Scan interval

The vertical line spacing on a filled engraving. The single biggest knob between speed and fill quality.

When a layer is set to Fill, the laser scans back and forth across the shape, firing on every horizontal line. The vertical distance between those lines is the scan interval.

Smaller interval → finer fill, darker (more lines per area), slower. Larger interval → coarser fill, lighter, faster.

The basics

A typical interval ranges from 0.05 mm (very fine, photographic) to 0.5 mm (coarse, fast). The right value depends on:

Beam spot size: your laser's effective dot at the work surface. Roughly your beam diameter. Below this, lines start overlapping and the interval no longer adds visual detail.
Material: wood and acrylic look different at the same interval. Anodized metals look acceptable at coarse intervals because the contrast is high.
Speed: slower speeds with the same interval engrave darker.

A rule of thumb: start at the beam spot size and adjust from there. If your spot is roughly 0.1 mm, start at 0.1 mm interval.

Equivalent in DPI

Interval and DPI are reciprocals:

DPI = 25.4 / interval_mm

So 0.1 mm interval is 254 DPI; 0.05 mm is 508 DPI; 0.2 mm is 127 DPI.

The Interval Test dialog shows both side by side.

How Beam Bench handles it

The Interval field lives on the Fill / Image layer settings, visible in the quick-edit strip of the Cuts/Layers panel and in the full layer editor.

The Interval Test is the way to find the right value for a new material, it sweeps a range of intervals at fixed power / speed and you pick the tightest one that still looks solid.

When it matters

Engraving photos and gradients: interval determines apparent resolution. Coarse intervals lose detail.
Engraving fills on cuts: coarser interval is fine; you are not viewing the result.
Time-to-burn budget: halving interval doubles burn time. Always check the Preview duration estimate.