A CNC router will allow us to cut shapes from substantial materials, such as solid wood, mdf, plywood and so on, as well as to cut materials that a laser cutter cannot handle (mainly metals, copper-clad board, aluminium and so on).
We've gathered a lot of the hardware required so are looking at different gantry styles and the pros and cons of each. Here's a quick list of the main components: stepper motors (Matt has some big beefy 3A steppers) control board (TB6560 from eBay) skateboard bearings acme threaded rods and nuts tubes for bearing runners milling machine (Dremel, electric drill, wood router) routing bits (straight, rounding over, multi-direction milling bit)
We've scoured the internet and have used a number of different designs for inspiration. At these early stages, we're putting together the bed and gantry before mounting the stepper motors and router tool. The datasheet for the stepper controller is at http://www.savebase.com/infobase/downloads/TB6560/TB6560AHQ_AFG_datasheet.pdf
At first we thought about the mini-milling cnc machines: these use a fixed router and a moving bed. The problem with this design is that the cutting area is roughly half the size of the bed (so to cut a 60cm A3 sized board, we'd need a 4 foot bed!). Because of space restrictions, we decided that we needed to be able to use as much of the cutting bed area as possible so settled on a moving gantry style design (the router moves in all X,Y,Z directions and the piece being cut remains fixed to the bed).
Although the design is still being decided, the X axis (longest) rails will probably be the same as in this design: http://www.cncroutersource.com/support-files/cnc_router_jgro.pdf
It's basically an L shaped bracket, with skateboard bearings mounted at 90 degrees to each other. The bearings run along a rounded metal rod. The tubular rail means a minimum surface area is actually in contact with the bearings, resulting in lower resistance from friction.
We've seen modular cnc machines that use exactly the same design for the X and Y axis - we may yet do the same, leaving only the Z axis to be decided upon.