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If you are developing a plastic part and need anywhere from a few dozen to a few thousand pieces, you will face a classic manufacturing question: should you choose low volume CNC machining or invest in injection molding? Pick the wrong process and you either overpay on every part, or spend tens of thousands of dollars on a mold for a design that is still changing. This guide gives you a practical framework — with real cost logic — to make the right call.
The short answer: Below roughly 500 pieces, CNC machining almost always wins on total cost because there is no tooling investment. Between 500 and 5,000 pieces, calculate your crossover point (formula below). Above 5,000 identical parts with a stable design, injection molding usually delivers the lowest unit cost.
The two processes are fundamentally different. CNC machining cuts your part out of a solid block of material, while injection molding forces molten plastic into a shaped steel cavity. Every practical difference — cost, speed, tolerance, design freedom — follows from that fact.
| Factor | Low Volume CNC Machining | Injection Molding |
|---|---|---|
| Tooling cost | None | Typically $3,000 – $50,000+ per mold |
| Unit cost (simple plastic part) | Roughly $15 – $80 per piece | Can fall below $1 – $5 at volume |
| Best volume range | 1 – 5,000 pieces | 1,000 – 1,000,000+ pieces |
| First-part lead time | About 5 – 7 working days | 4 – 8 weeks (mold must be built first) |
| Typical tolerance | ±0.02 mm standard; tighter on request | ±0.05 – 0.1 mm at best |
| Materials | Almost any metal or engineering plastic | Moldable thermoplastics and some thermosets |
| Design changes | Edit the CAD file, run the next part | Modify or remake the mold ($2,000 – $20,000 per revision) |
| Geometry limits | Cutting tool must reach the feature | Needs draft angles, uniform walls, managed undercuts |
The decision is mostly arithmetic. Injection molding carries a large fixed cost (the mold) and a tiny unit cost. CNC machining carries no fixed cost and a higher unit cost. The crossover quantity is the point where the two total-cost lines meet:
A worked example: suppose your ABS enclosure quotes at $38 per piece machined and $1.80 per piece molded, with a $12,000 mold. The crossover is $12,000 ÷ ($38 − $1.80) ≈ 331 pieces. If your lifetime volume is 200 pieces, machining is cheaper. If it is 3,000 pieces, molding saves you well over $90,000 across the product life. Ask your supplier to quote both processes so you can run this calculation with real numbers instead of rules of thumb.
Be honest about demand, including spare parts. Below about 500 pieces, tooling rarely amortizes and machining wins regardless of part complexity. Between 500 and 5,000, run the crossover formula. Above 5,000, molding nearly always wins on cost — unless the next questions say otherwise.
This is the question teams get wrong most often. With CNC machining, a design revision costs you nothing but the next part. With injection molding, every revision means mold modification or a new mold. If you are still in engineering validation, user testing, or regulatory review, machine your parts until the design is locked.
Bearing seats, press fits, O-ring grooves, and sealing surfaces often demand ±0.02 mm or tighter. CNC machining holds that routinely — at ANOK, tolerances down to ±0.002 mm are achievable on critical features. Injection molding typically holds ±0.05 to ±0.1 mm, and pushing tighter requires premium tooling and tight process control. If precision drives your design, machining stays attractive even at higher volumes.
Machined parts ship in days. Molded parts wait weeks while the tool is cut, trialed, and corrected. If you have a trade show, a pilot installation, or a customer trial inside a month, precision CNC machining is the only realistic route.
Molded parts need uniform wall thickness (typically 0.5 – 3 mm), draft angles of 1° – 3°, and careful handling of undercuts. Snap fits, living hinges, and thin ribs are cheap to mold but painful to machine. Deep pockets, sharp internal corners, and thick sections machine easily but cause sink and warpage in a mold. A good supplier will flag these issues in a DFM review before you commit either way.
Even in the same nominal material, a machined part and a molded part behave differently. A machined part is cut from solid stock, so it keeps the full, isotropic strength of the raw material. A molded part contains flow orientation, possible weld lines, and molded-in stress, and its wall sections cool at different rates. For visual and fit checks this rarely matters. For load-bearing, pressure, or fatigue applications, validate the molded version on its own merits rather than assuming the machined prototype's test results carry over.
A related trap is material grade selection: the ABS or nylon you machine from rod stock is not the same formulation as the injection molding pellet grade. When you prototype by plastic CNC machining, choose a stock grade whose properties closely match your intended molding resin, and confirm the match with your supplier's engineering team.
For most products, the lowest-risk strategy is not choosing one process — it is sequencing both:
This path works best when one supplier runs both processes under one roof, because dimensional consistency between the machined bridge parts and the molded production parts is verified within a single quality system.
ANOK Precision Manufacturing is an ISO 9001:2015 certified factory in Shenzhen, China, founded in 2007, offering CNC milling (3-, 4-, and 5-axis), CNC turning, surface grinding, wire EDM, and injection molding services. The shop machines the full range of engineering plastics — ABS, POM, nylon, PC, PEEK, PTFE, and more — as well as aluminum, stainless steel, brass, and titanium, with tolerances down to ±0.002 mm and surface finishes to Ra 0.2.
Because ANOK provides both machining and molding, its engineers can quote your part both ways, run the crossover analysis at your expected volume, and manage the prototype-to-production transition as one project. DFM feedback before production helps catch wall-thickness, draft, and tolerance issues early, whichever process you choose.
There is no universal number — compute it: mold cost ÷ (CNC unit price − molded unit price). For simple parts with inexpensive molds the crossover can be near 300 pieces; for complex parts with premium multi-cavity molds it can exceed 1,500 pieces.
Yes — this is standard practice. Just remember that machined parts are free of weld lines and flow stress, so treat molded-part validation as its own step for structural applications.
Injection molding does not apply to metals; the high-volume alternative is die casting, which carries even higher tooling cost and looser as-cast tolerance. Below a few thousand metal parts per year, CNC machining is almost always the economical choice.
Not sure which process fits your project? Send ANOK your 3D model and target volume — you will get a dual quote for CNC machining and injection molding with a clear crossover analysis. Contact our engineering team today.