Precision CNC Quotation Guide

• 1
  What a CNC quotation guide is really measuring
• 2
  Geometry and setup count drive most of the price
• 3
  Material choice sets the cutting speed, not the price list
• 4
  Tolerance and finish are where quotes diverge most
• 5
  Inspection, finishing and lead time add the last layer
• 6
  How to compare two precision CNC machining quotations
• 7
  Step by step: what to send for an accurate quote
• 8
  How each driver moves a precision CNC quotation

A machinist does not price a part. He prices the time, the tool wear, the fixturing, the inspection and the risk of scrapping it. When two shops return numbers that differ by 40 percent, they usually disagree about one of those five things, not about the part itself.

So the useful question is never "why is this expensive". It is "which driver is doing the work in this number". A 200 mm aluminium bracket at ±0.1 mm and the same bracket at ±0.005 mm are different products. They should not cost the same, and no honest shop will quote them the same.

This CNC quotation guide walks through the drivers in the order a process engineer actually evaluates them: geometry, setup count, material, tolerance, surface finish, inspection and lead time. Read it once and you can tell which quote is cheap for a reason.

One boundary up front: quotes for turning, milling, five-axis work and sheet metal are built from different time models. Comparing a milled quote against a turned quote tells you nothing. Compare like with like, or ask the shop to break the number down.

Geometry decides how many directions the cutter must approach from. A part with pockets on one face is a one-setup job. Add cross-drilled holes, an undercut or a contoured back face and you either add setups or move to a machine that can reach all of it without re-clamping.

Every extra setup adds three costs at once: the fixturing itself, the re-datum error introduced when the part is moved, and the labour to prove the new zero. That third cost is the one buyers forget. Re-clamping a part to ±0.02 mm takes longer than cutting it.

This is where simultaneous 5-axis work changes the arithmetic. Our 16 five-axis machining centers hold a part in one orientation and rotate the tool or table through the feature. No re-datum, no second fixture, no stack-up. On a part with features on four faces, that usually removes two setups entirely.

Not every part deserves five axes. A flat plate with through-holes should be cut on a 3-axis machine, and quoting it on a five-axis center only raises the hourly rate. We keep 27 three-axis machines and 12 four-axis mills for exactly that reason. Match the machine to the geometry, then price the geometry.

• 1
  One face of features3-axis, single setup, lowest cost per part
• 2
  Features on 2-3 faces4-axis or 3-axis with a second op
• 3
  Contoured or angled features on 4+ facesSimultaneous 5-axis, one setup
• 4
  Deep cavities, thin wallsLong reach tooling, reduced feed, higher time

Material cost is the visible line. Cutting speed is the invisible one. Aluminium 6061 machines at high spindle speed with generous feed, so cycle time is short and tool life is long. Titanium Ti-6Al-4V conducts heat poorly, work-hardens at the cut and forces low feed rates, so the same pocket can take four times longer.

Stainless 316 and 17-4PH sit in the middle. They are machinable but gummy, and they punish light finishing passes. Inconel sits at the far end: it may need carbide at reduced speed and a rigid setup, and small shops often decline it rather than quote it badly.

Material also drives stock removal strategy. A part machined from 7075 plate might need 60 percent of the blank turned into chips. A casting or near-net forging reduces that, but adds tooling cost and lead time. For runs above a few hundred pieces, that trade is worth modelling.

Our material list runs from 6061, 2024 and 7075 aluminium through 303, 304, 316L, 17-4PH stainless, 4130 and 4140 steel, C36000 brass, TC4 titanium, Inconel, magnesium and engineering plastics such as POM, PEEK and carbon fibre. Ask us which of them we would actually recommend for your geometry.

A general tolerance block of ±0.1 mm lets the machinist cut, measure with calipers and move on. Tightening one bore to ±0.005 mm forces a different workflow: a warm-up cycle, temperature-stable coolant, a finishing pass with a fresh tool, and a CMM check that may take longer than the cut.

The cost is not linear. Going from ±0.1 mm to ±0.05 mm is usually a small step. Going from ±0.02 mm to ±0.005 mm is a large one, because you are now controlling thermal growth and tool deflection rather than just measuring them. Apply the tight tolerance only where the function demands it.

Surface finish behaves the same way. Ra 1.6–3.2 μm is a normal machined surface. Ra 0.8–1.6 μm needs a controlled finishing pass. Ra 0.2–0.8 μm usually means a separate operation: fine boring, lapping or polishing, and possibly masking the surfaces that must stay as machined.

A practical habit: mark the drawing with the two or three features that genuinely need tight tolerance and fine finish, and leave the rest general. That single change often removes more cost than switching suppliers, and it keeps the critical features honest.

Inspection is a real line item, not overhead. Every part we ship passes raw material check, in-process monitoring and final inspection, with reports available on request. If your drawing calls for a full dimensional report or first-article inspection on every part, that is measurement time, and it belongs in the quote.

Post-processing adds operations and handling. Anodizing, hardcoat, electroless nickel or zinc plating, powder coating and black oxide all require a separate process step and often a masking step. Bead blasting, tumbling, brushing and polishing change the geometry slightly at the edges, so they must be specified before cutting, not after.

Lead time is the driver buyers negotiate hardest and understand least. Standard flow gives a quotation and free DFM analysis within 12 hours, production start within 24 hours, and parts shipping in 3–5 days. A compressed schedule means reshuffling the machine queue, which costs more than the machining itself.

All four quality systems we hold matter to different buyers: ISO 9001:2015 for general manufacturing, IATF 16949:2016 for automotive, ISO 13485:2016 for medical devices and ISO 27001:2022 for information security. If your part needs one of them, say so in the RFQ. It changes who runs the job.

Put both quotes side by side and check the assumptions, not the totals. Does each one state the tolerance on the tight feature? Does it list the material grade, including temper? Does it name the finish and the inspection level? A quote that omits all three is not comparable, it is just a number.

Next, look for the operation count. If one quote lists three operations and the other lists five, the difference is setup time, and you can ask why. Sometimes the answer is a fixture the shop already owns, which is a genuine advantage. Sometimes it is a machine that cannot reach the feature in one pass.

Ask what happens on a revision. A shop with 127 CNC machines and 150 technicians can absorb a small change between quote and cut. A shop that outsources its grinding and anodizing cannot. Ask who does the finishing, and whether it happens in house.

Finally, check the scrapping policy in writing. Nobody guarantees zero scrap on a first article. What matters is whether the shop flags an unbuildable feature before cutting, and whether it tells you instead of shipping it.