Complete CNC Machining Process: How a Part Moves From Drawing to Shipped

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  What matters most
• 2
  Reading the Drawing and Running DFM
• 3
  Programming, Stock, and Fixture Planning
• 4
  Cutting Parameters by Material
• 5
  Holding ±0.005 mm and the Right Surface Finish
• 6
  Inspection, Documentation, and Shipping
• 7
  Step by step: from RFQ to shipped parts
• 8
  Which process fits the part

Every order starts with a file, not a machine. We open the 3D model and the 2D drawing together, then compare them feature by feature. What is the functional datum? Which surfaces actually mate with another part? Which tolerance is a real requirement and which one was copied from an old revision? That last question saves money more often than any toolpath trick.

The DFM pass looks for geometry the cutter cannot reach. A 3 mm end mill needs roughly 3 mm of clearance at the bottom of a pocket and about 1 mm at the corner radius. Deep pockets, sharp internal corners, and threads that stop against a shoulder all get flagged. If a wall is 0.8 mm thick on a 100 mm aluminium part, we will say so before cutting starts.

Tolerances get sorted by how they will be measured, not just by the number on the print. A ±0.005 mm bore needs a specific process: reaming, boring, or interpolation with a warm-up pass. A ±0.05 mm slot does not. Mixing those two in one operation is where shops lose time.

We also confirm material and finish at this stage. Aluminium 6061-T6, stainless 316L, 17-4PH, Ti-6Al-4V, POM, and PEEK all behave differently in the cut and in the fixture. Send the drawing and we return a quotation with free DFM analysis within 12 hours.

One more check belongs here: quantity. A single prototype and a 10,000-part run should not use the same setup plan. Prototype work favors fast fixtures and conservative cuts. Production work favors custom soft jaws, probing, and a stable cycle.

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  Send 3D plus 2DSTEP or IGES with a PDF drawing is the fastest combination.
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  Mark the datumsTell us which surface locates the part in your assembly.
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  State the finishRa 0.8–1.6 μm is standard; Ra 0.2–0.8 μm needs extra passes.

Programming is where the complete CNC machining process earns or loses its tolerance. The programmer picks the workholding first, because the fixture decides how many setups the part needs. On a three-axis machine a part with features on five faces may need four setups. On a simultaneous five-axis center the same part can often run in one or two.

Stock selection follows. We leave enough material to clean up the part without adding unnecessary passes. Too little stock and the part shifts or comes out undersize. Too much stock and the roughing pass takes twice as long, which shows up in the price. For aluminium plate we normally leave 0.5–1.0 mm on finished faces after roughing.

Toolpaths are ordered to keep the part rigid as long as possible. Roughing removes the bulk with the largest cutter the geometry allows. Semi-finishing brings the wall thickness close to nominal. Finishing runs last, often with a separate pass for the tight-tolerance features. On thin walls, a light finishing pass with a sharp tool beats a heavy cut every time.

Fixtures get designed around the datums from the drawing. Soft jaws machined in place, vacuum plates, and custom clamps all do the same job: hold the part without distorting it. A part that is clamped too hard will measure correctly on the machine and wrongly on the CMM after the vise opens.

For five-axis work we also check rotary clearance. The Ø400 mm rotary table has limits, and a long part swung at an angle can hit the trunnion. Simulation catches that before the spindle moves. Our 16 simultaneous five-axis machining centers cover travels from 500 × 500 × 450 mm up to 4,000 × 400 × 150 mm for long parts.

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  Fewer setups, tighter stack-upEach re-clamp adds positional error that no toolpath can remove.
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  Simulate before cuttingRotary clearance and tool-holder collisions are checked in the CAM file.
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  Fixture around datumsClamp on the surfaces the drawing already uses for location.

Cutting data is a starting point, not a rule. The numbers below are the windows we use for roughing and semi-finishing on a rigid setup, then we tune from the sound of the cut and the chip color. If a tool squeals, the feed is too low or the tool is too long.

Aluminium 6061-T6 cuts fast and clean. We typically run 3,000–12,000 rpm depending on tool diameter, with surface speeds around 300–500 m/min and 0.1–0.3 mm per tooth. 7075 is stronger and more abrasive, so we drop the surface speed slightly and keep the chip load up to avoid rubbing.

