Automatic CNC Machining for Production Parts

In automatic CNC machining the machine executes a stored program with no operator input at the cut. The operator loads the stock, closes the door, presses cycle start, and the control runs the tool changes, feed moves, spindle speeds and coolant on its own. On a lathe with a bar feeder, or a mill with a pallet changer, the machine can load the next blank too.

That is different from manual or semi-manual work, where an operator turns handwheels, indexes a rotary table by hand, or measures with the spindle stopped. Once the program is proven and the offsets are set, the cycle repeats without anyone touching the machine. The first part proves the setup. Every part after that follows the same path.

The distinction matters for quoting. A job that runs unattended needs a stable setup, reliable tool life and a way to catch a broken tool before it scraps the rest of the batch. If any of those three is missing, the part is better cut manually for now.

The program is only one part of it. Workholding decides whether the cycle can repeat. A vise with a hard stop, a dedicated soft jaw, or a fixture with dowel pins gives the blank the same position every load. If the operator has to tap a part against a stop by feel, the position moves and so do the dimensions.

Tool life is the second variable. We log tool changes by cycle count and check wear on a schedule. A 6 mm end mill cutting 7075 aluminium at 12,000 rpm may hold size for hundreds of parts. The same cutter in 17-4PH stainless is a different story, and the program needs a tool breakage check or a spindle load limit.

Offsets need a plan too. Thermal growth, tool wear and fixture settle all shift the zero point over a long run. We either schedule a probe cycle to re-set work offsets, or hold a sample part every few hours and adjust. Which one we use depends on the tolerance band and the feature that is most likely to drift.

Automatic runs hold ±0.005 mm (±0.0002 in) on critical features when the setup is right. That is not a claim about every dimension on every part. It applies to the features the drawing calls out, measured on a CMM or a vision system with a stable thermal environment.

Surface finish follows the tool path. As-machined surfaces land at Ra 1.6–3.2 μm. A high-finish cut on a dedicated finishing tool gets Ra 0.8–1.6 μm. Fine finishing, usually on a lathe or after a separate pass, reaches Ra 0.2–0.8 μm. Facing marks, scallop height and step-over distance all show up on the surface, so the finish call-out should match the function.

Part size sets the machine. Our largest travel is 4,000 × 400 × 150 mm. Medium work runs on 750 × 1,150 × 550 mm or 600 × 600 × 600 mm platforms. Compact parts, especially high-volume ones, go on 500 × 500 × 450 mm or 500 × 310 × 200 mm machines, often with a Ø400 mm rotary table so the part can be cut on several faces in one cycle.

• 1
  Aluminium6061, 7075, 2024, 5052, 6082 and ADC12 cut fast and hold size well.
• 2
  Stainless303 and 316L machine cleanly; 17-4PH needs slower feeds and more tool changes.
• 3
  Titanium and InconelCut on rigid setups with heavy coolant; cycle times and tool wear rise sharply.
• 4
  PlasticsPOM, PEEK and ABS need sharp tooling and air blast, not flood coolant.

Every part is inspected before shipment, but inspection alone does not keep a run in band. What does is a sampling plan tied to the feature that drifts first. For a turned shaft, that is often the diameter nearest the chuck. For a milled housing, it is the bore with the longest tool reach.

Raw material is checked on arrival for grade and hardness. In-process checks run at a set interval, and the operator records the reading on the traveler. If a reading moves toward the limit, the offset is adjusted before the next part, not after the batch. Final inspection confirms the last parts match the first.

Inspection reports go out on request. For regulated work, the report can include the CMM program name, the datum scheme and the measured values, so a quality engineer can trace each number back to a drawing call-out.

Automatic cycles often leave sharp edges and witness marks that a drawing does not allow. We deburr in-house, then move parts to the finish that matches the function: anodizing for wear and corrosion, electroless nickel for uniform coverage on complex shapes, bead blasting for a matte look, or laser marking for traceability.

Laser marking holds a minimum character height of 1.5 mm. Below that, the mark is hard to read after anodizing and may not survive handling. If a part number has to be legible for ten years, plan the mark into the drawing rather than adding it later.

For assemblies, we can run the machining, finishing and light sub-assembly under one purchase order. That removes a shipping step and keeps the traceability chain inside one quality system.