A support block under a 40 mm square overhang standing 30 mm off the plate, at 15% density with no perimeters, takes 25 minutes. Raise the density to 25% and it becomes 36 minutes.
That is machine time for a single overhang. A part with several will carry several of those.
Density is the lever, and the default is usually too high
Support density is not doing structural work. It only has to hold up the first bridged layer over it, which means it can be far sparser than most slicers ship it.
Going from 25% to 15% takes eleven minutes off this one block, and it makes the supports easier to snap off rather than harder — the two benefits point the same way, which is unusual.
The time that is not on the machine
Removal. Snapping, cutting and scraping supports off a part, then sanding the marks they left, is hands-on human time, and on an awkward part it exceeds the print time the supports took.
That inverts the usual costing logic. Machine time is cheap and unattended; your time is neither. A part that takes an extra half hour to print but needs no cleanup is comfortably the better outcome.
Reorientation usually beats optimisation
Before tuning support settings, try turning the part. Tipping a bracket onto its back, standing a shell on its open face, or splitting a part in two and gluing it can remove every support in the job.
The cost of that is layer direction: layers bond weakly in Z, so an orientation chosen for printability may be an orientation that fails under load. That trade is worth making deliberately rather than accepting whatever the slicer generates.
Two structural risks supports carry
- They are the thing a nozzle catches. A tall, thin, sparse tower is exactly the geometry that gets knocked loose, and it takes the print with it.
- They fuse to the part when they are too dense or too close. That converts a five-minute cleanup into a scrapped part, and it is the failure mode a lower density prevents.
Treat a support block as a zero-wall prism and time it in the print time estimator. The supports guide covers interface layers, overhang angles and the settings that decide how easily the block comes off.