CNC Cost Accounting Table: What a Quote Really Contains
Every CNC cost accounting table breaks a part price into material, machine time, labor, setup and overhead. Read it before you compare suppliers, because the lowest number is often the one with the least detail behind it.
In this article
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Five things to check first
How cost lines behave as volume changes
Use this to decide which line to negotiate and which to leave alone.
| Cost line | Behavior at 10 pcs | Behavior at 1,000 pcs | Where to push |
|---|---|---|---|
| Material | Per-part, plus cutting stock | Per-part, drops 10–20% | Bar size and nesting |
| Setup | Dominates the unit price | Spreads thin, often waived | Fixture reuse across runs |
| Machine time | Per-part, near flat | Per-part, small gain | Cycle time and tool path |
| Labor | Per-part, high touch | Per-part, drops with pallets | Lights-out capacity |
| Tooling | Per-part, full insert cost | Per-part, amortized | Tool life and feeds |
| Inspection | Per-part, 100% if required | Sampling may apply | Drawing tolerance callouts |
| Finishing | Per-part, batch minimum | Per-part, batch efficient | Masking and rack density |
| Overhead | Fixed hourly rate | Fixed hourly rate | Nothing without changing shop |
Compare the table, not the total
The cheapest quote is often the one with the fewest lines. Get the six cost lines, a separate setup figure and an assumed cycle time, then decide.
What belongs in a CNC cost accounting table
A quote is a summary. The table underneath it is where the money lives. Six lines cover almost all machined parts: raw material, machine time, setup, labor, tooling and finishing. Add inspection and overhead if the shop tracks them separately. When a supplier sends one lump number, you cannot tell whether the price is driven by a hard feature or by an old hourly rate.
Material is quoted by the bar or plate you actually buy, not by the finished weight. A Ø80 mm aluminum part cut from Ø100 mm bar carries 36% more material cost than the finished part suggests. Ask how the stock was chosen. Sometimes a different bar size or a near-net forging removes that gap without changing the drawing.
Machine time follows the feature list. Deep pockets, thin walls, tight tolerances and five-axis blending all add minutes. A part that looks simple in CAD can need three setups and two fixtures. Cycle time estimates of 20–40 minutes for a medium-complexity 300 mm part are normal on a 3-axis mill; the same part on a 5-axis center may run 12–25 minutes with one setup.
Setup and labor: the lines buyers misread
Setup is a one-time cost. It does not shrink when the quantity grows, and it does not belong in a per-part rate. A fair quote lists it separately: fixture design, first-article proving, program verification. For a 10-piece run, setup can be 30–50% of the total. For a 1,000-piece run it may fall under 2%.
Labor is often folded into the machine rate, which hides the real driver. On a 3-axis mill one operator may tend one machine. On a mill-turn center with a bar feeder, one operator can tend several. The labor content per part differs by a factor of three or more between those setups, and it shows up in the rate, not the cycle time.
Watch for a setup charge that appears again on a repeat order. Reusing an existing fixture and proven program should reduce or eliminate it. If the second order carries the same setup line, the shop is either rebuilding the fixture or padding the quote. Both are worth a question. A documented fixture number on the quote settles it in one email.
Tolerance, finish and the cost step they create
Tolerance is not a smooth scale. Cost jumps in steps. Going from ±0.05 mm to ±0.025 mm usually adds a finishing pass and more inspection. Going from ±0.025 mm to ±0.005 mm can add a temperature-controlled room, a jig borer or a grinder, and a full CMM report on every part. The last step can double or triple the unit price.
Surface finish behaves the same way. As-machined at Ra 1.6–3.2 μm comes off the cutter with no extra operation. Ra 0.8–1.6 μm may need a finer stepover or a second pass. Ra 0.2–0.8 μm usually means lapping, polishing or a dedicated finishing cell. Mark the finish only where it matters: sealing faces, bearing bores, sliding surfaces. Blanket finishes on a drawing are the easiest cost to remove.
Position tolerance is the line most often ignored. A hole pattern at ±0.1 mm can be drilled on a 3-axis machine with a vise. The same pattern at ±0.01 mm true position may need a horizontal machining center, probing, and a fixture that holds the part the same way every cycle. Read the GD&T frame before comparing quotes. A shop that quotes both versions at the same price is not reading the drawing.
How quantity changes the table
At low volume the table is dominated by setup and programming. A single prototype can carry 60% non-recurring cost. That is normal, and it is why prototype prices look high per part. The number to watch is the recurring cost, not the first invoice. Ask for both. A shop that separates them gives you a usable baseline for the production run.
In the middle range, from about 50 to 500 pieces, machine time and material take over. This is where cycle time optimization pays. A 15% cycle time cut on a 500-piece order saves more than negotiating the hourly rate by 5%. It also compounds: the tool path, the fixture and the inspection plan all get reused on the next order.
