CNC Processing Cost Per Hour: 7 Faults in Quotes

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  Key takeaways
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  What each CNC processing cost per hour line should contain
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  What the CNC processing cost per hour actually pays for
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  Machine class and cycle time: the two real drivers
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  Batch size, setup and how the hourly rate stops mattering
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  Tolerance, finish and inspection scope
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  Seven faults that show up in hourly rate quotes
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  Step by step: compare two hourly rate quotes

An hourly rate is a recovery number, not a profit number. It spreads the cost of owning and running a machine across the hours that machine is expected to sell. Depreciation, floor space, power, coolant, compressed air, maintenance, tooling consumables and the operator's wage all sit inside it. When a shop tells you $75 per hour, that figure already assumes a certain number of billable hours per month.

That assumption is the weak point. A shop running one shift recovers the same machine cost across fewer hours than a shop running three. The second shop can quote a lower rate and still be fine. The first shop either quotes higher or quietly shortens its cycle-time estimate. Neither number tells you which shop will deliver on time.

So the useful question is not what is your hourly rate. It is what is included in that rate, and what gets billed separately. A shop that answers that clearly is usually the one that also answers emails clearly.

Shift count, spindle utilization and the mix of simple versus complex work all push the recovery number around. Two shops with identical machine lists can sit 40% apart on rate and still be equally profitable.

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  Ask for the inclusion listMachine, programming, setup, inspection scope and tooling should each be named.
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  Ask what triggers a re-quoteDesign change, tolerance change or quantity change should have a stated threshold.

Machine class sets a hard floor on the rate. A 3-axis mill with a 500 × 500 × 450 mm envelope is the cheapest hour you can buy. A simultaneous 5-axis center with a Ø400 mm rotary table costs several times more per hour, because the machine costs more, the CAM work is heavier and the operator needs more skill.

Cycle time then decides how many of those expensive hours you actually buy. A part that takes 40 minutes on a 3-axis machine at a low rate can cost less than the same part taking 12 minutes on a 5-axis machine at a high rate. This is where the comparison usually goes wrong. Buyers compare rates. They should compare total machine hours per part.

Rigidity matters too. Thin walls, long reach and hard materials force lighter cuts and slower feed rates. In titanium such as TC4 (Ti-6Al-4V) or Inconel, tool life drops fast and the shop has to slow down to hold ±0.005 mm. The hourly rate may not change at all, but the hours will.

A part with deep pockets and tight corner radii is a 5-axis job. A flat bracket with drilled holes is not. Paying 5-axis rates for 3-axis geometry is one of the most common ways to overspend.

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  3-axisPrismatic parts, flat faces, drilled patterns, wide open tolerances.
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  4-axis and mill-turnCylindrical features, slots around a diameter, parts needing one rotary index.
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  5-axisUndercuts, compound angles, deep cavities, single-setup accuracy on five faces.

Setup is a fixed cost. On a one-off prototype, setup and programming can take longer than the cut. The hourly rate is then a small part of the invoice, and negotiating it hard is a waste of everyone's time. On a 10,000-part run, setup disappears into the noise and the cycle time becomes almost the entire price.

That is why the same part can show a very different cost per hour at quantity 1 and quantity 5,000. The rate did not change. The ratio of setup hours to cutting hours did. Any quote that does not state a quantity is not a quote, it is a starting position.

Fixturing is the quiet cost. A part with no natural datum needs a soft jaw set or a custom fixture. That fixture is engineering time, material and machine time, and it is usually billed once. If you plan to reorder, ask whether the fixture is kept and whether the second run is cheaper.

Tooling wear scales with material removed, not with hours. Hardened steel and 17-4PH stainless eat inserts. Aluminum 6061 barely touches them. Two parts with the same cycle time can have very different tooling cost buried in the same rate.

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  Quantity 1–10Setup and programming dominate. Expect the highest cost per part.
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  Quantity 100–1,000Setup amortizes. Cycle time and material become the main lines.
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  Quantity 10,000+Cycle time is nearly everything. A 10% cycle cut is a 10% price cut.

Tolerance is not free. Holding ±0.005 mm requires a machine in good condition, temperature control, sharp tooling and more frequent in-process checks. A drawing calling ±0.005 mm on every dimension will cost more than one calling it on three critical features and general tolerance elsewhere.

Surface finish behaves the same way. As-machined at Ra 1.6–3.2 μm comes off the tool with no extra work. Ra 0.8–1.6 μm needs a finishing pass with a smaller stepover. Ra 0.2–0.8 μm usually needs a separate operation, sometimes hand polishing on complex geometry. Each step adds hours, not rate.

Inspection scope is the line most often missing from a quote. A shop that checks parts visually and ships is not the same as a shop that runs a CMM program, records the results and keeps them on file. The second shop is more expensive. It is also the one you want when the part goes into a medical device or an engine bay.

Full inspection before shipment, with reports on request, is a normal expectation for regulated work. If a quote does not mention inspection at all, assume it is visual only.

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  Ask which dimensions are criticalMark them on the drawing. Shops price what they can see.
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  Ask for the inspection recordA sample report tells you more than a certificate PDF.

Fault one: a rate with no quantity. Without a lot size, the number means nothing. Fault two: no material grade stated. Aluminum 6061 and 7075 machine differently and cost differently. Fault three: finish listed as standard with no Ra value.

Fault four: inspection not mentioned. Fault five: the quote assumes the customer supplies the CAD model in a clean, manufacturable state. Real models have missing tolerances, thin walls and tool radii that cannot be cut. A DFM review catches these before they become change orders.

Fault six: lead time quoted as a range with no trigger. A shop that says 3–5 days without stating what starts the clock is telling you very little. Fault seven: no statement on confidentiality. Parts under NDA need a process, not a promise.

None of these faults are dishonest. They are gaps. A complete quote names the material grade, the quantity, the tolerance class, the finish value, the inspection scope, the lead time start point and the confidentiality arrangement. Everything else is negotiation.

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  Missing quantityCost per hour cannot be evaluated without a lot size.
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  Missing finish valueStandard finish is not a specification.
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  No confidentiality termsAsk for an NDA before you send production files.