Two pieces of software may be used to create the tool paths, or GCode, for multicolour printing; RepRapPro Host and Slic3r. RepRapPro host is tremendously versatile, and allows for different areas of the part to be assigned different properties such as temperature or infill percentage. Slic3r on the other hand is not as versatile, but is recommended in all cases for mono prints and generally it produces better quality prints.

If you are new user it is recommended that you start with Slic3r, and progress to the extra versatility of host if required.


Installing Slic3r

You should have Slic3r already installed from commissioning your printer as a Mono printer. Make sure you have our Profiles installed too. Instructions are HERE.

To run Slic3r, simply open the application from your applications folder.


Selecting your profile

Before Slicing, you first need to select the appropriate profiles. These are chosen from the drop down boxed on the main window of Slic3r.

First select the printer profile from the right hand side of the window. For a Tricolour Mendel select “M-PLA-05-03-1mc”. This corresponds to a Mendel printing PLA, with a 0.5mm nozzle and a layer height 0f 0.3mm

This will then produce more drop down boxes for the filament settings, one corresponding to each extruder. Again choose the “M-PLA-05-03-1mc” filament setting for each extruder. Finally choose “Mendel PLA 05 nozzle – mc” from the print settings drop down menu.



Creating an AMF File

Where as single material prints require STL files for printing, multimaterial files require AMF files. However, AMF files have not yet been adopted by most CAD packages and so STLs need to be converted. If you are designing parts that need to be printing in multiple colours, you need to ensure that the STL files produced share the same coordinates and origin, such that Slic3r knows their relative positions.

To create an AMF select the “Combine multi-material STL files” from the file menu:


You will be presented with a file window to choose an individual STL. You need to navigate to your STLs in the order the corresponds to their extruder number. Select your first STL, then click ‘Open’. The file window will open again; select your second STL, then click ‘Open’. The file window will open again; select your third STL, then click ‘Open’. The file window will open again; once you have selected all the STLs you require, hit the cancel button. A new window will open allowing you to save your AMF file; give it a sensible name, as it usually gives it the name of the first STL you chose. Then click ‘Save’.

The order you choose the STLs relates to the extruder each part will print from; the first STL you pick will be assigned to extruder one, the second STL to extruder 2 and so on.



You may now add your print to the build area. Choose ‘Add’ from the build area, or from the main window, and navigate to your AMF file if your are producing a multicolour print, or your STL files for a single colour print. If you have multiple files, you can keep adding AMFs/STLs to the tray and position them using the window to the left.

Slic3r file loaded.png



To slice your files, simply choose export GCode, and save the file to a convenient location. It is highly recommended that this is copied to an SD card for printing rather than over USB. This file may then be printed from pronterface in the usual fashion.


Switching back to mono printing

If you want to print single colour parts again, you just need to change all three Slic3r profiles back to the mono print profiles; Printer, Filament and Print settings.

  • Tricolour: Notice the ‘Filament’ setting has 3 filament options

  • Mono: If you have selected the correct ‘Printer’, it will show just one.

When it comes to printing, you may need to reset the printer if you have issued any tool change commands (T0, T1, T2). If you have, printing mono gcode should print using the currently active extruder; the other extruders will sit at their standby temperature for the whole print. If you get a message ‘cold extrusion prevented!’, you may have a mix of profiles selected in Slic3r.