Why do thin gaps get filled in during printing?

When a gap is narrower than one extrusion width, the slicer has two choices: skip it (leaving a gap) or fill it with a thin extrusion. Many slicers fill thin gaps to avoid weak spots, which eliminates the intended gap.

What is the minimum gap for a 0.4mm nozzle?

The practical minimum is 0.4mm (one nozzle width). Gaps of 0.5-0.6mm print more reliably. Anything under 0.4mm will likely be filled by the slicer or leave an inconsistent channel.

How do slicer settings affect gaps?

Enable "Detect thin walls" and adjust "Thin wall minimum width" in your slicer. Some slicers have "Gap fill" settings that control whether narrow spaces are filled. Reducing line width can help print slightly narrower gaps.

Does gap width affect part strength?

Narrow gaps between walls create weak points because there is less material connecting the two sides. If structural integrity matters, ensure gaps are clearly wider than the nozzle so the slicer creates clean separate walls.

3DPrintCalcs

Wall Gap Calculator — Minimum Resolvable Gap

Find the minimum gap between parallel walls that your printer can resolve.

Nozzle Diameter

Line Width

Usually 100-120% of nozzle diameter

Wall Count (per side)

Desired Gap

How We Calculate This

Wall Gap Formulas

Min printable gap = Nozzle diameter (cannot create gap smaller than nozzle)
Min visible gap = Line width x 0.5
Wall thickness = Wall count x Line width

The slicer generates toolpaths based on line width. Any gap narrower than one line width cannot accommodate a full extrusion path, so it will either be skipped or filled with a thin gap-fill extrusion.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify settings with test prints before committing to final prints.