First Layer Multicolor Printing
Using a Standard Printer

Automatic machine swapping of filaments is a common way Multi-Material 3D printers get several colors embedded into a single print. For a standard non-MM printer, you can achieve the same results but it requires manual labor due to not having the ability of automatic switching. With the extra amount of work involved attending to the print, MM effects with a standard printer are best suited for projects where the color changing happens on very few layers. 

Items like keychains, tags, signs, business cards, guitar picks, etc. are perfect for this since they can be totally smooth on both sides, avoiding the scratchiness that comes with top layer color swapping. You can even add colorful text on the bottom of tall objects, such as including the designer's name on a vase. 

For this guide we will be using Prusaslicer to achieve the desired effect. Other slicers may be able to accomplish the same goal but I have not tried them. You can download it here: https://www.prusa3d.com/page/prusaslicer_424/
This guide assumes you have a basic understanding of how to use Prusaslicer's standard operations, such as opening a new file or changing printer settings. 

The way it basically works for the project in this guide, is that the model will print the first color on the first layer before pausing and prompting you to unload the previous filament and insert the next color. Prusaslicer currently doesn't have a preset to accommodate this specific arrangement automatically so this guide will explain how to set it all up and then walk you through how to print a simple MM Prusa keychain.  

Click here to download the files we will be using for this tutorial. The zip file includes 6 stls and 1 emf file. Unzip the files so they are ready to go.  

In Prusaslicer, make sure you have it set to 'Expert' mode at the top right in order to see all available settings, then proceed with the steps below (they can be done in any order). 

Set number of extruders

You will see the 3 extruders appear on the left settings tree. Clicking on them will allow you the option to select the colors they will represent in the preview screen. 

Insert G-Code

For this technique to work, a snip of G-code must be added.

{if layer_num > -1}

M600

{endif}

Disable wipe tower

Since the color swapping we will be doing here only happens on the first layer, there is no need for a large wasteful wipe tower for purging and priming the nozzle. Instead, we will use a custom version that uses minimal material, explained later. 

Go into Print Settings and into Multiple Extruders section, and under Wipe Tower uncheck the box so it will be disabled. 



Load MM model

When using a multi-material model for this technique, you will need to load it into the slicer in certain way. Since MM models are split into multiple files representing the different colors to be printed, to add all of the parts that make up the complete object you need to select each of those parts in the file browser and add them to the slicer all at once. 

Tip: If you are trying to create your own MM model and find that the parts don't align properly in the slicer, the parts need to have the same origin point when aligned correctly, which can be set in your modeling software. 

Add nozzle purging wipe pads

One challenge of multi-material printing is that swapping filaments can involve undesirable oozing while the printhead moves to resume printing. This build up from the nozzle leads to an ugly blob of material placed where the nozzle resumes, potentially ruining detail-focused prints.  Even using the skirt to purge newly changed material doesn't quite help, because the oozing nozzle returning to the print will always touch the model first before touching the skirt.

To avoid that issue, we will be using small rectangular pads that will be added to the slicer as a MM model in the same way the keychain model was added. 



Lastly, slice the model, and if everything looks good go ahead and print it! 

Once a color change happens, the printer will automatically pause and prompt you to remove the old filament and insert the new color, and allows you to purge the color to get it right before resuming. On resuming the print, try to remove excess purged material before the print head starts moving so it doesn't interfere.