Stainless 304 and 316L work-harden. The cutter must keep moving. Surface speeds of 80–150 m/min with 0.05–0.15 mm per tooth work well, and every pass should cut below the hardened layer left by the previous tool. Dwelling in the cut is the fastest way to kill a carbide end mill in 316L.

Steel 4140 and 4340 sit in the middle: 120–200 m/min, 0.08–0.2 mm per tooth, with coolant or air blast depending on the operation. Tool steel and 17-4PH in the hardened condition need coated carbide and lower speeds. We check hardness before programming, because the same alloy name can arrive in two very different states.

Titanium Ti-6Al-4V and Inconel are the slow group. Surface speeds of 30–60 m/min, generous coolant, and no re-cutting of chips. These materials also move when you cut them, so we leave more stock for finishing and plan a stress-relief step on parts with tight flatness.

Plastics behave differently again. POM and PA need sharp tools and high spindle speed to avoid melting. PEEK is abrasive and expensive, so we plan the sequence to avoid scrapping a nearly finished part.

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  Match the insert to the jobAluminium-specific geometry for aluminium; coated grades for steel and stainless.
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  Keep the chip load upRubbing shortens tool life faster than a slightly heavy cut.
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  Watch the first partAdjust from measurement and sound, not from a table alone.

Tolerance and finish are two separate problems that often get solved in the same pass. Holding ±0.005 mm (±0.0002 in) means controlling three things: thermal growth, tool wear, and fixture repeatability. Miss any one and the part drifts during the run.

Thermal growth is the quiet one. A spindle running for an hour warms the machine and the part. For tight features we let the machine warm up, cut a test feature, measure it, and then apply the offset. On long runs we re-check the first part after 30 minutes to see whether anything moved.

Tool wear shows up as a slow trend, not a sudden jump. Probing or in-process measurement catches it. When a boring tool drifts 0.003 mm over 50 parts, the offset gets updated before the next batch rather than after a rejected lot.

Surface finish is planned, not hoped for. As-machined Ra 1.6–3.2 μm is normal for a clean finishing pass. Ra 0.8–1.6 μm needs a dedicated finishing pass with a sharp tool and a stable setup. Ra 0.2–0.8 μm usually means a finer step-over, a smaller tool, or a secondary operation such as polishing.

Deburring belongs in the process, not at the end. A 0.2 mm edge break on a machined edge prevents handling damage and makes the part safe to assemble. We deburr before inspection so the inspector sees the finished geometry.

Finally, finish and tolerance interact. A hardcoat anodize adds 20–50 μm of build-up per surface and can close a tight bore. If a bore is held at ±0.005 mm, mask it or finish it after coating. This is the kind of note that belongs in the DFM reply, not in a phone call after the parts arrive.

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  Warm up before tight cutsThermal drift is measured, not assumed.
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  Deburr before measuringBurrs hide true edges and can fail a go/no-go check.
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  Plan around coatingsAnodize and plating change dimensions by tens of microns.

Inspection runs through the whole job, not only at the end. We check raw material certificates when the stock arrives, monitor critical dimensions during the run, and perform a final inspection on 100% of parts before shipment. Reports are available on request, with the dimensions that matter to your assembly marked.

The measuring tools match the tolerance. Calipers and micrometers cover general dimensions. Bores at ±0.005 mm get checked with bore gauges or on the CMM. Surface finish gets verified with a profilometer when the drawing calls out Ra values.

Packaging protects the work that went into the part. Machined faces get separated, threads get protected, and parts ship in boxes that survive the trip. Confidential projects ship with the same handling as any other job, and we sign an NDA on request.

Timing is part of the process too. Quotation and DFM come back within 12 hours, production can start within 24 hours, and parts normally ship in 3–5 days. Those windows assume the drawing is released and the material is in stock. If a material has to be ordered, we say so in the quote instead of after the fact.

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  Raw material checkCertificates and hardness verified before cutting.
• 2
  In-process monitoringFirst-article and periodic checks on critical dimensions.
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  Final inspection100% of parts checked before they leave the floor.