CNC Jewelry Precision Making

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  What happens between CAD and the finished piece
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  Which material goes on the spindle, and which does not
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  Where the machine stops and the bench starts
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  What tolerance and finish you can actually hold
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  How a jewelry job runs from file to shipment
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  Cut metal direct vs cut a master and cast

CNC jewelry precision making starts with a watertight solid model, not with wax. The CAD file is toolpathed into G code, and a spinning cutter removes material from a solid block or a casting blank. Every pass is a subtraction. The machine does not know the part is jewelry; it only knows depth of cut, stepover and feed rate.

On a 5-axis center the tool and the part move together on X, Y, Z plus two rotary axes. That lets a Ø0.5 mm ball cutter reach under a bezel, into a channel, or behind a prong without the holder crashing into the shank. On a 3-axis machine the same geometry has to be cut in multiple setups, and each remount adds error.

The output is rarely the final ring. Most shops cut a wax or resin master, then cast it. Cutting metal directly makes sense for one-off pieces, for parts that must hold tight fits, and for geometries that would warp in investment casting. Both routes run on the same G code; only the material and the stock setup change.

Feed and speed decide whether the surface comes off clean or smeared. A 0.5 mm cutter in wax runs fast and light. The same cutter in 316L stainless runs slow with flood coolant, because heat builds in the tip and dulls the edge in minutes. Same path, different numbers.

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  Watertight solidOpen shells toolpath badly and leave gouges.
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  5-axis reachCuts undercuts without remounting the part.
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  Wax or metalMaster for casting, or finished part direct.

Wax and machinable resin are the cheapest path to a casting master. They cut in seconds, hold fine detail, and burn out clean in investment casting. If you need 200 identical rings, cut one master and cast the rest. The machine pays for itself once the mold is made.

Silver, gold and platinum cut well with the right tool. Silver 925 is soft and gummy, so it needs sharp carbide and light chiploads or the edges tear. Gold alloys behave better at higher spindle speeds. Platinum work-hardens under the cutter, so a heavier depth of cut and a rigid setup beat many shallow passes.

Stainless 316L, titanium TC4 and 17-4PH are where CNC jewelry precision making separates from hand work. These metals do not cast cleanly at thin sections, and they take a polish that lasts. A machined titanium band can hold Ra 0.8–1.6 μm off the tool with a light finish pass.

Brass C36000 and copper C110 machine freely and are common for prototypes and fashion lines. The trade-off is wear and tarnish. A plated finish solves the surface, but plating adds 5–20 μm per side, and that moves your fits. Budget for it in the model, not after.

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  Wax / resinBest for casting masters and small runs.
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  Gold, silver, platinumDirect cutting works for one-offs and tight fits.
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  Stainless, titaniumMachined because casting warps at thin walls.
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  Brass, copperPrototypes and fashion; plan plating thickness.

A CNC cannot set a stone. Prongs and beads can be cut to tolerance, but the seat and the hammer blow are hand work. If you design a channel setting that assumes the machine will push metal over the stone, the model will not match the bench result.

Deep narrow pockets are the other limit. A slot 0.4 mm wide and 6 mm deep needs a 0.3 mm cutter with a long flute, and that tool deflects. Figure a practical depth-to-diameter ratio of about 5:1 for a clean floor. Past that, expect taper, chatter or a broken tool.

Undercuts and hollow interiors are fine on 5-axis, but the tool still needs a path in and out. A fully enclosed hollow sphere with no opening cannot be cut from solid. It can be cast, or split into two halves and joined.

Mirror polish is not a machining operation. A polished finish starts at the spindle and ends at the wheel. The cutter sets the geometry and the baseline roughness; the polisher removes 2–5 μm of material to reach a bright surface. Leave that stock in the model.

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  Stone settingSeats and beads are hand operations.
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  Depth-to-diameterKeep near 5:1 for stable floors.
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  Enclosed hollowsNo tool entry means cast or split.
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  Polish stockLeave 2–5 μm for the wheel.

GreatLight holds ±0.005 mm (±0.0002 in) on critical features when the geometry allows it. That number applies to a dimension measured on a rigid feature with a clean datum. A thin 0.6 mm shank wall will move under clamping force, and no machine spec fixes that.

Surface finish runs from Ra 0.2–0.8 μm on a fine finish pass to Ra 1.6–3.2 μm as-machined. The finish you get depends on the tool nose radius, the stepover and the material. A 0.2 μm finish on a flat face is routine. The same finish inside a 0.5 mm channel is not.

Inspection is the part most quotes skip. We check raw material, monitor in-process, and inspect 100% before shipment, with reports on request. For a run of 500 earrings, that means every piece is measured against the drawing, not a sample pulled from the bin.

Tolerance and finish drive cost more than size does. Tightening a fit from ±0.05 mm to ±0.005 mm can double cycle time. Ask whether the fit actually needs it, or whether a slip fit with a controlled surface would do the same job.

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  Critical features±0.005 mm holds on rigid geometry.
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  Thin wallsClamping deflection beats machine spec.
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  Finish rangeRa 0.2–0.8 μm fine, 1.6–3.2 μm as-machined.

It starts with a DFM review. We read the model, flag thin walls, deep pockets, tool reach and any feature that will not cut. Quotation and DFM analysis come back within 12 hours. Production can start within 24 hours of approval.

Then the first article. For a new design we cut one piece and measure it before the run. This is the cheapest place to catch a wrong datum or an over-thick prong. Fixing a model costs minutes. Fixing 300 castings costs weeks.

Fixtures come next. A ring is not a block. It needs a custom soft jaw or a sacrificial blank to hold it without crushing the band. Good workholding is most of the difference between a shop that holds ±0.005 mm and one that does not.

Parts ship in 3–5 days for most jobs. There is no minimum order quantity, so a single prototype and a 10,000-piece run go through the same process. Uploads are secure and confidential, and an NDA is available on request.

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  DFM in 12 hoursTool reach, thin walls and pockets flagged.
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  First articleOne piece measured before the run.
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  Ship in 3–5 daysFrom one prototype to 10,000+ parts.