Skip to content
Sendot Technology

CNC Machining Process: From 3D Model to Finished Metal Part

Sendot Engineering Team· Custom ManufacturingJuly 28, 2026

This is the CNC machining process in action — a 3D CAD model becoming a finished metal part, one cut at a time, as the tool removes material from a solid block until the geometry on the drawing appears in metal. It is how custom parts are made subtractively: the design is programmed into toolpaths, and each pass leaves the part closer to final. See our CNC machining services and send your CAD file for a fast quote.

▶ Watch this video on Facebook

Key takeaways

  • From model to metal: a 3D CAD model is turned into machine toolpaths, then cut into a solid metal blank — subtractive manufacturing, where material is removed rather than added.
  • Roughing then finishing: heavy passes remove the bulk quickly, then light finishing passes leave the final surface and hold the tolerance — which is why the part looks rougher early and clean at the end.
  • Tolerance & finish: Sendot holds ±0.05 mm on critical features and surface finish to Ra 0.2 µm where a drawing calls for it.
  • 30+ materials — aluminium, alloy & stainless steel, brass, titanium and engineering plastics.
  • No MOQ — one prototype or a low-volume run; CNC samples in 3–5 working days, quote within 12 hours of receiving CAD.

How a 3D model becomes a machined part

Subtractive machining works in the opposite direction to 3D printing: instead of building a part up, it starts with a solid block and removes everything that is not the part. The sequence in the video is the same one every machined part follows.

  1. CAD model: the part is designed as a 3D solid — the single source of truth for the geometry.
  2. CAM programming: the model is converted into toolpaths — the exact routes, speeds and tools the machine will use.
  3. Workholding: a blank of the right material is clamped so it stays rigid while it is cut.
  4. Roughing: large, fast passes clear away the bulk of the material, leaving a little stock on every surface.
  5. Finishing: light, precise passes bring the part to final size and surface finish — this is where tolerance is held.
  6. Inspection: critical dimensions are checked, on request with a CMM report and material certificate.

What we machine this way

  • Custom metal parts — housings, brackets, shafts, plates, fixtures and complex geometry
  • Materials: aluminium, alloy & stainless steel, brass, titanium, engineering plastics — 30+ in total
  • Tolerance: ±0.05 mm on critical features; CMM inspection and FAI reports on request
  • Files: 3D STEP preferred; also IGES, X_T, DWG, PDF, STL

Frequently asked questions

What is the CNC machining process, in short?
CNC machining is a subtractive process: a computer-controlled machine removes material from a solid block with cutting tools until the part matches its 3D model. The model is turned into toolpaths, the blank is clamped, then roughing passes remove the bulk and finishing passes bring the part to final size and surface finish. It suits precise metal and plastic parts from one prototype to low-volume production.
How is a 3D drawing turned into a machined part?
The 3D CAD model is imported into CAM software, which generates the toolpaths — the routes, tools, speeds and feeds the machine follows. Those instructions drive the CNC machine to cut a clamped blank. A 2D drawing is added to communicate which dimensions are critical and what finish is needed, so the shop machines to the right tolerances rather than guessing.
Why does the part look rough at first and smooth at the end?
Because machining runs in two stages. Roughing uses heavy, fast passes to remove material quickly and leaves visible tool marks and a little extra stock. Finishing then takes light, slow passes over that stock, which produces the clean surface and holds the final tolerance. The transformation you see in the video is roughing giving way to finishing.
What tolerance and surface finish can you achieve?
Sendot holds ±0.05 mm on critical features, with tighter control on specific dimensions confirmed at quotation, and surface finish to Ra 0.2 µm where a drawing requires it. Not every feature needs to be tight — tolerancing only what fits or seals keeps cost down, and we flag this in a free DFM review with every quote.
Is there a minimum order to have a part machined?
No. Sendot has no minimum order quantity on CNC machining — a single prototype is a valid order, and the same process scales to low-volume production. CNC samples typically run 3–5 working days, and you get a quote within 12 hours of sending your CAD file.

Get your part machined

Have a 3D model you want to see turned into a finished metal part? Upload your CAD file on our Request a Quote page. Our engineers return a DFM review and price within 12 hours, with global shipping from a single prototype to low-volume production.

Related manufacturing services

Explore how Sendot Technology can manufacture your custom parts:

Related videos

+86 15818870852LUKE@sendottech.com+86 15818870852