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Staircase lines in fiber laser relief engraving: slicing vs depth maps

Short answer: visible steps in a fiber laser relief usually come from how depth is encoded before the laser ever fires. Grayscale depth maps turn a smooth surface into a limited number of gray levels, and each level becomes a band of equal depth. Slicing the 3D model directly makes each layer follow the model's true outline at that height, and you choose how fine those layers are.

The problem

You engrave a relief — a coin, a medallion, a sculpted logo — and the curved surfaces come out as terraces or contour rings instead of smooth slopes. The steepest areas look fine; gentle slopes show the worst banding.

Why it happens

Most galvo software marks depth from a grayscale depth map: a 2D image in which brightness stands for height. The software converts gray levels into passes or power, so the result can only be as smooth as:

  • the number of gray levels the map carries and the software actually uses,
  • the image resolution — a pixel grid laid over curved outlines, so edges of each level are stair-cased in plan view too,
  • how the map was made — a map rendered from a 3D model has already thrown away the exact geometry.

Gentle slopes suffer most: a small change in height spreads one gray level over a wide area, which marks as a flat band with a sharp edge.

How slicing is different

A 3D Slice action in FocuZ imports the model itself — STEP, STL, OBJ or 3MF — and cuts it into horizontal layers. Each layer is filled inside the model's exact cross-section at that height, as vector geometry, so the outline of every layer is where the model says it is, not where a pixel grid rounds it to.

What that gives you:

  • Outlines at true resolution. Layer boundaries are vector paths, not pixel edges.
  • Control over step size. Depth still builds up layer by layer, so a slice is still a small step — but you set the slice count, and finer slices make smaller steps. You are not limited to the levels a depth map happened to contain.
  • The model stays editable. Scale, rotate and place the model in FocuZ; the slices are recomputed from the geometry, not from a re-rendered image.

Getting smooth results

  1. Start from a good model. A STEP solid needs no watertight checks; an STL needs enough polygons to avoid micro-faceting on curves.
  2. Measure your material removal rate, then set the slices from it. One pass rarely removes enough to measure accurately, so run a test area with your settings for many passes (say 50 or 100), measure the depth, and divide it by the number of passes. That's your depth per pass. For example, 0.50 mm deep after 50 passes is 0.01 mm per pass. With one pass per slice, set Slices/mm to 1 ÷ that depth — 100 in the example — and FocuZ sets the # of Slices to match the model's height. More, thinner slices give smoother slopes.
  3. Turn the fill between slices with Auto Rotate (and a Step angle), so line patterns don't stack into ridges.

See it for yourself

The free Slice vs Depthmap comparison tool loads a 3D model and shows the same surface as depth-map levels and as true slices side by side.