Why do fine details disappear or come out wrong? Minimum detail size vs bit geometry

The three physical limits

1. A round tool can't enter a gap smaller than itself. Every feature narrower than the end mill simply does not happen (skipped silently or flagged; see the tool-won't-fit entry). Inside corners always get the tool's radius.
2. A V-bit renders width as depth. A 0.01 inch wide line with a 90 degree bit carves only 0.005 inch deep, which is nearly invisible. Fine V-carved detail needs enough WIDTH to gain visible depth, or a steeper (narrower angle) bit. A 60 or 30 degree bit gains depth faster for the same width, at the cost of fragility.
3. Wood has grain. A standing ridge or island that is very thin across the grain will likely chip out no matter what the toolpath says. The preview does not know about fibers.

Practical starting points (rules of thumb for wood, test on scrap)

These are starting points to test on scrap, not software limits:

• Pocketed or profiled detail: the smallest gap must be at least the detail-tool diameter plus a little. Plan a detail pass with a 1/16 or 1/8 inch tool where the design is tight.
• V-carved line work: strokes of about 1 mm or wider tend to read clearly. Below that, try a narrower-angle bit or an engraving bit at a fixed depth.
• Standing (raised) detail: make it about 1.5 to 2 mm thick or more, and thicker across the grain.
• 3D relief surface detail: limited by tip radius AND stepover AND model resolution. The coarsest of the three wins (see the ridges and jagged-edges entries).

How to check BEFORE cutting

1. Preview at high quality and LOOK at the fine areas. What is missing there is missing in wood.
2. Measure the tightest gap (Measure tool) against the planned bit.
3. When detail loses, try these in order: scale the design up, simplify it, switch to a finer bit or a narrower-angle V-bit, or move that detail to a laser (see the laser entries).

Pro tips

• Doubling the size of a struggling design solves more problems than any bit change. Detail difficulty rises sharply for small letter heights.
• "The preview shows it but the wood chipped it" is limit 3 (grain). The software was honest; the material vetoed it.