Can Platinum Be CNC Machined?

Pure platinum sits around 37 to 42 HV on the Vickers scale in the annealed state. That is softer than 6061 aluminium and roughly in the same range as fine silver. A sharp tool does not push hard against the grain the way it does in 4140 or 17-4PH. Instead the edge tends to plow, and the chip can weld to the rake face within a few revolutions if the surface speed is wrong.

The density is the second factor. Platinum runs about 21.45 g/cm³, so a bar 25 mm in diameter and 300 mm long weighs roughly 3.2 kg. Every gram you cut away is money on the floor, and the workpiece itself carries enough inertia that light finishing passes need a rigid setup. On a 16 simultaneous 5-axis center, that inertia shows up as chatter if the part is held too far from the vise.

Alloying changes the picture. Adding iridium, ruthenium or rhodium raises hardness and grain stability. Pt-Ir 90/10 machines noticeably cleaner than pure Pt because the iridium restricts grain growth and reduces the built-up edge. Pt-Ru 95/5 behaves similarly and is common in electrical contacts. The trade-off is cost and, for some medical work, biocompatibility paperwork.

Thermal conductivity is low, around 72 W/m·K. Heat does not leave through the chip fast, so it concentrates at the cutting edge. That is why coolant delivery matters more here than in aluminium work, and why a dull tool burns the surface finish before it breaks.

Carbide is the standard choice. Uncoated micro-grain carbide with a sharp, positive rake works better than a coated insert for most platinum jobs, because coatings tend to spall under the low-speed, high-pressure contact this material produces. Diamond-tipped tooling is the next step up for optical or sealing surfaces where Ra 0.2–0.8 μm is required.

Keep surface speed low. A practical band is 30 to 60 m/min for turning with carbide, and 60 to 100 m/min if you move to PCD or diamond. Feed per tooth should stay high enough to keep the edge cutting rather than rubbing; 0.05 to 0.15 mm per tooth on a 6 mm end mill is a reasonable starting point. Depth of cut can be generous in roughing because the material is soft, but leave 0.2 to 0.3 mm for finishing.

Coolant choice is not optional. Water-soluble flood coolant at 6 to 8 percent concentration keeps the edge cool and flushes chips. Some shops run neat oil for tapping and fine boring. Never run platinum dry on a finishing pass; the chip will smear and you will spend more time polishing than the cycle saved.

For drilling, use 118° or 135° point angles with polished flutes and peck deeper than you would in steel. Platinum chips are ductile and stringy, so chip evacuation is the main limit on hole depth. Anything past 5× diameter benefits from through-tool coolant or a peck cycle with full retract.

CNC makes sense for platinum when the part needs tight tolerances, an internal feature, or a geometry that a die cannot form. Our 5-axis centers hold ±0.005 mm on small platinum parts, and mill-turn centers handle features that would otherwise need two setups. For a hundred contact pins with a stepped profile, that is the right call.

It stops making sense when the part is a simple flat washer or a thin sheet blank. Stamping or laser cutting leaves almost no scrap and skips the tool wear. The material cost dominates the part cost in every platinum job, so process selection should start with how little you can remove, not how fast you can remove it.

Thin walls are a real constraint. Below about 0.5 mm, platinum deflects under clamping force and the finishing pass chatters. Design a thicker boss where the part is held and machine it away last, or plan a sacrificial tab. We have run walls down to 0.3 mm, but that requires light passes, sharp tooling and a fixture that supports the wall from behind.

If your part is a prototype and the geometry is still moving, rapid prototyping in a platinum alloy is rarely cost-effective. Most teams prove the design in aluminium or 316 stainless first, then cut the platinum version once the drawing is frozen. That sequence saves both material and revision cycles.

Clamping is where most platinum jobs go wrong. Soft jaws machined to the part profile spread the load and avoid jaw marks on a finished face. Vacuum chucks work for thin plates. Magnetic workholding is useless here. For a part with a mirror finish on one side, cut that face last and hold on a roughed surface.

Inspection follows the same logic as any precision job. Raw material certificate check, in-process measurement on critical diameters, and a final inspection before shipment. Reports are available on request. For platinum, a material certificate matters because alloy grade drives both hardness and price.

Scrap recovery is part of the quote. Chips, test cuts and rejected parts all have value as refined metal, and a shop that tracks them can price the job more accurately. Ask how scrap is handled before you approve a process plan.

Lead time is driven by material procurement, not machine time. Once stock is on the floor, production can start within 24 hours and parts ship in 3–5 days. The 12-hour quotation and free DFM analysis is where we flag thin walls, deep holes and features that will fight the material.