Reno CNC machining the precise parts for your business

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  Reno CNC machining: what actually sets the accuracy of a part
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  3-axis, 4-axis or 5-axis: which one your part needs
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  How material choice changes the cutting strategy
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  When Reno CNC machining is the wrong process
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  How the shop proves the part is correct
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  Matching part features to the right process

A CNC machine does not create accuracy. It reproduces the geometry the CAM program tells it to follow, and the error budget comes from somewhere else. The largest contributors are thermal growth in the spindle and ballscrew, tool deflection under cutting load, workholding stiffness, and the resolution of the control loop. A machine quoted at ±0.005 mm can hold that figure only when the part, the fixture and the tool path cooperate.

Thermal drift is the quiet one. A spindle running at 12,000 rpm for two hours grows a few micrometres in Z, and that shift lands directly on your depth tolerance. Shops that hold tight numbers warm up spindles before the first cut and keep the floor temperature stable. If your drawing calls for ±0.005 mm on a bore depth, ask how the shop controls thermal drift. The answer tells you more than the machine list.

Tool deflection scales with the cube of the length-to-diameter ratio. A Ø6 mm end mill hanging 60 mm out of the holder will bend far more than the same tool at 25 mm. On thin ribs and deep pockets, this shows up as taper in the wall and chatter marks on the floor. Short, stubby tools and a rigid holder fix more tolerance problems than a slower feed rate does.

Workholding closes the loop. A part clamped on four points of a thin flange will spring when the vise releases, and the measured dimension changes after unclamping. For thin-walled parts, we plan the fixture before the tool path, and sometimes machine the fixture itself on the same machine.

Axis count is a setup decision, not a quality badge. A 3-axis machine cuts a part from one direction. If your part has features on five faces, a 3-axis route means four or five separate setups, each one adding a re-fixturing error. A 5-axis machine reaches those faces in one setup, so the datums never move. That is where the accuracy gain comes from, not from the extra axes themselves.

Simultaneous 5-axis is a different animal from 3+2 positioning. In 3+2, the table tilts to an angle and locks, then cuts like a 3-axis job. In simultaneous mode, all axes move together to keep the tool normal to a curved surface. Impellers, bladed disks and contoured medical housings need simultaneous motion. Prismatic brackets and plates do not, and forcing them onto a 5-axis machine only raises the hourly rate.

Mill-turn centers handle parts that would otherwise need two machines. A shaft with a milled flat, a cross-drilled hole and a turned journal can be finished in one cycle. The gain is concentricity: the turned diameter and the milled feature share one spindle, so runout stays inside ±0.01 mm without a second op. For parts under Ø400 mm, a mill-turn center with a rotary table is often the cheapest path to tight concentricity.

Size drives the choice too. Our largest travel is 4,000 × 400 × 150 mm, which covers long extrusion profiles and rails. Medium frames run 750 × 1,150 × 550 mm or 600 × 600 × 600 mm. Small precision work sits on 500 × 500 × 450 mm or 500 × 310 × 200 mm machines, where the smaller envelope gives better thermal stability and faster acceleration.

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  One setup beats four5-axis removes re-fixturing error on multi-face parts.
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  3+2 is not simultaneousPositioned cutting is cheaper and fine for prismatic work.
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  Mill-turn for concentricityOne spindle keeps turned and milled features aligned.
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  Match envelope to partSmall machines hold small parts better.

Aluminium 6061-T6 cuts fast and holds ±0.005 mm easily on rigid setups. It also moves with heat, so a part with a 300 mm span can grow 0.007 mm over a 10 °C shop swing. For long aluminium parts with tight hole spacing, we rough, let the part cool, then finish. 7075 gives higher strength but is more notch-sensitive and tends to chip at sharp internal corners; a small corner radius helps.

Stainless 304 and 316 work-harden. If the tool rubs instead of cutting, the surface gets harder and the next pass breaks the edge. The fix is a positive rake insert, constant feed, and no dwell in the cut. 17-4PH (SUS630) in the H900 condition machines cleanly and is common for medical and aerospace shafts. 316L stays the default for anything that touches aggressive fluids.

Titanium TC4 (Ti-6Al-4V) conducts heat poorly, so the cutting edge absorbs it. Speeds drop to roughly a quarter of aluminium, and coolant must reach the tip under pressure. Inconel is worse and often justifies ceramic or carbide tooling with high-pressure through-spindle coolant. These materials are not the place to save on cycle time; a broken tool in a titanium pocket costs far more than the extra minutes.

Plastics behave differently again. POM and PEEK machine to tight tolerance but hold internal stress, so a thick section can bow after the skin is removed. ABS and PC are softer and tend to burr at the exit edge. Carbon fibre is abrasive and eats tool edges, so we schedule fresh tools for it and control dust at the machine.

CNC machining is a subtractive process with a fixed setup cost. For a single prototype, that cost is spread over one part and the unit price looks high, but the part arrives in days and matches the drawing. For 10,000 identical simple parts, die casting or injection molding will beat it on unit price once the tooling is amortized. The crossover usually sits somewhere between a few hundred and a few thousand units, and it depends on geometry.

Deep features are a limit. A pocket deeper than about four times its width needs a long, thin tool, and that tool deflects. We can reach further with EDM or by flipping the part, but both add cost. If your design has a 3 mm wide slot that is 40 mm deep, expect to pay for it. Redesigning the slot to a wider, shallower form often cuts the price more than any negotiation.

Thin walls are another boundary. Below roughly 0.5 mm in aluminium, the wall deflects under clamping and cutting force, and chatter becomes hard to avoid. The part may measure correctly on the machine and spring out of tolerance after unclamping. Support structures, sacrificial tabs and light finishing passes help, but there is a floor below which the process stops being repeatable.

Finally, surface finish and tolerance fight each other on cost. Ra 0.8–1.6 μm is a normal machined finish. Ra 0.2–0.8 μm needs slower finishing passes, sharper tools and often a separate operation. If the drawing only needs Ra 1.6–3.2 μm, say so; over-specifying finish is one of the most common ways engineers add cost without adding function.

A tolerance is only as good as the measurement behind it. Calipers read to 0.02 mm on a good day, and they depend on the operator's hand. For anything inside ±0.05 mm, a CMM or a micrometer with a known-zero standard is the right instrument. GreatLight inspects 100% of parts before shipment, combining raw material checks, in-process monitoring and a final inspection, with reports available on request.

In-process checks catch drift before the last part is cut. On a 500-piece run, we measure the first article, then sample at intervals. If the trend moves toward the limit, the operator adjusts the offset before any part crosses it. This is cheaper than sorting a finished batch, and it is why the qualification rate holds at 99.99%.

The drawing matters as much as the gauge. A tolerance applied to a non-functional surface wastes money. A datum that does not match how the part sits in the assembly causes arguments at incoming inspection. We flag these during the free DFM analysis, which goes back with the quote within 12 hours, so the questions get answered before metal is cut.

Certifications add a paper trail on top of the measurement. Our quality system is registered to ISO 9001:2015, IATF 16949:2016 for automotive, ISO 13485:2016 for medical devices, and ISO 27001:2022 for information security. Those registrations cover the process, not any single part; the inspection report is what proves the part you receive.