Older foam simulators draw the cut as a ribbon — a thin surface that only hints at the shape. cncfoam.com instead models the foam as a true solid and computes the finished part with boolean (CSG) operations, so what you see is what you get.
The model
The pipeline is: build a watertight stock solid (your material block), build a solid cutter from the loaded profile (a prism for a straight cut, or a left-to-right loft for a morph), and run a boolean:
- 2/4-axis → intersect (keep the inside): the result is the part bounded by your profile — the thing you are cutting out.
- 3/5-axis rotation → subtract: each indexed pass removes material, and the stock rotates between passes.
The booleans run on a fast, robust manifold engine, so the result is always a clean, watertight solid that stays bounded by the foam block.
What the colours mean
- White/ghosted stock — the raw foam block before cutting.
- Green ghost — the loaded shape (the cut tool), so you can confirm size and position before you start.
- Yellow solid — the carved result: the actual part you will get.
The green preview honours your Object-bar offsets and scaling, so a skewed/offset cut shows as a skewed green shape — matching the carved yellow result.
Why it matters
A solid preview catches mistakes a ribbon hides: a profile that pokes out of the block, a morph that pinches, an indexed sequence that does not close up. You see the genuine 3D part, rotate around it, and check it before committing foam.
Performance
Booleans are heavy, so cncfoam.com computes the carve only when the geometry changes (load, resize, settings) — not every frame — and debounces rapid edits so dragging a slider stays responsive. Keep your sample resolution modest on very complex shapes for the snappiest carve.