Two printers this autumn are built around the problem from the purge tower post. The Creality K3 opened US pre-orders at $849 this month, with Europe expected in December. The Snapmaker U1 went on sale worldwide in April. Neither one flushes a shared nozzle to change colour. They keep four filaments loaded in four separate nozzles or toolheads and swap between them in about five seconds.
Both promise up to 85% less waste. That is a vendor number on a vendor test print. I wanted the number for a map, so I counted.
The model I took apart
I used the Matterhorn model I published on Printables. It is 7 km across, printed at 150 mm with no exaggeration, and stands 54.4 mm tall. It has three parts: terrain, raised contour lines every 100 m, and rivers and lakes cut into the surface. At 0.16 mm layers that is 341 layers.
I opened the 3MF, read every triangle, and recorded which layers each part touches. A printer only changes colour when a single layer holds more than one, so that is the whole question.
The range on the right is the slicer's ordering. A slicer that prints the same colour order on every layer pays to go into each extra colour and back out again. A slicer that starts each layer on whatever colour the last one ended with, and ends on one the next layer needs, pays roughly once per shared layer. Where a real slicer lands depends on how it orders colours.
Steep mountains are the worst case
The Zermatt model in the purge post had contours in only 19% of its layers. Here it is 66%. The difference is slope.
A contour line follows one height, but the raised ribbon is 0.7 mm wide, and on a face as steep as the Matterhorn's that width spans well over a millimetre of height. Add the ribbon's own 0.6 mm and each line sits in about ten layers instead of four. Twenty-three lines times ten layers covers most of the print.
Rivers are worse in a different way. A stream runs downhill, so a single blue line passes through every height between its source and the valley. On a mountain the water colour turns up in a third of all layers, even though it is a tiny fraction of the surface.
What that costs on a single nozzle
On a single-nozzle printer with a filament feeder, every change flushes the old colour out. The default flush on common machines is around 8 g per change, and well-tuned setups get it to 2–5 g.
Even the best ordering, at the default flush, puts more than four times the model's solid weight into the purge tower. That is not a fringe case. It is a mountain with contour lines and rivers, which is what most people want a map to have.
Yosemite Valley, a flatter model, is better but not good: 153 layers, 134 of them shared, and 246–378 changes for the same three colours. That is still around 2 kg at the default flush.
What a nozzle changer changes
On a four-nozzle machine, each of those changes is a swap rather than a flush. At the five seconds both makers quote:
Half an hour of swapping on a print that already takes most of a day. That is the real change. Contours and rivers on a steep mountain go from impractical to merely slow.
Waste does not fall to zero. Snapmaker's own product page says the U1 still builds a small prime and wipe tower and clears each nozzle at the start, and its published test prints show 74–85% less total waste than a shared-nozzle printer, not 100%. Creality's K3 figures come from its own internal testing, published in a sponsored article, so treat them as a claim until independent reviews arrive.
Four is the number that matters
Both machines have four nozzles, and a map uses them up quickly: terrain, contour lines, water, and one more, such as woodland or a snow colour. A fifth colour sends you back to flushing a shared nozzle for that colour. For maps, plan around four.
Colour mixing is a different bet. Creality's SPARKX i8, shipping this autumn, blends its four filaments across layers to make intermediate tones rather than swapping nozzles. If it works as described, a gradient that changes with height is exactly what a relief map wants. But the claims are Creality's, the i8 still uses one shared nozzle, and I have not seen an independent test of the output, so I would wait for one.
What I would do
- On a single nozzle, don't put contours or rivers in a second colour on a mountain. Use one colour change at the snow line, which costs about 16 g, or print the water as separate pieces and inlay them.
- On a four-nozzle machine, terrain, contours, water and one more colour are finally reasonable. Budget an extra half hour, not an extra spool.
- Before buying for maps, count your colours. If they are four or fewer, a nozzle changer removes the problem. If they are more, it only makes it smaller.
You can check your own model the same way: export it from the map maker as 3MF, where each map layer is already a separate part, and look at how many of its print layers each colour touches.
Sources
Creality K3 pre-order announcement (sponsored, Creality's internal testing), Snapmaker U1 product page with its waste comparisons, and the SPARKX i8 launch.