Savannah CNC precision machining

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  What precision means in a machining quote
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  Why setup count controls accuracy
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  Which parts belong on a five-axis machine
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  How material choice changes the cut
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  How precision is verified before shipment
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  Setup choice by part geometry

Precision is not a single number. A drawing may show ±0.005 mm on one bore, a general tolerance block for everything else, and a surface callout of Ra 0.8–1.6 μm on a sealing face. Each of those has a different cost driver. The tight tolerance needs a stable setup and a temperature-stable machine. The general block needs a clean process plan. The finish callout needs the right tool path and a finishing pass, not just a slower feed.

When we quote Savannah CNC precision machining work, the first question is where the tolerance sits relative to the datum. A ±0.005 mm bore that references a face machined in the same setup is routine. The same bore referencing a face from a second operation adds stack-up, and that is where parts go out of spec. Setup count is usually the deciding factor, not spindle speed.

Surface finish and tolerance interact. A tool that leaves Ra 1.6–3.2 μm under normal cutting conditions can hold size well but will not seal against an O-ring. Pushing to Ra 0.2–0.8 μm usually means a separate finishing pass with a smaller stepover, which adds cycle time. Say which surfaces matter and which are cosmetic; the quote gets tighter and the part still works.

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  Tolerance is location-specificOne tight feature rarely means the whole part is tight.
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  Datum choice drives costFeatures cut in one setup are easier to hold than features split across two.
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  Finish is a separate operationRa 0.2–0.8 μm almost always adds a pass.

Every time a part leaves a fixture and comes back, two things happen. The part is re-located, and a small positioning error enters the stack. On a 3-axis machine, a part with features on four sides may need three or four setups. Each one adds a re-clamping step, and each re-clamp is a chance for chips or burrs to sit between the part and the fixture.

A 5-axis machine rotates the workpiece or the tool head, so the part can stay clamped while the tool reaches five sides. That single setup removes most of the re-location error. On parts with angled faces, deep pockets, or holes that must be true to each other, this is the difference between holding ±0.005 mm and chasing it.

The trade is not free. Five-axis motion needs more clearance planning, and tool holders get longer and less rigid in some orientations. For a simple plate with holes on one face, a 3-axis machine is faster and cheaper. Five-axis earns its place when the geometry has angles or when the tolerance crosses features that cannot share a fixture.

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  Each setup adds errorRe-clamping introduces positioning and chip-seating variance.
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  One setup, one datumFeatures cut together stay true to each other.
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  Rigidity still mattersLong tool reach can offset the gain on shallow simple parts.

A good candidate has features that point in different directions, or a tolerance that ties two of those features together. An angled mounting face with a dowel hole that must stay square to it is a classic case. So is a manifold with ports on several faces. On these parts, the alternative is multiple fixtures and a lot of inspection, which is slower and less repeatable.

A part with a single flat face, a few through holes, and a loose general tolerance does not need five axes. Sending it to a 5-axis center burns machine time without improving the result. We route those to a 3-axis or a mill-turn cell and keep the 5-axis capacity for work that uses it.

Size matters too. Our five-axis centers cover travels from 500 × 500 × 450 mm up to 4,000 × 400 × 150 mm, with a Ø400 mm rotary table on the compact machines. Long, slender parts often do better on a mill-turn center where the part turns and the tool follows, because the part is supported along its length instead of cantilevered.

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  Angled features → five axesHoles and faces that must stay true to an angled datum.
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  Flat and simple → three axesNo accuracy gain from extra rotary motion.
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  Long and slenderMill-turn supports the part instead of hanging it.

Aluminum 6061-T6 cuts fast and holds tolerance well, which is why it dominates prototypes and low-volume brackets. 7075 is stronger but more prone to distortion when a lot is removed from one side; roughing both sides before finishing helps. 2024 behaves similarly and machines cleanly if the tool path keeps heat down.

Stainless 304 and 316 work-harden. A light pass with a dull tool hardens the surface and the next pass cuts worse. The fix is a consistent feed that stays under the hardened layer, sharp tooling, and coolant where the geometry allows. 17-4PH machines better in the solution-treated condition and is often aged after machining.

Titanium Ti-6Al-4V and Inconel are slow on purpose. Cutting speeds drop, tool wear rises, and heat stays in the cut. These materials justify the tighter process control of a 5-axis setup because a re-clamp on a warped titanium part usually means scrap. Plastics such as POM and PEEK cut easily but move with temperature, so let the part stabilize before the final pass.

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  Aluminum6061-T6 is the default for fast, stable work.
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  StainlessKeep feeds under the work-hardened layer.
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  Titanium and InconelSlow speeds, high wear, tight process control.
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  PlasticsThermal movement shows up in the final dimensions.

Inspection starts before the cut. Incoming bar or plate is checked against the material certificate, because a substituted alloy will not hold the same dimensions after machining. In-process checks catch a drifting tool before a batch is finished. Final inspection measures the features on the drawing, not a sample of convenient ones.

For a ±0.005 mm callout, the measuring tool matters as much as the cut. A caliper is not the answer. We use micrometers, bore gauges, and CMM inspection depending on the feature, and reports are available on request. If your drawing calls for a first article report, say so at quote time so the inspection plan is built into the schedule.

Temperature affects measurement as much as machining. A part measured straight off the machine reads differently once it cools. On tight work we let the part stabilize before the final check. That is a small delay that prevents a much larger argument later.

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  Material firstA substituted alloy changes how the part moves.
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  Tool for the toleranceCalipers cannot verify ±0.005 mm.
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  Let it coolThermal growth shows up in the measurement.