Two-Colour Prints With a Single Nozzle: The Colour-Change Method

The cheapest upgrade to your prints isn't a multi-material unit. It's learning to change filament once, at the right layer.

A name sign with white letters on a black plate, a keychain with a coloured border, a QR code that actually scans: all of these look like multi-material prints, and all of them can come off a single-nozzle printer with one swap. The trick is in how the model is built, not in the hardware.

Why it works: colour by height, not by area

A single-nozzle printer can only print one colour per layer. So a two-colour print with one nozzle has to follow a simple rule: everything below a certain height is colour A, everything above it is colour B.

That rules out some designs. A logo with red and blue areas side by side, at the same height, can't be done this way. But most text projects fit the rule naturally:

• A plate or border at the bottom, in one colour
• Raised letters on top, in another colour

The generators on text3dmaker are built around this. The border on a nameplate sits entirely under the text. The QR code's dark modules start exactly where the light base ends. The initial name sign stacks the letter, the outline and the name in three bands. There's never a layer that needs two colours.

Finding the right height

You need one number: the height where the second colour starts. The initial name sign generator shows it in its panel. For anything else, move the layer slider in the slicer preview until the first layer of letters appears.

Say the border is 1.6 mm thick and you print at 0.2 mm layers. Layers 1 to 8 are border. The first layer of letters is layer 9, which starts at 1.6 mm and ends at 1.8 mm. The colour change goes before layer 9.

Two practical rules:

• Dark over light covers faster. Black letters on a white plate look solid after two or three layers. White over black needs four or five before the dark stops showing through. If you can choose, put the dark colour on top.
• Give the top colour at least 0.6 mm. Below that, the first colour shows through at the edges.

Setting it up in your slicer

Bambu Studio and OrcaSlicer. Slice, open the preview, drag the vertical layer slider to the first layer of the new colour, right-click the small plus icon and choose Add color change. You can also choose Add pause if you prefer to swap by hand without the printer's automated routine.

PrusaSlicer. Same idea: move the slider to the layer, click the orange plus icon. That inserts an M600 colour change. Right-click the icon for a pause or custom G-code instead.

Cura. Go to Extensions → Post Processing → Modify G-Code, add the Filament Change script and enter the layer number. Cura counts layers from 1, so check the number against the preview.

If your printer ignores the colour change, its firmware probably doesn't support M600. Use a pause instead: the printer stops, you unload, load the new colour, purge a little by hand and resume.

With an AMS: fewer swaps, less waste

An AMS or MMU can change colour on every layer, which is exactly what makes it wasteful. Every swap flushes filament through the nozzle and adds time. A three-colour sign printed with colours side by side in every layer can mean two swaps per layer. Over 40 layers that's 80 swaps and a purge tower bigger than the sign.

Build the same sign in height bands and the AMS swaps twice in the whole print. That's why the initial name sign has a mode called Multicolor by layers: the parts are split by height, each part is assigned to its own AMS slot, and every layer is a single colour.

One Bambu Studio detail worth knowing: when you open a 3MF that wasn't saved by Bambu Studio, it shows a notice that only the geometry is loaded. It keeps the parts and their assigned filaments, but ignores any colour changes stored inside the file. If you use the single-nozzle file in Bambu Studio, add the colour change yourself in the preview, as described above. The layered multi-part file doesn't need it.

Checklist before you press print

• The second colour starts at a height that's a multiple of your layer height
• At least three layers of the top colour (0.6 mm at 0.2 mm layers)
• Colour change or pause inserted before the first layer of the new colour
• Enough of the second filament ready: for text it's usually only a few grams

That's the whole method. One swap, no extra hardware, and prints that look like they came off a much more expensive machine.