Comment Re:Unit can also do 3d printing (Score 1) 258
I am thinking of adding an extruder head to my little taig cnc mill. There is reprap software that will drive a stepper-motor extruder feed as a 4th axis which makes it pretty easy to control with EMC2 and a 4-axis stepper controller. It should be possible to do work with complex overhangs that wouldn't easily be possible with the mill alone, and definitely acheive fit and finish you'll never get directly from the extruder alone.
As long as you know the offset between the tip of the tool in the spindle and the tip of the extruder nozzle, it would be easy to alternate extrusion and milling passes. Still,any problems in one operation will tend to cascade to later stages, so extruder reliability is pretty critical. Most CNC mills will probably have table/gantry movement speeds on the slow side compared to extruder-specific machines, but i don't think this is a major issue in practice.
Workholding will need attention - the extrusion process places almost no load on the workpiece itself, while any kind of cutting or drilling operation will throw the work across the room if it's not clamped, bolted or glued down. Its possible the self-adhesive properties of the extruded ABS or other plastic could work here, but i suspect this will not be enough. Most models would probably need to start with extruding a clampable base for the object.
For smallish pieces, its often going to be just as easy to mill with work clamped in a rotary table, which allows you cut things that would be very difficult to maintain alignment on otherwise. Making jigs to keep work aligned in place for machining different parts of the piece is also very common, so its unclear what real-world use such a hybrid machine will have, compared to using 'traditional' methods to machine the same part.
I think the idea has legs though, and a small cnc mill will offer a lot more accuracy than the makerbot or reprap does due to more rigid construction and usually very good anti-backlash.