Belarusian CNC External Processing Guide

External machining shapes the outside of a part: outside diameters, shoulders, faces, fillets, chamfers, flats and free-form contours. A lathe turns a cylinder down to size. A mill or machining center cuts pockets that open to the outside, slots along an edge, or a sculpted profile. Grinding and polishing follow when the surface callout is tighter than a cutting tool can hold.

The distinction matters because internal features and external features often need different setups, different tool reach and different inspection methods. A bore you can measure with a plug gauge. An outside contour on a thin wall you measure with a CMM or optical comparator, and the part may deflect under the probe. When you plan belarusian cnc external processing, tell the shop which surfaces are functional and which are cosmetic. That single note changes the fixture, the tool path and the price.

External work is also where five-axis earns its cost. On a three-axis machine, every new face of the workpiece needs a new setup, and each setup adds stack-up error. On a five-axis machine, the tool tilts to the surface instead of the part being re-fixtured. For a part with angled bosses, tapered walls or a curved outer skin, that is the difference between holding ±0.005 mm and chasing it.

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  TurningRotational parts: shafts, bushings, flanges, pistons. Best cost per part for round geometry.
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  MillingPrismatic parts and free-form outside contours, pockets that break the outer wall, angled faces.
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  Mill-turnOne setup for a round part with milled flats, cross holes or an off-axis boss.
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  Grinding and polishingWhen the drawing calls for Ra 0.2–0.8 μm or a sealing face with no tool marks.

Three-axis milling handles a part whose external features all face one direction. It is the cheapest option and still holds ±0.005 mm on a rigid setup. It stops being efficient when the outside geometry wraps around the part. You then pay for extra fixtures and extra setups, and each re-clamp introduces a small error you cannot fully remove.

Four-axis adds rotation around one axis, usually the X or the A axis. It suits parts like a cylinder with milled flats, a manifold with ports on several sides, or a long extrusion with features along its length. The spindle stays vertical, so undercut outer profiles are still out of reach.

Five-axis adds a second rotary axis. The tool can approach the outer surface from almost any direction in one setup. That helps in three concrete ways: shorter tools reach deep outer walls without chatter, angled faces get cut with the tip of the tool rather than the side, and the part stays on one datum from first cut to last. The trade is programming time and a slower cycle on simple features, so we do not put every job on a five-axis center. If a part has one outer face and three holes, three-axis wins.

GreatLight runs 16 simultaneous 5-axis machining centers, 12 four-axis mills and 27 three-axis machines, so the routing decision is made per part rather than per shop policy.

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  Choose 3-axisAll external features on one or two faces, prismatic shape, moderate tolerance.
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  Choose 4-axisRound or long part with features on several sides and no undercut outer profile.
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  Choose 5-axisCurved outer skin, angled bosses, deep outer walls, or a datum that must not move.

Aluminum is the easiest external material. 6061-T6 and 7075 cut fast, hold a sharp edge and take anodizing well. The risk is a soft outer skin that marks easily in handling, so parts with a cosmetic outside surface should go to finishing in protective packaging.

Stainless 304 and 316 work-harden under the tool. A light pass at the wrong feed rubs the surface instead of cutting it, which shows up as a rough outside diameter and rapid tool wear. Heavier feed per tooth and a rigid setup fix most of it. 17-4PH cuts cleaner in the annealed state and can be aged afterward, but the aging distortion has to be planned into the external allowance.

Titanium TC4 (Ti-6Al-4V) and Inconel cost more in tool time than in material. Outside profiles on these alloys need low cutting speed, high coolant pressure and a tool path that keeps the cutter engaged. Thin outer walls on titanium move under cutting force, so we take the last 0.3 mm in light passes on a five-axis center.

Plastics are their own problem. POM and PEEK hold a good outside finish but clamp marks are permanent on soft grades. ABS and PMMA chip poorly and need sharp, polished tools. If the outside surface is visible on the finished product, say so on the drawing.

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  Aluminum 6061-T6, 7075Good external finish, anodizing friendly, fast cycle.
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  Stainless 304, 316L, 17-4PHControl feed to avoid work hardening on the outer skin.
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  Titanium TC4, InconelSlow speeds, rigid setup, light finishing passes on outer walls.
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  POM, PEEK, ABS, PMMAWatch clamping pressure and chip evacuation on the outside surface.

The tolerance on an outside surface should match what the part does. A mounting boss that locates a bearing needs ±0.005 mm. A cover that only keeps dust out does not. When every dimension on the drawing carries the same tight tolerance, the shop has to assume the tightest case and the price climbs for no functional gain.

Datums matter more on external work than many drawings admit. If the outside diameter is the datum and the part is turned from bar stock, the datum is set at first grip. If the part is milled from plate and the outside is the reference, the plate edge must be squared before anything else is cut. Call out which surface is the master. Two datums on one drawing that cannot both be true at the same time is the most common cause of a back-and-forth during DFM review.

For surface finish, be specific about where it applies. A note that says Ra 0.8 μm across the whole part usually means the shop polishes everything. A note that puts Ra 0.8 μm on one sealing face and Ra 3.2 μm elsewhere is cheaper and just as functional. GreatLight sends a free DFM analysis with the quotation within 12 hours, and we flag these points before cutting metal.

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  Tolerance by functionTight where it locates or seals, open where it only covers.
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  One master datumState which external surface is the reference for the rest.
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  Finish by zoneRa 0.8–1.6 μm on functional faces, Ra 1.6–3.2 μm elsewhere.

External dimensions are checked with micrometers, bore gauges and CMM depending on the feature. A round outside diameter on a shaft is measured at several stations along its length, because taper hides in a single reading. A free-form outer contour is checked against the CAD model on a CMM, with probe radius compensation verified first.

GreatLight inspects 100% of parts before shipment. The sequence is raw material check on arrival, in-process monitoring during cutting, and final inspection before packing. Inspection reports are available on request. The historical qualification rate is 99.99%, and the historical late-delivery probability is below 2%.

For Belarusian buyers, the practical question is documentation. Certificates for ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 are on file. If your project needs a first article inspection report, dimensional report or material certificate, ask at the quotation stage so it is built into the schedule rather than added at the end.

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  In-processOperator checks at defined intervals, not only at the end.
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  Final100% inspection before shipment, reports on request.
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  ConfidentialityUploads are secure and confidential; NDA available on request.