Buyers who come to me for metal springs, CNC turned parts, precision metal stamping, PP injection moulding, or aluminum precision machining almost always ask the same question: "Which CNC parts manufacturer should I use?" And every time, I give them the same answer: it depends.
That's not a cop-out. I'm a quality and compliance manager. I review components before they reach customers—hundreds of parts daily, roughly 8,000 to 10,000 items a year. In 2024 alone, I rejected about 12% of first deliveries due to out-of-tolerance dimensions, inconsistent surface finishes, or material certifications that didn't match what was ordered. A good chunk of those rejections trace back to choosing the wrong process at the start.
So instead of giving you a one-size-fits-all answer, here's a decision tree. Find the scenario that matches your situation.
Start With the Baseline Numbers
Before you compare any quotes, you need these cost benchmarks. These come from publicly listed supplier quotes and my own vendor comparisons across dozens of projects in 2024. Prices are as of January 2025—verify current rates.
- Precision metal stamping tooling: $2,000–$20,000 depending on complexity and tolerance
- PP injection moulding tooling: $5,000–$50,000+ depending on cavity count and surface finish
- CNC setup fees: typically $50–$500 for programming and first-article inspection
- Standard CNC turned parts: $1–$15 per piece at 1,000 units
- Aluminum precision machining: $5–$50 per piece for moderate complexity
These are reference points, not quotes. The real number depends on your geometry, material, tolerances, and the supplier you pick. (Should mention: setup fees and tooling costs are where most buyers get surprised—they focus on unit price and miss the rest.)
What actually determines which process and supplier make sense for you? Four things: your volume, your part geometry, your tolerance requirements, and whether you need multiple part categories from one source.
Scenario A: Prototyping or Low Volume (1–500 Pieces)
You're still validating the design. You need parts, but you're not ready to drop thousands on tooling.
For CNC turned parts and aluminum precision machining, this is CNC machining territory. Setup is cheap, changes are easy, and there's no tooling investment. You can iterate on the design without waiting weeks for a new mould.
For metal springs—honestly, unless your design is truly unusual, buy stock springs. Custom spring winding carries a setup cost of $200–$500, and at low quantities, that never amortizes well. I learned this the hard way in 2023 when we ordered 200 custom compression springs for a prototype. The springs cost $4 each. The setup cost $400. Total per-piece: $6. The stock equivalent would've been $2.50 each, and we could've had them in three days instead of three weeks.
Counterintuitive advice: At this volume, don't chase the lowest unit price. Ask about setup fees, minimum order quantities, and expedite charges. I've seen quotes at $3 per piece with a $500 "engineering fee" tacked on—making the first order $13 per piece. That's the unit-price trap.
Here's my rule: under 500 pieces, you're paying for setup. Find suppliers who are transparent about it, not ones who hide it in per-piece pricing.
Scenario B: Mid Volume (500–10,000 Pieces)
This is where it gets interesting. The right answer depends entirely on your part geometry.
For simple round parts—shafts, spacers, bushings—CNC turned parts stay competitive well into the thousands. The tooling is just a program, so design changes don't add weeks or thousands of dollars.
But if you're making flat or thin-walled parts, precision metal stamping starts to pay off around 5,000 pieces. Tooling might run $3,000–$8,000, but per-piece pricing drops to $0.10–$1.00. The math shifts fast.
PP injection moulding at this volume? Honestly, for most projects, it's not worth it yet. Unless the part is extremely simple, tooling is $8,000–$15,000 and per-piece lands around $1–$3. Your total cost often comes out similar to CNC machining—but with less flexibility and a longer lead time.
The surprise isn't the tooling cost. It's that a part you thought was "high volume" isn't actually high volume enough to justify the tool.
Here's what I see go wrong: buyers hit "production mode" and immediately default to stamping or injection moulding without running the numbers. Then the stamping quote comes back higher per piece than the CNC quote—because the geometry requires a progressive die, and progressive dies aren't cheap. I watched a buyer approve a $12,000 stamping tool for a part where CNC turning would've been cheaper per piece until 15,000 units.
Scenario C: High Volume (10,000–100,000+ Pieces)
Now you're in dedicated tooling territory. Precision metal stamping and PP injection moulding come into their own.
Typical numbers at 10,000 pieces:
- Stamping tooling amortized per piece: $0.30–$0.80
- Injection moulded part cost: $0.50–$2.00 (depending on size and cavitation)
- CNC machining per piece: $3–$20 (at 10,000 units)
The gap is clear. But the catch: you need stable, long-term demand. Once tooling is cut, you're locked to that supplier. Switching means transferring the tool—or paying to cut a new one.
For metal springs, this is also where custom winding makes financial sense. The setup cost gets spread across enough units that the per-piece price becomes reasonable. At 100,000 units, a custom spring might cost $0.15–$0.40 each, versus $2–$4 for a CNC-machined equivalent.
Scenario D: You Need Multiple Part Categories
This is where procurement gets complicated. Say you need an assembly that includes metal springs, CNC turned parts, and precision metal stamping.
You have three paths:
- Source each category from a specialist supplier
- Find a single CNC parts manufacturer who can handle multiple processes
- Use a lead supplier who manages subcontractors
In my experience managing a 50,000-unit annual order, we tested path two—consolidating everything with one supplier. It worked for the easy parts. We hit problems with the injection moulded components, where tolerances drifted outside our spec after the first 5,000 units. It took six weeks to resolve. Six weeks we didn't have.
My take: if tolerances are tight—say ±0.05mm or better—use a specialist for that category. If tolerances are looser, a multi-process supplier can save you serious coordination time.
The frustration was real: we thought consolidation would simplify things. It didn't. It just moved the complexity from vendor management to problem diagnosis.
How to Figure Out Which Scenario You're In
Ask yourself five questions:
- What's my annual volume? Under 500 pieces = Scenario A. 500–10,000 = Scenario B. 10,000+ = Scenario C.
- What shape is my part? Flat and thin = stamping. Round and cylindrical = turning. Complex 3D = CNC machining. Plastic = injection moulding.
- Is my long-term demand stable? If it fluctuates wildly, avoid tooling-based processes. Stay with CNC machining and its inherent flexibility.
- How tight are my tolerances? Very tight tolerances require specialists, regardless of volume.
- Am I sourcing multiple part categories? If yes, Scenario D applies. Decide whether to consolidate or specialize.
There's no universal answer. But if you run the setup costs, per-piece prices, and annual volumes, the right path usually reveals itself.
One last thing: in my experience, the lowest unit price is rarely the lowest total cost. I made that mistake on an aluminum precision machining project in 2023. Picked the lowest quote—$4.20 per piece. The first article failed inspection. We spent three weeks on rework and expedited shipping. Final cost per piece: $5.90. The second-lowest quote had been $4.80.
That $0.60 difference per piece would've saved us three weeks and about $1,200 in expedite fees. Instead, we paid more and lost time. (Oh, and the vendor's "generous" offer to rework at 50% off? Still made them more expensive than their competitor.)
So before you pick a CNC parts manufacturer, ask not "who's cheapest" but "who's cheapest after setup, tooling, rework risk, and lead time." That's the number that actually matters.