How CNC fee calculation sets your unit price

• 1
  How a quote is built, line by line
• 2
  Why geometry drives cycle time more than size
• 3
  Material cost, yield, and the buy-to-fly ratio
• 4
  How batch size divides the fixed costs
• 5
  Finishing, inspection, and the tolerance tax
• 6
  What moves the price, and by how much

Every quote we send is the sum of five numbers: setup time, machine time, material, finishing, and inspection. Nothing else. When a price looks strange, it is almost always one of those five that moved. Not the exchange rate, not a vague overhead line.

Setup is a fixed cost per batch. Fixture building, first-article checks, tool presetting and program proving land here. On a simple 3-axis part that might be 30 minutes. On a 5-axis part with two re-fixturings it can run past 3 hours. Divide that by batch size and you see why ten parts cost far more per piece than a thousand.

Machine time is the hourly rate times the cycle. The rate reflects the machine, not the part: a 3-axis mill, a mill-turn center, and a simultaneous 5-axis center all carry different rates because they cost different amounts to buy, run and keep calibrated. Cycle time is where design decisions show up. A pocket with a 3 mm corner radius forces a small tool, and small tools must run slower and take lighter cuts.

Material is not just the bar price. It is the bar price times the buy-to-fly ratio. If a bracket is machined from a 100 × 100 × 50 mm block down to a 30 g finished part, you paid for the whole block and turned most of it into chips. Near-net forgings or extrusions cut that waste, sometimes by half.

A 200 mm aluminum plate with open pockets can finish faster than a 40 mm steel block full of deep ribs. Size sets the travel envelope. Geometry sets the toolpath length, the number of tools, and how many times the part has to be repositioned.

Three features push cycle time up hard. Deep pockets with a depth-to-diameter ratio past 4:1 need long, thin tools that chatter, so feed rates drop. Thin walls below 1 mm deflect under cutting force, so you take spring passes. Tight true-position callouts on many holes force single-point boring instead of drilling.

Five-sided access is the other lever. If a part has features on five faces, a 3-axis machine needs three or four setups, each with its own fixture and alignment error. A simultaneous 5-axis center reaches those faces in one setup. The machine rate is higher, but the setup count and the accumulated tolerance stack both shrink. On complex parts the total often comes out lower.

This is why we ask for a STEP file, not a drawing alone, before quoting. The solid tells us tool reach, stock removal volume and the number of setups. A drawing tells us what the part must be, not how much work it takes to get there.

Material is quoted by weight, but you pay for the stock you remove as well as the stock you keep. Buy-to-fly ratio is finished weight divided by purchased weight. A ratio of 0.2 means 80% of what you bought became chips. That is normal for a complex aerospace bracket and wasteful for a simple spacer.

Alloy choice changes both the price per kg and the machinability. 6061-T6 cuts cleanly at high surface speed and is the default for prototypes. 7075 is stronger but gummier and needs sharper tools and more coolant. 316L stainless work-hardens if the tool rubs instead of cuts, so feed per tooth has to stay above a floor. Inconel and Ti-6Al-4V sit at the far end: low thermal conductivity, high cutting temperature, tool life measured in minutes.

Certification adds a line too. If the part is destined for a medical device or a flight component, the mill certificate and heat-lot traceability come with the bar. That paperwork is real cost, and it is not negotiable on those programs.

One practical move: send us the stock form you already have, or ask what near-net shape we would buy. Switching from plate to extrusion on a long part can remove a large share of the roughing time and the scrap.

Fixed costs do not care how many parts you order. Setup, fixturing, programming and first-article inspection happen once. Spread over 5 parts they dominate the price. Spread over 500 they nearly vanish. This is the single biggest reason a prototype quote looks alarming next to a production quote.

There is a second effect that works the other way. High-volume runs justify a dedicated fixture, custom soft jaws and optimized toolpaths. Those cost money up front but cut cycle time per part. Somewhere in the middle there is a batch size where the curve flattens and adding parts stops helping much.

We run no minimum order quantity, from one prototype to 10,000+ part runs. That means you can order the five parts you need for fit checks without paying a penalty, then move to a larger run once the design freezes. Quoting both at once usually shows the crossover point clearly.

If your volumes are uncertain, ask for a small-lot price and a production price side by side. The gap tells you how much of the fee is fixed and how much is variable. That ratio is more useful than either number alone.

As-machined surfaces sit around Ra 1.6–3.2 μm and cost nothing extra. Pushing to Ra 0.8–1.6 μm usually means a finishing pass with a smaller stepover, which adds cycle time. Below that, Ra 0.2–0.8 μm, you are into extra operations and sometimes hand polishing. Each step is a real cost, so specify the finish the function needs, not the best one available.

Coating and plating add both cost and lead time because they leave the shop. Anodizing, electroless nickel, zinc plating, powder coating and black oxide all run through outside processes with their own queues. Laser marking is cheaper but has a floor: minimum character height is 1.5 mm, so a 0.5 mm serial number is not going to happen.

Tolerance is the quiet driver. A general ±0.1 mm profile is routine. Tightening a bore to ±0.005 mm means the machine has to hold it, the operator has to measure it, and the inspection report has to prove it. That chain costs money at every link.

Ask yourself which dimensions actually matter. If three features need tight tolerance and the other forty do not, say so on the drawing. Blanket tight tolerances across a part are the most common way to pay for precision you will never use.