For a 50 mm square tower carried solid to a 60 mm print height: 150,000 mm³, which is 186 g of PLA. That is $4.09 of plastic and 6.1 hours of machine time thrown away, against a total print cost of $6.03 for the tower alone.
On most multi-colour prints the tower weighs more than the model.
Why it is that large
The tower exists to flush the old colour out of the melt zone. A hotend holds a few tens of cubic millimetres of molten plastic and does not swap it cleanly, so every tool change pushes a purge volume through and parks it somewhere that is not your part.
The total is therefore driven by number of tool changes, not by how much of each colour the model uses. A four-colour print that alternates on every layer purges four times per layer for the whole height, whether the coloured feature is a logo or the entire object.
The three things that actually reduce it
- Fewer colour changes per layer. Grouping colours by height rather than scattering them cuts the change count directly, and the change count is the whole equation.
- A shorter tower. If the multi-colour region ends at 20 mm, the tower does not need to continue to 60 mm. Most slicers will let you cap it.
- Purging into infill or into a sacrificial object. The waste still happens, but it lands inside the part or inside something useful instead of a solid block.
What it means for costing a multi-colour job
Price the tower as a part. It has a mass, it has a print time, and both belong on the invoice — a 186 g tower next to a 60 g model means the job consumes almost 250 g of filament while you are quoting on 60.
The failure exposure is worth noting too: a tall thin tower is exactly the geometry a nozzle knocks over, and if it goes, the print goes with it.
Estimate your own tower by entering its footprint and height in the print time estimator, then cost it in the print cost calculator.