In search of the 5th Element,it's no secret that the reason i'm making a 3D printer, is because a 5 axis mill is a little impractical at the moment, cost & space being the limiting factors, but hopefully one day soon I can prototype parts in aluminium on a 5-axis machine.
So while 3D Printers are happy enough with 3 Axis, a combination machine could benefit from the extra add ons to explore alternative setups for milling, routing, or turning, or for use on the photography video side, as a mini motion control/ timelapse rig.
To date a number of alternative linear axis have been designed, a few are currently being produced, we have the 4 rod Z column, and an addition 2 column Z for the other end of the arm, if required. The table Y-axis is belt driven, but as the bolt on second Z Axis going to be a leadsrew driven item, possibly housed in perspex initially, it will probably be developed to also function as a bed actuator. This will probably be most useful for adding the 4th & 5th axis.
The quick release 2 rod X axis arm can also be reconfigured, horizontal or vertical, front or side mounted, also looking at relocating the X-axis stepper to test out a few other ideas, a rear mounted motor would look quite cool and maybe distribute the weight better, acting as a counterbalance for the arm, if the second Z-axis isnt used, but for heavier carriage setups the second Z would obviously be required.
Another version of the X axis has the head on the end of the arm, and the whole arm moves, add this to a rotating Z-axis and you've got yourself a pick n place robot.