Of course you will need a second extrusion train. Besides that, the good news is, the most important parts to be modified are already in your UM2. Basically you need to cut the bottom-plate in half, creating 2 levers. Modify them, so they could rotate. Bolt a bearing (W 627/3-2Z) on the front side of the top plate, used for the switch plate. The only part left is the cam-plate.
In my case it's a laser cuted PS plate. It surprisingly surveys already multiple days, none stop printing with 240 degrees nozzles & 70 degrees heated build plate.
Then on both sides of the printer, you need a 'switching-block'. Just a simple printed part should do the job. An other interesting working solution: use the UM side bearings as switching location. Then you only need a 'X' movement to do the switching action. But I leave this to your own imagination.
#define EXTRUDERS 2
#define HEATUP_POSITION_COMMAND "G1 F12000 X110 Y10"
Prime position = "G28 X115 Y10"
Pause position = "M601 X115 Y10 Z%i L%i"
These positions are changed, so when you do switching in the corner, you don't want to hit these positions while priming/pausing..
|For the first trial I'm using the 'old' Cura 15.04 version and created a VBA-program (Excel) to modify all 'T0' and 'T1' commands, adding the right switching movements. Now all updates & modifications are done, it's time to start the first dual print.|
|A colleague helped by creating nice Cura 3.x machine defintions. It's a mix between UM2 & UM3 settings. Just copy the cura definition file and move the files in the right directory of your cura install. With every new Cura installation, you have to do this again.|
Now the dual color printer is ready, it's time to print something... So I designed some duplo compatible characters and printed the name of my new born son.|
Printing took about 7 days none stop printing (0.1mm layer height), w/o any switching problems.
Uploaded most characters to thingiverse and youmagine.com.