Differences between CNC machining and 3D printing

CNC milling cuts a shape out of solid stock. FDM printing melts filament and stacks layers. Both make prototypes. They do not automatically deliver the same strength or the same tolerance.

A milled part is the alloy you chose, through the section. A printed part depends on infill, walls and layer direction. A tensile load between layers can split sooner than the same shape milled from bar. That does not make printing useless. Fit checks, ergonomic models and many fixtures are reasonable FDM jobs.

Milling can hold a tighter band when workholding and tools allow it. We still do not promise microns on every file. FDM warp, shrink and the first layer move dimensions. If you need a tight tolerance, expect review.

Milling wants STEP. A slicer wants a mesh, usually STL. See STEP and STL.

Milling cost grows with the blank and the removed volume. Printing cost grows with filament and print time. Without a slicer result we do not invent the hours. Prototype methods outlines the choice.