Got the 3off E3dTitan extruders mounted in a sort of flying arrangement so now the printer has grown by another half metre in height. I've also added a means of mounting filament spools (2 lengths of 32mm waste pipe). Tip to toe, it's now 1.7 metes tall.
I'm really chuffed that I've ended up with with 300mm long Bowden tubes for a print area a shade under 400mm square on a frame which is 600mm square and over a metre tall.
I don't know how to add pictures to posts - perhaps someone can enlighten me. Meanwhile, I've added folders named "Extruders" and "Wiring" to the shared google drive folder - link here. https://drive.google.com/folderview?id=0B_MwtHtQR_ZvSkZlRWphTnJ3X0k&usp=sharing
Big thanks to AussiePhill for the idea but also apologies for not using his STL. I needed to tweak the design and it was just easier for me to start from scratch with OpenScad which is all I know how to use.
The extruders are mounted together on a custom mount which is suspended above the centre of the bed on a pulley arrangement with a counter balance weight (printed container with lead shot). This allows the whole thing to fall when the print head is at the extreme corners but the rise again to "lose" the Bowden tubes when it is directly above the centre of the bed. The combined weight of the three extruders with their stepper motors and mount is 905 gms, the counter weight is a little more than this to overcoming and friction and "sticksion" and ensure that they rise up when needed to and prevent the Bowden tubes from buckling. So, there is a slight upward pull and I've fitted cords between the extruder mount and the X carriage so that this pull is not transmitted to the Bowden tubes which are slightly under compression, keeping them firmly attached at both ends.
Inevitably, there is some drag on the X carriage due to the wires and tubes but it is tiny compared to having to lug 900 gms of extruders and steppers around.
A more elegant solution might be to mount the counter weight on a vertical linear rail using a bit more V slot, but I'll wait until I've tested the printer to make sure it's viable.
The wiring is about as far as I can get - just needs the Duet (batch4) but my daughter's wedding is only a couple of weeks away so further work will have to be put on hold. I've braided most of the visible wires and fitted printed labels covered with clear heat shrink. Where possible, I've run the wires inside the Vslot and fitted cable covers which makes quite a neat job. I've used flexible conduit for all the wires from the hot and and x carriage. This still looks untidy to me but there are a lot of wires (heater, pt100, xmin, xmax, hot end fan, print cooling fans, z probe and of course 3 extruder motors) and they have to be long enough to reach all 4 corners of the print area.
I've added separate micro switches to the extremes (max) of all the axes and connected them in series to try and prevent crashes during commissioning or in the event of a probe failure. I've added a separate emergency stop button too. The mains to the heated bed is in a flexible cable chain. The bed plate is earthed, and also connected to the frame which is also earthed in two places and I've fitted an RCD plug to the mains inlet. All the mains wiring is inside a printed enclosure so all in all, it should be safe.
