Karatech CNC Precision Machining: How Tight Tolerances Are Actually Held

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  What Karatech CNC precision machining controls on the shop floor
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  When 5-axis machining is the only practical route
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  How material choice shifts the tolerance window
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  Surface finish, inspection and what the report proves
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  From prototype to 10,000 parts without a process reset
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  Matching the process to the part

Precision machining removes material until a part matches the drawing. The hard part is not cutting metal. It is holding the relationship between features while the material moves. Every cut releases internal stress, and every clamp pushes the part slightly out of shape. A tolerance of ±0.005 mm is therefore not a machine spec. It is the result of a stable setup, a sharp tool and a temperature the part can live with.

Three things decide whether that tolerance is reachable. First, the feature must be cut in one setup whenever possible. Second, the tool has to be rigid enough that deflection stays under a fraction of the tolerance band. Third, the datum scheme on the drawing has to match the way the part is actually held. When those three line up, ±0.005 mm is routine on our 5-axis centers. When they do not, no amount of inspection saves the run.

Karatech runs 127 high-precision CNC machines across three plants, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. That mix matters because it lets us pick the machine that fits the geometry instead of forcing every part onto one platform. A 4,000 mm rail and a Ø30 mm medical fitting do not belong on the same machine.

The practical meaning for a design engineer is simple. Send the drawing with datums, material condition and any functional surfaces marked. We return a DFM analysis within 12 hours that says which features are safe, which are tight and which need a design change before quoting.

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  One setup beats threeFewer re-clamps means fewer stacked errors.
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  Rigidity sets the floorLong tools and thin walls push the achievable tolerance up.
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  Datums must match fixturingA drawing datum that cannot be touched in the vise is a problem.

A 3-axis machine moves the tool in X, Y and Z while the part stays still. That works well for prismatic parts with features on one or two faces. Once a part has angled holes, contoured pockets on multiple faces or undercut surfaces, the setup count climbs fast. Each extra setup adds a re-clamp, a new datum and another chance to lose position.

Simultaneous 5-axis machining solves this by tilting the tool or the table while cutting. A port with a compound angle, an impeller blade or a deep cavity with draft can be finished in one continuous pass instead of five interrupted ones. The gain is not speed. It is positional consistency between features that must line up after assembly.

The trade-off is programming time and fixturing cost. Five-axis work needs a posted toolpath that accounts for tool holder clearance, and it usually needs a dedicated soft jaw or a custom fixture. For a one-off bracket with two holes, that is not worth it. For a manifold with nine intersecting bores, it is the only sane choice.

We keep 16 simultaneous 5-axis centers and a Ø400 mm rotary table for this class of work. Parts up to 4,000 mm can be handled on the large-travel machines, while most 5-axis jobs sit in the 500 × 500 × 450 mm envelope.

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  Use 5-axis forCompound angles, contoured faces, deep undercuts, impellers.
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  Stay 3-axis forFlat plates, simple housings, features on two faces.
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  Watch clearanceThe tool holder, not the cutter, often limits access.

Aluminium 6061-T6 cuts clean and holds ±0.005 mm without drama on a rigid setup. Its thermal expansion is roughly 23 μm per meter per °C, so a 300 mm part that warms 5 °C during roughing grows about 35 μm. That is already seven times the tolerance band. We rough, let the part rest, then finish. Skipping the rest is the most common cause of a part that measures well in the machine and fails on the CMM.

Stainless 304 and 316 work-harden. A dull insert rubs instead of cutting, the surface hardens, and the next pass deflects. Tool changes get scheduled tighter on these grades. 17-4PH in the H900 condition machines closer to alloy steel than to 304, and it is often the better choice for a shaft that needs both corrosion resistance and strength.

Titanium TC4 (Ti-6Al-4V) and Inconel sit at the other end. Low thermal conductivity pushes heat into the cutting edge, so speeds drop and tool life shortens. Thin walls on these alloys need light radial passes and generous support. We quote them with a longer cycle and a higher scrap allowance, not a different tolerance.

Plastics behave differently again. POM and PEEK move with temperature, and PMMA can craze near a hot chip. For these, tolerance is usually opened to ±0.05 mm unless the function demands more. Copper alloys such as C36000 cut freely and hold fine detail well, which makes them a good fit for small electrical contacts.

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  AluminiumFast, stable, watch thermal growth on long parts.
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  StainlessWork-hardening, keep the edge sharp and the feed up.
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  Titanium and InconelHeat stays in the cut, expect slower cycles.

Surface finish and tolerance are not the same requirement, and confusing them raises cost. An as-machined face at Ra 1.6–3.2 μm is fine for a bracket that only needs to fit. A sealing face or a bearing seat usually wants Ra 0.8–1.6 μm. Optical and vacuum surfaces can need Ra 0.2–0.8 μm, which means slower passes, a different tool and often a finishing operation after machining.

Inspection is where the claim gets tested. We check raw material certificates on arrival, monitor dimensions during the run, and inspect 100% of parts before shipment. Reports are available on request. That sequence catches the failure mode that matters most: a part that was good at the first article and drifted by part 200 because a tool wore or a fixture slipped.

The 99.99% qualification rate we publish is a production figure, not a marketing line. It reflects the fact that tight-tolerance work is judged after measurement, not after cutting. If a feature is out, we know before the parts leave the plant.

For engineers, the useful takeaway is to mark functional surfaces clearly on the drawing. Blanket tolerances across a whole part force the shop to treat every face as critical, which adds cycle time for no functional gain.

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  Mark only what mattersFunctional faces tight, cosmetic faces loose.
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  Finish follows functionRa 0.2–0.8 μm costs real cycle time.
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  Ask for the reportInspection data on request, not by default.

A prototype proves the design. A production run proves the process. The gap between them is usually fixturing and tool life, not the machine. A setup that works for one part may not repeat for 500. We plan the fixture and the tool-change interval at the quoting stage so the first article and part 500 come off the same process.

There is no minimum order quantity. One prototype and a 10,000+ part run go through the same quoting path. Production can start within 24 hours of a released drawing and confirmed order, and parts typically ship in 3–5 days for standard work. Long-run schedules are set per project.

Post-processing is handled in-house: anodizing in clear, colour, hardcoat and conductive variants, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing. Laser marking is available down to a minimum character height of 1.5 mm. Keeping finishing under the same roof avoids the dimensional drift that comes from shipping parts between vendors.

Confidentiality is part of the process. Uploads are secure and confidential, and an NDA is available on request before drawings change hands.

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  No MOQOne part or 10,000+, same route.
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  Finishing in-houseLess handling, fewer dimensional surprises.
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  NDA on requestSigned before drawings are shared.