CNC 加工コスト削減：2026 年版インサイダーガイド（実数値）

Anatomy of a CNC quote — where the money actually goes

Before you can reduce cost, you need to know what you’re paying for. A typical CNC quote breaks down roughly like this for a small-to-medium aluminium part at batch 100:

The design lever: 15-40% achievable savings

Design changes have the biggest impact because they reduce machine time directly. Every minute saved on cycle time is locked-in savings across every unit you’ll ever make.

1. Increase internal corner radii to ≥ 1 mm — uses larger, faster end mills. Saves 5–15% on cycle time.
2. Avoid pockets deeper than 4× tool diameter — long tools chatter and require finishing passes. Re-design to 3× saves 10–20%.
3. Consolidate features onto fewer faces — every additional face adds a setup. Reducing from 4 setups to 2 saves 20–30%.
4. Standardise hole sizes — pick metric (M3, M4, M5, M6, M8) or imperial standards. Avoids tool changes and special drills. Saves 3–5%.
5. Avoid sharp external corners — add 0.3 mm chamfers. Eliminates deburring labour. Saves 2–5%.
6. Minimum wall thickness ≥ 1 mm metals, 1.5 mm plastics — thinner walls deflect, requiring lighter cuts and more passes. Saves 5–10%.
7. Match thread depth to 1.5× thread diameter — anything deeper is wasted cut time. Saves 1–3%.
8. Use standard fastener clearance holes — drilled in one pass with off-the-shelf drills. Avoid “between size” holes that need reaming.
9. Specify symmetric features where possible — symmetric parts can be machined with simpler fixturing.
10. Avoid unnecessary undercuts — undercuts require T-slot cutters and slow cycles. If unavoidable, design for a standard 6 mm slot.

The material lever: 10-30% achievable savings

Material is 15–35% of the total cost. Switching from a premium alloy to a standard one — when the application allows it — is among the fastest single-change savings.

The tolerance lever: 10-20% achievable savings

Tolerances drive cost more than people realise. Pulling tolerances back from blanket ±0.025 mm to ISO 2768-mK default (±0.1 mm for non-critical features) reliably saves 10–20% on most parts.

1. 1

   Audit your drawing for default tolerances

   If you don’t have a general-tolerance call-out (ISO 2768-mK or ASME equivalent), every dimension defaults to whatever the shop assumes — usually conservative and expensive.

2. 2

   Identify only the critical features

   Mating diameters, sealing faces, bearing seats, datums. Usually 3–8 features per part actually need tight tolerance.

3. 3

   Tighten only those

   Leave the rest at default. The 80/20 rule: 20% of features drive 80% of inspection time and cost.

4. 4

   Specify surface finish only where it matters

   Default to Ra 3.2 µm. Tighten to Ra 1.6 or Ra 0.8 only on sealing or sliding surfaces.

The finish lever: 5-15% achievable savings

Surface finish costs are often the easiest to optimise because the function/cost trade-off is direct: most finishes are independent and can be relaxed without affecting machining.

• Replace hard chrome with electroless nickel — comparable wear protection, ~30% cheaper, ENVL-friendlier (hexavalent chrome being phased out).
• Type II anodise instead of Type III — if hardness isn’t required. Savings: ~40%.
• Bead blast then anodise rather than polish-then-anodise. The matte finish is more forgiving and cheaper. Savings: ~50% on finishing.
• Single-batch processing — for small orders, asking the shop to process all units in a single anodise/plate batch saves setup costs. ~10% savings.
• Skip the colour — natural aluminium anodise (clear) is cheaper than coloured. Black is the cheapest colour.
• Powder coat instead of wet paint for industrial parts where exact colour match isn’t required. ~20% cheaper at volume.

Full breakdown in our surface finishing guide.

Volume crossover: when does it actually pay to order more?

Per-unit cost drops dramatically with volume — but the curve flattens. Knowing the crossover points helps you batch orders intelligently.

The supplier lever: 5-30% achievable savings

• Bypass marketplace middlemen — RapidDirect, Xometry, Protolabs and similar marketplaces charge 20–40% above the actual machine shop. They add value (DFM, vetting, payment terms) but the markup is real. For repeat work, going direct to the shop captures most of that.
• Send the same RFQ to 3–5 shops — pricing varies surprisingly widely on the same drawing. Don’t commit until you’ve compared at least three quotes.
• Ask shops to quote alternative materials — a good supplier will suggest a cheaper alloy if the application allows. Bad ones quote exactly what you asked.
• Pay on delivery, not on order — improves your working capital and gives the shop a quality incentive (they don’t get paid until you accept).
• Build a long-term relationship — preferred customers get priority scheduling, sometimes lower margins, and proactive cost-saving suggestions.
• For high-tolerance / low-volume work, choose specialists over generalists — a shop that does aerospace daily will quote that part better than one that mainly does brackets.

Priority stack: what to do first

If you can’t do everything, do these in order:

1. 1

   1. Add ISO 2768-mK to the title block (free, 5 minutes, 5–15% saving)

   No design changes, no risk. Just adds a sane default tolerance to the drawing. Sometimes the fastest single line you’ll ever add.

2. 2

   2. Audit material spec (5 min review, 10–30% potential saving)

   Confirm the alloy is functionally required, not historical. Switch to a more economical alloy where the application allows.

3. 3

   3. Run a DFM review (1 hour, 10–25% saving)

   Submit CAD for review. Apply suggested radius and geometry tweaks.

4. 4

   4. Re-quote at 2–3× volume (free, 15–40% per-unit saving)

   See if combining future projected demand into one larger order brings the unit cost down enough to be worth it. Use blanket-order release.

5. 5

   5. Compare 3–5 supplier quotes (1 day, 5–25% saving)

   Make sure you’re paying market rate, not a marketplace markup.

6. 6

   6. Optimise finish spec (1 hour, 5–15% saving)

   Match finish to actual function. Drop unnecessary cosmetic specs.

Hidden costs people miss

• Setup time on small batches. For batch ≤ 10, setup can be 50% of total cost. Combine designs into a single setup if possible.
• Rush fees. Asking for 50% lead-time reduction typically costs 30–50% more. Plan ahead.
• Inspection time on tight tolerances. ±0.005 mm parts can require 20–40% of total time in inspection alone.
• Scrap rate at tight tolerances. 5–15% scrap at ±0.005 mm. The cost gets distributed across surviving units.
• International shipping for low-value high-weight parts. A $50 stainless bracket shipped from China by air can cost $80 in freight.
• Custom packaging. Foam-fitted boxes and individually wrapped parts add 5–15%.
• Documentation premium. AS9100/ISO 13485 certified work adds 25–50% over standard ISO 9001 — see our DFM + aerospace/medical guide.
• Currency hedging. Parts quoted in USD vs RMB can swing 5–10% over a 6-month delivery cycle.