project because this is a hybrid of two self replicating machines. The parentage of the parts gets a little blurred. A Chimera is a animal descended from two genetically different animals. The laser is self replicating by making all its non off the shelf parts. Adding 3D printing takes that another step forward. The electronics were packaged outside the enclosure for development, but will be moved inside soon.
Changing modes is quick and simple. Swap the control cable, attach the extruder carriage and you are ready to print. You can even leave the printer carriage in place if you don’t need to use the full width machine when laser cutting. The total upgrade cost is less than $200.
The RepRap electronics can actually control the laser cutter with no modifications to the hardware or software, but the lack of acceleration parameters in the RepRap control system limits the speed the laser carriage can move before it becomes to jerky.
Already in the works are a tangential knife cutting head, Pen plotter and Dremel tool head. The entire system is open source and well documented. Starter kits for the laser are available and the 3D printing parts are coming soon.
Also see a build log for a project going the other way: a MakerBot printing a laser cutter.