The Main Functions of CNC Milling Costs: A Buyer's Checklist
A quote for a milled part is not one number. It is a stack of machine functions, setup decisions and inspection steps, each with its own cost line. This guide is written for engineers and sourcing teams who need to read that stack and compare suppliers on equal terms.
In this article
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Key takeaways
How each milling function moves the quote
Typical effect on unit price for a 50-piece run.
| Function | What it does | Cost effect | Watch out for |
|---|---|---|---|
| Point control | Drills and taps at set coordinates | Low | Hole-to-hole position error |
| Contour interpolation | Lines, arcs, non-circular curves | Medium to high | Short CAM cycles, chatter |
| Tool radius compensation | One program, many cutter sizes | Lowers cost | Wrong offset direction |
| Tool length compensation | Keeps Z aligned after tool change | Lowers cost | Unmeasured tool length |
| Scale and mirror | Symmetrical or scaled features | Lowers cost | Mirrored threads, handed features |
| Rotation | Program runs at any table angle | Lowers cost | Fixture clearance |
| 5-axis simultaneous | One setup, compound angles | High, then drops | Programming hours at low volume |
The short version
Price the functions your part actually uses, and compare suppliers at the same tolerance, material grade and setup count. Anything else is guesswork.
Why the functions of CNC milling costs are not one number
When a shop sends a price for a milled part, that number is the sum of several machine functions working together. Point control places holes. Contour control cuts the profile. Compensation functions keep the cutter on the intended path after a tool change. Each one adds or removes time from the cycle, and time is what you pay for.
This matters when you compare suppliers. Two quotes can differ by 40% and still be correct, because one shop is pricing a 3-axis job with a simple fixture and the other is pricing the same part on a 5-axis center to avoid a second setup.
The useful question is not which number is lower. It is which functions the shop plans to use, and whether that plan fits your tolerance, volume and deadline. A quote that never names the machine or the setup is a quote you cannot compare.
- 1Time is the unitEvery function either adds cycle time or removes a setup, and both change the price.
- 2Volume changes the winnerAt 1 piece, setup dominates. At 10,000 pieces, cycle time dominates.
- 3Tolerance multiplies the workTight true position needs better fixturing, slower feeds and more inspection.
Point control and contour control: the two cost extremes
Point control is the cheapest milling function to run. The machine moves to X, Y and Z, drills or taps, and moves on. Cost is driven by hole count and position tolerance, not by shape. A plate with 60 holes at ±0.1 mm is fast. The same plate at ±0.02 mm true position needs a probe check and a more rigid setup.
Contour control is the other end. The control interpolates straight lines, arcs and non-circular curves, so the cutter follows a path instead of a point. Long 3D surfaces mean short CAM segments, and short segments mean the machine never reaches full feed. Cycle time grows faster than the part looks.
A practical rule: if a feature can be made with a drill or a tap, keep it as point control. If it needs a swept surface, expect contour pricing. Mixing the two on one part is normal, but the quote should show where the time goes.
- 1Point controlHoles, tapped holes, counterbores. Cheapest per feature.
- 2Contour controlProfiles, pockets, arcs, 3D surfaces. Price scales with path length.
- 3Hard materials slow both316L, Ti-6Al-4V and Inconel cut at lower feeds, so both functions cost more.
Compensation and transformation functions that cut cost
Tool radius compensation lets the control shift the cutter path by the actual radius of the tool in the spindle. The programmer writes the part geometry once. If the cutter wears or the shop swaps in a different diameter, the operator changes an offset value instead of the program. On a job with several pocket sizes, this removes hours of CAM work.
Tool length compensation does the same in Z. After a tool change, the control adds the measured length so the tip lands where the program expects. Skip this and the first cut after every change is a scrap risk. Shops that measure tools offline and load the values automatically run tighter and cheaper.
