If you put your hand into a nano-fabricator, all you are going to pull out is a bloody stump. Not only would your hand be considered raw materials, nano-fabricators have a taste for blood ;) /joke All joking aside, I remember watching a good video of how a nano-fabricator might work. It involved a multistage process. First, the atoms are assembled into simple molecules. Those molecules are moved to the next assembly level above where they are assemble into more complex molecules. Those molecules are moved to the next assembly level above it and further assembled, and so on. Eventually, they start assembling the final product, where every molecule or component is added to the final product. So if you were to yank out a half finished hat, you would get a hat that probably looks like it was cut in half. I wouldn't recommend opening a nano-fabricator though, as you might let dust in. For a machine with tools to work with atoms, dust are like giant boulders and can cause serious damage if they get inside. I don't know where the vid I saw is right at the moment. I'll post it if I find it.

As I describe them, standard CMs are like microwave ovens. They have a vacuum sealed compartment where various robotic arms and nanostructures work, and you can watch it through the diamond window. Opening the door while the CM is working is going to put it in emergency shutdown and quite likely damage delicate subsystems. When it is finished it retracts the work surfaces, repressurises the compartment and with a "bing!" opens the door. The product is typically warm to the touch and often surrounded with easily disposable scaffolding material (put it in the recycler receptacle below). And then there is that lovely "new nanoassembly smell". If you have ever seen a 3D printer working, you will know that the actual building even of a simple object like a cube consists of nontrivial patterns. Quite entrancing to watch. The algorithms can be quite complex. If there is no need for enormous strength the CM will not fill all of the object but will leave empty spaces honeycombing it. If the object needs to have some heft they can be filled with water. The internal structures can be extremely complex and optimize for strength and resilience like cancellous bone, with thin arcs and sheets following lines of force. How objects are built up depends a bit on the CM design. Oldfashioned fabbers have writing heads moving above the workpiece. A classic nanoassembler model might have a sheet of assemblers where the object is magically extruded from "nothing". A more efficient convergent assembly would have tiny robotic arms assembling pieces produced from small compartments containing tinier arms taking pieces from smaller compartments with even tinier arms... A more general CM might have internal nanoswarms or nanosuspensions in a liquid, growing the object inside out. CMs generally take a decent amount of power: they will have fans or even need coolant pipes. Think of them as ovens. To save energy they often make use of nano lego-pieces and pixels: standard modules that can be assembled with a minimal amount of energy and effort, provided in toner-like cartridges or via the feedstock pipes.

As i suggested in another topic ([url=http://eclipsephase.com/node/3388]here[/url] ) i view CM as large scale engeneering progect done by pico-nanoscale workers, for pure economy of energy i suppose the use of fractal robotics arms. The arm have less travel time from start position to the nucleating site of the obyect and work as logistic chain for feedstock and coolant, on the branch of the arms there are molecular sorting-assembly sites that expose the currently need elements and smaller digits catch and place them, this kind pf process can be fractalized too, using a part of arm as molecular assembler, another as picoscale composer and glueler and up to the final obyect. I also suppose the use of prefab feed, a lot of objects probably use a limited range of common structures as structural material (nanotube, alluminium fibre, diamondoids...), the disassebly phase can conserve this molecule for reuse. As visual effect you have some arms extending to the centre of CM assembly volume and begin to "buzz"forming nucleating sites that expand to the final obyect, if you stop the process you have different results depending on the current completed passage: from a dust of nucleating sites to an almost finished obyect. As rule in my game CM are filled by liquid for cooling and, in gravity enviroments, for reduce the needs of lifting or supporting the forming obyect.