CNC Processing Costs Explained

• 1
  What sets the price
• 2
  Cost drivers and how much they move the price
• 3
  Why CNC processing costs explained by tolerance alone is misleading
• 4
  Setup, programming and the cost of a new design
• 5
  Material, stock removal and what you throw away
• 6
  Prototype quantities and how the method changes
• 7
  Finishing, inspection and the costs added after machining
• 8
  Six steps to compare CNC quotes on the same basis

Tolerance is the most quoted cost driver and the most misunderstood. A ±0.005 mm callout does not simply mean a slower cut. It means the shop has to hold the part at a stable temperature, take lighter passes, and measure between them. On a 200 mm aluminum bracket, tightening two bores from ±0.05 mm to ±0.005 mm can add a full finishing pass and a CMM check on every part.

The trap is applying tight tolerance everywhere. Engineers often carry a default tolerance block across the whole drawing because the assembly needs it in one place. Redraw it. Mark the two datum features that matter, loosen the rest, and the quote usually drops before the supplier does anything clever.

Material hardness changes how tolerance translates into time. In 6061-T6 you can chase ±0.005 mm with sharp carbide and light depths of cut. In 17-4PH or Ti-6Al-4V the same callout means slower speeds, more tool changes and a higher risk of scrapping the part at the final op. That risk is priced into the quote.

One more point that rarely appears on a drawing: measurement. If a feature cannot be reached by a CMM probe, the shop needs a custom fixture or a gauge. That cost is real and it lands on your part whether the drawing mentions it or not.

For a one-off prototype, setup and programming can be 60% of the invoice. The spindle may run for 40 minutes, but someone still has to read the model, choose toolpaths, build soft jaws and prove the first part. This is why the second identical part is dramatically cheaper than the first.

Programming time scales with complexity, not with size. A 4,000 mm rail with simple pockets may take less CAM time than a fist-sized manifold with five intersecting bores. When you send a model, the shop is also checking whether the part can be reached at all. Every face that needs a second or third orientation adds a setup.

Five-axis machines cut setup count. On a part with features on four sides, 5-axis can often hold one datum and machine it in a single operation. Our 16 simultaneous 5-axis centers exist for exactly this case. The trade is a higher hourly rate against fewer hours and better positional accuracy between faces.

If you are still in design, ask for a DFM pass before the drawing is released. A free DFM analysis inside 12 hours is cheaper than discovering a wall too thin to hold after the tooling is cut.

Material cost is not just the price per kilogram. It is the price of the billet you buy minus the chips you sell. A part machined from a 150 mm bar when it fits in a 100 mm bar costs more in two ways: higher stock price and more roughing time to remove the excess.

Exotic alloys widen the gap. Titanium and Inconel cost several times more per kilogram than 6061, cut at a fraction of the speed, and wear tools faster. Inconel in particular work-hardens if the cutter dwells, so the programmer has to keep the feed up and the radial engagement controlled. That is skill, and skill is billed.

Plastics behave differently again. POM and PEEK machine fast but move with temperature, so thin walls need care. Carbon fibre eats tool edges. None of this is visible in a per-kilogram price.

The practical move is to specify the cheapest alloy that meets the function and to size the stock close to the finished part. If you are unsure, send the model and we will tell you which of our stocked grades, from 6061 and 7075 to 316L and Ti-6Al-4V, fits the load case.

Below about 50 parts, machining from billet usually wins. The tooling is just soft jaws and a program, so the fixed cost is low and the parts are identical. Unit price falls steeply as that fixed cost is spread, then flattens once you are paying mostly for material and cycle time.

Above a few thousand parts, other processes start to compete. Die casting and vacuum casting move the cost into tooling and out of cycle time. The crossover depends on geometry, wall thickness and the finish you need. A cast part often needs a machining pass on the critical faces anyway, so the two processes are not exclusive.

We run no minimum order quantity, from one prototype to 10,000+ part runs, because the decision should follow the geometry rather than our scheduling. If a job is drifting toward a process we do not run, we say so.

Be careful with quotes that assume a different process than you intended. A price built on casting is not comparable with one built on billet machining, even if the part number matches. Ask which process the number assumes.

A part leaving the machine is rarely finished. Anodizing, plating, powder coating, bead blasting and laser marking each add a line. Hardcoat anodizing costs more than a clear decorative coat. Laser marking needs at least 1.5 mm character height to stay legible, which sometimes forces a drawing change.

Inspection is the line buyers question most and regret cutting. On a loose bracket, a sample check is fine. On a medical or automotive part with a tight bore, 100% inspection before shipment is the only way to know the lot is good. Our standard flow is raw material check, in-process monitoring and final inspection, with reports on request.

Certifications shift cost in a way that is easy to miss. ISO 9001:2015 covers general quality. IATF 16949:2016 and ISO 13485:2016 add traceability, document control and validation work that shows up in the quote. ISO 27001:2022 covers how your files are handled. If your program requires these, filter suppliers on them first.

Finishing and inspection are also where lead time is lost, not just money. Outsourced anodizing can add days. Ask whether finishing is in-house or subcontracted before you commit to a date.