Scale, mirror and rotation functions go further. Mirror lets one program cut a left and right hand of the same bracket. Rotation lets the program run at an angle set on a rotary table, so a compound-angle hole can be milled in one setup instead of two. All three reduce programming and fixturing, which is where small runs lose money.
- 1Radius offsetOne program, many cutter sizes, less reprogramming.
- 2Length offsetKeeps Z true after tool changes, protects the first cut.
- 3MirrorLeft and right parts from one program. Check threads and handed features.
- 4RotationCompound angles with fewer setups. Confirm fixture clearance.
Judging a supplier on functions, not just price
Once you know which functions your part needs, you can ask better questions. Does the shop have the travel to cut it in one setup? For a long housing, 4,000 × 400 × 150 mm travel means no repositioning. For a compact manifold, a 500 × 500 × 450 mm machine is enough and usually cheaper per hour.
Ask how the shop holds tolerance. A ±0.005 mm claim is only credible with in-process monitoring and a final inspection report. At GreatLight, parts are inspected 100% before shipment, with raw material checks up front and reports on request.
Certifications matter when your part feeds a regulated line. ISO 9001:2015 covers general quality. IATF 16949:2016 fits automotive. ISO 13485:2016 fits medical. ISO 27001:2022 covers how your files are handled. A shop with the right scope will say which applies to your job, not list all four for show.
- 1Machine travelMatch the machine to the part envelope to avoid repositioning.
- 2Inspection planWho checks what, at which step, with which instrument.
- 3Certification scopeThe relevant certificate should name the process and the site.
How to scope a milling quote in 6 steps
Run this before you send an RFQ.
- 11. Split features into point and contourList holes, taps and bores separately from profiles and surfaces. This shows where the cycle time will sit.
- 22. Set one tolerance band per featureUse ±0.1 mm for clearance holes, ±0.02 mm for fits, ±0.005 mm only where the design needs it. Tightening everything raises the price with no gain.
- 33. Count the setupsIf the part needs 4 faces, ask whether a 5-axis center can do it in one. Fewer setups means less fixture and less position error.
- 44. Name the material and temper6061-T6, 316L, 17-4PH and Ti-6Al-4V all cut differently. The grade, not just the family, sets the feed rate.
- 55. Specify finish as a rangeRa 1.6–3.2 μm as-machined, Ra 0.8–1.6 μm for sealing faces, Ra 0.2–0.8 μm only when the drawing calls it out.
- 66. Ask for a line-item quoteProgramming, setup, cycle time, finishing and inspection should each appear. A single lump sum hides the functions you are paying for.
Common questions
Why do two shops quote the same part so differently?
They are pricing different functions. One may plan a 3-axis job with two fixtures, the other a 5-axis job with one setup and more programming hours.
Ask each shop to list the machine, the setup count and the inspection step. Once those match, the numbers usually get close.
Does a tighter tolerance always cost more?
It costs more only when it forces a change. Below about ±0.02 mm, shops need better fixturing, slower passes and more probing, so the price rises.
If a feature is a clearance hole, holding ±0.1 mm costs less and works the same.
Is 5-axis always the expensive option?
Not at volume. At low volume the programming hours dominate. At a few hundred pieces, one 5-axis setup often beats three 3-axis setups because fixture cost and position error drop.
For a part with faces on four sides, ask for both quotes and compare total cost.
How does material grade affect the quote?
It sets the cutting speed. Aluminium 6061-T6 cuts fast. Stainless 316L, 17-4PH and Ti-6Al-4V cut at lower feeds and need more tool changes.
Harder grades also wear cutters faster, so tool cost appears in the cycle time line.
What should be in a milling quote besides the unit price?
Programming, setup, cycle time, surface finishing and inspection. Also the material cost with the grade named.
If the quote includes an inspection report, confirm which features are measured and at which step.
Can I start with one piece?
Yes. GreatLight has no minimum order quantity and runs from one prototype to 10,000+ part runs.
Quotation and free DFM analysis come back within 12 hours, and production can start within 24 hours.
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