3D-printable postcards: Because paper is so last millennium (Part II)

Have you seen my article on 3D-printed postcards? Here I will show you all the tricks I use for them and some more tricks that you can use to create your own printable “papers”.

Teaser: you could use the following PrusaSlicer tricks for more than just postcards! (Nobody sends those anymore, anyway, what am I, sixty years old?)

I love 3D printing and I love sending postcards to my friends, so this is just a natural combination. The postcards are designed in PrusaSlicer and, although they're multicolor, they can be printed on a single-extruder printer. They are created using Text and SVG modifiers. In this article, you also find out how to implement this together with a lithophane.

As a reminder, in case you haven't seen the first article:

It arrives! 📫

To prove my point, gaze upon this postcard that I sent to our office!

If you want to go the easy way, you can use my model and follow the instructions in Part I of this article.

Now, let's dive directly into PrusaSlicer.

How-to guide 🪛

A lithophane postcard

I will show you the settings and workflow on something that I'd usually send as a postcard - a lithophane. I've learned about lithophanes from this blog post and I like using them as postcards, little gift cards, stuff like that.

See the result: (This is the Falkirk Wheel in Scotland, by the way, amazing place!)

The AI overview says that “a lithophane is a three-dimensional image created by varying the thickness of a translucent material, such that when a light source is placed behind it, the image appears in shades of light and dark.”

It works best with light colors, such as the Prusament Pristine White here, which is also the best for a postcard. I like using this webpage to create a lithophane. These are the Model setting I'd recommend:

Maximum size: 150 mm (common postcard size)
Thickness: 1 mm
Thinnest layer: 0.2 mm (because we slice it with 0.2 mm profile)

In the Image settings, the first slider should be set to Positive image. Leave the rest of the settings on default. Upload your picture and then download the model. This gives you an STL file. It has a long generated name, so consider renaming it before opening it.

Then, open it in PrusaSlicer.

What we need is to create the back side of the postcard, where the text will be. Firstly, add a box as a part of the object (lithophane).

Then, set the size of the box to be the same as the lithophane in X and Y and 0.4 mm in Z.

Next, align the two parts so that the box is lying on the print bed and the lithophane directly on top of it. This means dropping the box to bed and setting the object coordinates in X and Y to be the same for both parts. The lithophane needs to move 0.4 mm upwards - this is best achieved when you change to Part coordinated and translate it by this value in Z.

Now, your postcard is ready for some text and pictures. But before that, let's set up the trick that makes the postcards possible - manual color change using virtual extruders!

Printers → General → Capabilities → Extruders: 2, Single Extruder Multimaterial: Yes
Printers → Custom G-code → Tool change G-code → Type in: M600; Filament change
Print settings → Multiple Extruders → Wipe tower → Enable: NO
Plater → Right-side menu → There will be two Filaments → Use the same material, assign different colors by clicking on the color field next to the filament type

With this, we are ready to write our postcard. Oh, and by the way, don't forget to save your project.

Rotate the view to see the bottom of the card. Right-click the object and add a Text modifier. The Emboss menu appears on the left side. See the settings below:

Write your text into the text field. By pressing Enter you add a new line.
Use a suitable font - sans serif type, consider making the text bold. The default height if fine but feel free to play with it.
Depth: 0.4 mm - this means it will be printed in two layers. This is optimal for readability.
Alignment: Top and right makes it convenient for positioning the text field.

Leave the rest as default. You can use and rotate the text as any other object in slicer.

In the right menu, assign the text to filament #2.

In the same way, add other modifiers:

another text, saying hello to Grandma
a dividing line in the middle, to separate the address and the text - add this as a thin, long box with the height of 0.4 mm, assigned to the second filament
a little heart to let Grandma know that you love her: Right-click → Add modifier → SVG → the SVG menu appears on the left side → Choose an SVG file, change the depth to 0.4 mm and adjust the size, move it, rotate it as needed. Don't forget to assign in to the second filament.

Important! All the modifiers must be placed on the sheet, and they must be 0.4 mm deep. This way, they will only modify the box that is 0.4 mm thick. The lithophane must be 0.4 mm above the sheet - directly on the box. The shifting gets sometimes confusing in slicer, but we will check the G-code to make sure we got everything right.

Ready? Let's slice it!

Looking good! Check out the first layer using the bottom slider:

As you can see, the printer will start with the white “paper”, then change to the black filament for the modifiers. This is important to know, because you will act as the multi-material unit, and you need to know the order of the colors to perform the color changes.

How the printing works

When you're happy with the result, send it to your printer. At the points of the color changes, the printer will pause, unload the filament and wait for you to load another one. It will wait infinitely, but it's better to wait around and change the filament right away. The “Sliced Info” tells you the estimated printing time and the number of filament changes.

Mind that this is a bit of a hacky way for multicolor printing - therefore the printer is a little confused.

When you start the print, it will tell you that the loaded material is the wrong type - you can ignore that.
Then, it will do one filament change after printing the purge line - but you want to keep the “paper” color (white). (or change to it if you forgot to do it before)
In this case, you start with the “paper” (white), then change the filament in the following order: paper (white) → text color (black) → paper (white)

If you change the printer, make sure to TRANSFER all the preset changes - and I mean ALL of them.

Why do I emphasize that? Because by default, Slicer does NOT transfer the Custom G-code (as you can see above). But this is the little trick that makes the manual color changes possible! Without it, the printer will print everything in one color. So, make sure to check that checkmark and then you'll be alright.

Get creative! 🎉

Now that you know how to set up these single-extruder multicolor prints, you can create much more than just a postcard.

You can create a card from scratch and cover it in SVGs, text, or shapes to your liking. You can use different colors and even different materials.

You can of course have more than two colors - just change the number of virtual extruders under Printers → General → Capabilities → Extruders: #. But I warn you, too many filament changes are really annoying, you don't want to do that in every layer. Always check the order of the colors in the G-code preview in slicer and note it don't to perform the changes correctly.