What Multi-Colour 3D Printing Really Costs

When people see our price list, the first question is usually why a keychain with eight colours costs more than one with two. The plastic is almost the same. The difference is time, and it comes from one specific thing a multi-colour printer has to do over and over: change colour. Here is what that costs, measured on real prints from our shop.

How a multi-colour print is made

A 3D printer builds an object one thin layer at a time, so even a 3 mm coin is a couple of dozen layers. It prints one colour at a time. When a layer needs a second colour, the printer has to stop, unload the first colour, load the next one, and push out a little plastic to flush the old colour out before it continues. That cycle is a colour change, and on a layer with four colours it happens three times.

The changes happen automatically, so nobody has to swap colours by hand, but they are not free.

What one colour change costs, measured

We timed changes on our own prints. Each one takes the better part of a minute, and flushing the old colour out uses a little plastic that goes in the bin. Neither sounds like much. Multiply them by the number of changes a design needs and they add up quickly.

The coin with a raised word is a good example: its 21 changes alone take about a third of the whole print time, and the plastic they flush out is close to half the weight of the coin itself.

Why the same picture can take 49 minutes or 73

The last three rows are the same 70 mm coin with the same four colours. The only difference is how the colours sit in the plastic, and it changes the print time by 24 minutes.

In a flush or raised print, the colours sit side by side in the same layers. Every layer that contains all four colours needs three changes, and that repeats for every layer of the coloured part, which adds up to 18 or 19 changes.

In a stepped print, each colour is a terrace one step above the last. That means each layer only contains one colour, so the printer changes colour once per terrace instead of several times per layer: three changes for four colours. The trade-off is the look. Stepped prints have a layered, papercut feel, while flush prints are smooth like a coin. Neither is better; they are different.

What doesn't change the price much

• Plastic. The plastic in a keychain costs very little, even counting what's flushed out at each colour change.
• Font choice. A fancy font uses about the same plastic as a plain one. It only matters if its strokes are so thin they need to be bigger to print at all.
• Quantity. Identical pieces cost the same each, because each is printed from the same file. Several pieces share one mailer, so shipping hardly changes.

How to keep a design affordable

1. Use fewer colours. Two or three colours read better at keychain size anyway. Dropping from five colours to three removes two changes from every layer that had all five.
2. Try stepped for colourful pictures. If a picture has many colours, the stepped style can cut the changes dramatically, as the table shows.
3. Keep colours on the same layers. A raised name with a flush background needs fewer layers with several colours than a design where colours are scattered through the whole height.
4. Size it sensibly. Bigger prints take longer to lay down, layer after layer. The size tiers on our pricing page show where the steps are.

How our prices use these numbers

Every product has three sizes with a fixed price for designs that fit, and those prices already include a typical number of colour changes. If a design needs far more changes than its size covers (an eight-colour photo on a small keychain, say), the designer prices it exactly from the slice, including every change, and tells you why. You always see the exact price before paying, and you can try a different style or fewer colours to bring it down.