At high volume, above 1,000 pieces, the calculus changes again. Casting, forging or extrusion may beat machining from bar stock. The CNC cost accounting table should show the crossover point. If machining a 200 g aluminum bracket costs $8 at 5,000 pieces, and a die casting lands near $3 with tooling amortized over the same run, the table should say so instead of quietly quoting the mill.
Judging the supplier behind the table
A clean table is worth little if the shop cannot hold the tolerance. Match the claimed capability to the machine list. Five-axis simultaneous work needs a real 5-axis center, not a 3-axis mill with a tilting vise. If the part has a 4,000 mm envelope, the shop needs a machine that travels that far. Vague answers here predict late delivery later.
Certifications matter by industry. ISO 9001:2015 covers general quality systems. IATF 16949:2016 is expected for automotive and EV work. ISO 13485:2016 applies to medical devices, and ISO 27001:2022 covers information security for customer drawings and CAD files. Ask which certificate covers the plant that will actually run your part.
Check the quoting process itself. A supplier that returns a DFM note with the price is telling you it read the model. One that returns a number in an hour with no questions either has seen the part before or has not opened the file. The second case is common, and it shows up as a change order two weeks into production.
How to build and use the table
Seven steps from RFQ to a comparable quote.
- 11. Fix the drawing before you send itSet tolerances only where the function needs them. Blanket ±0.005 mm on a 300 mm part raises cost across every feature. Confirm the finish callouts are on the faces that touch something.
- 22. Send the model, the 2D drawing and the quantity rangeGive the low, middle and high volume you expect. A single quantity forces the shop to guess, and guesses are padded. Note any target date so lead time enters the table early.
- 33. Request the quote broken into the six cost linesMaterial, machine time, setup, labor, tooling, finishing. Add inspection and overhead if the shop tracks them. A one-line quote cannot be compared to a detailed one.
- 44. Separate non-recurring from recurring costSetup, programming and fixture cost are one-time. Unit price is recurring. Put both on the table so the prototype invoice does not distort the production decision.
- 55. Ask for the assumed cycle timeA quote that assumes 15 minutes when the part needs 40 will come back as a change order. Compare the assumption to the feature list: pocket depth, wall thickness, number of setups.
- 66. Confirm the inspection and documentation planFirst article, in-process checks, final inspection, material certs, CMM reports. Decide which you need and put them in the table as a line, not as an expectation.
- 77. Re-quote at three volumes and find the crossoverRun 10, 100 and 1,000 pieces through the same table. The point where a different process wins should be visible. If it is not, ask the supplier to model it.
Common questions
Why do two shops quote the same part 30% apart?
Most of the gap sits in the hourly rate and the assumed cycle time. A shop running older 3-axis machines with manual load may charge a lower rate but need 40 minutes per part. A shop with a pallet-fed 4-axis mill charges more per hour and finishes in 12 minutes.
The second gap is setup treatment. One shop amortizes fixture cost across the order, the other bills it as a lump. Compare the total, not the unit price, and check whether setup is charged again on the repeat order.
Should setup be a separate line on the quote?
Yes. Setup is a fixed cost that does not scale with quantity. Folding it into the unit price makes small runs look expensive and large runs look artificially cheap. It also hides whether the shop is reusing an existing fixture.
On a repeat order, ask for the setup line to be removed or reduced. If the fixture and program already exist, the cost is gone. A shop that keeps charging it is either rebuilding the fixture or padding the quote.
How much does tolerance actually add?
From ±0.05 mm to ±0.025 mm, expect a 10–25% increase from extra finishing passes and inspection. From ±0.025 mm to ±0.005 mm, expect 50–100% or more, because the process changes: temperature control, grinding or jig boring, and full CMM verification.
The practical move is to relax tolerances on features that do not function. Cosmetic surfaces, clearance holes and non-mating edges rarely need the tight callout. Removing three tight tolerances can cut more cost than switching suppliers.
Does a low-volume run ever make sense?
Yes, when the part is a prototype or a bridge to production. The non-recurring cost is high, but it buys a proven design and a fixture you can reuse. Treat the first run as an engineering cost, not a production price.
The number to track is the recurring unit cost. If it drops 40% at 100 pieces and another 15% at 1,000 pieces, the table has done its job. If it barely moves, the part is dominated by machine time and material, and volume will not save you.
What documentation should come with the parts?
At minimum, a material certificate traceable to the heat number and a dimensional inspection report. For regulated industries, add first article inspection reports and process capability data on the critical features. These are billable lines, so put them in the table before the order, not after.
Every GreatLight order runs 100% inspection before shipment, covering raw material check, in-process monitoring and final inspection. Reports are available on request, and NDA terms can be signed before drawings are shared.
When is a CNC cost accounting table the wrong tool?
When the part is still changing. If the design is not frozen, the table is a snapshot of a moving target and the numbers mislead. Fix the geometry first, then price it.
It is also a weak tool for one-off repair work where the operation is defined by the machine setup, not by a part number. There, an hourly rate plus a time estimate is more honest than a per-part table.
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