Single-nozzle multi-colour printing works by throwing plastic away. To change from red to blue, the machine pushes blue through the hotend until no red comes out, and everything that comes out in between is scrap. That is the entire mechanism, and understanding it is the difference between multi-colour being a delight and being a slow way to convert filament into bin contents.
The Kobra 3 is built around a four-spool feeder, so this is the page to be blunt about it.
A four-colour job, costed
A small model with four colour changes per layer: 60 g of finished object, and 200 g of filament off the spool. Five hours, $24/kg:
| Term | Amount |
|---|---|
| Filament, all 200 g of it | $4.80 |
| Electricity, 0.5 kWh | $0.09 |
| Machine time at 30 cents/hour | $1.50 |
| 6% failure allowance | $0.41 |
| Total | $6.80 |
Seven-tenths of the plastic you paid for is in the waste bin. Priced against the finished object, the effective filament cost is more than three times the spool price, and no amount of shopping for cheaper filament fixes that — the fix is fewer colour changes.
Put your own model mass plus your own weighed purge into the cost calculator. The single most useful thing you can do on a multi-material machine is weigh one purge tower and stop guessing.
How to spend less of it
The purge scales with the number of colour changes, not the number of colours:
- Group by colour in the model. A design where each colour appears in one contiguous band costs a fraction of one where all four appear on every layer.
- Print several copies at once. The purge per layer is roughly fixed, so four copies of a model on one plate share it.
- Use the purge. Some slicers can extrude the flush into infill or into a second object rather than a tower.
- Accept fewer colours. Two colours is not half the waste of four; it is much less than half.
The wattage behind the nine cents above is an estimate from comparable machines rather than a metered figure, which the specifications record honestly. It is also the least important line in the table by a wide margin.
The printer underneath the feeder
Strip away the colour system and this is a competent 250 mm bed-slinger with a 300 °C hotend, automatic levelling and a direct-drive extruder. That hotend ceiling is a real step up from the 260 °C machines earlier in the same family: filled PETG and filled PLA come into range, and PETG gets comfortable headroom rather than sitting at the top of its window.
The plate is 250 mm, which is a genuinely useful size — large enough for most single parts, small enough to reach temperature quickly and to keep the running cost modest.
There is no enclosure, so ABS and ASA remain out of reach in any meaningful size, and the stock nozzle is brass, so a hardened one is the first purchase if filled filament is on your list.
Failure modes the colour system introduces
Multi-material hardware adds failure modes a plain printer does not have, and they are worth knowing before your first long colour job:
- A filament that will not retract cleanly jams the change and stalls the print — this is why wet or badly wound spools cause more trouble here than on a single-colour machine, and why tangled filament is suddenly a four-times-more-likely event.
- Colour bleed when the purge is set too short: the new colour arrives contaminated. That shows up as colour change bleeding, and the fix costs filament, which is the trade at the heart of the whole system.
- A toppled purge tower takes the print with it, and a tall tower on a small footprint is exactly what a many-change model produces.
When to skip the colour system entirely
If colour is not why you are buying, buy the machine without the feeder and save both the purchase and the waste. If you want multi-colour and engineering materials, this is the wrong shape of machine — an enclosed multi-material printer like the Creality K2 Plus is the class that does both. And if you want colour on large models, do the purge arithmetic before you commit; at that scale the waste can exceed the cost of a second printer over a year.