Choosing between CNC machining vs 3D printing comes down to quantity, tolerance, material and how the part is loaded in service. Both processes can deliver a prototype quickly, but they behave very differently once a drawing calls out tight bores, sealing faces, threads or a specific wrought alloy. This guide gives a practical decision framework, the typical tradeoffs, and an honest view of where a precision machine shop fits.
CNC Machining vs 3D Printing: Side-by-Side Comparison
Figures are typical ranges, not guarantees. Cost is a relative per-part index where one machined part at quantity 1 equals 100. Your geometry and material will move these numbers.
| Factor | CNC machining | Polymer 3D printing (SLS, MJF, SLA) | Metal 3D printing (DMLS, SLM) |
|---|---|---|---|
| Relative cost, qty 1 | 100 | 30 to 40 | 200 to 300 |
| Relative cost, qty 10 | 40 | 28 to 35 | 170 to 250 |
| Relative cost, qty 100 | 18 | 25 to 30 | 150 to 220 |
| Relative cost, qty 1,000 | 10 | 22 to 28 | 140 to 200 |
| Typical tolerance | ±0.001 to ±0.005 in; tighter on selected features | ±0.005 to ±0.010 in, or about ±0.3% | ±0.002 to ±0.005 in as built |
| Surface finish | Ra 32 to 125 µin as machined | Ra 125 to 400 µin, visible layers | Ra 200 to 500 µin as built |
| Materials | Nearly any wrought metal or engineered plastic | Nylon, resins, some filled grades | Limited set: 316L, 17-4 PH, Ti-6Al-4V, Inconel 718, AlSi10Mg |
| Lead time | Days to a few weeks | 1 to 5 days | 1 to 3 weeks plus post-processing |
| Strength | Full wrought properties, isotropic | Lower, often anisotropic | Near wrought after stress relief or HIP |
| Typical use case | Functional parts, tight fits, production runs | Form and fit models, complex housings | Internal channels, lattices, consolidated assemblies |
When CNC Machining Wins
- Tight tolerances and fits. Bearing bores, O-ring grooves, press fits and precision threads are held directly by the machine and verified on a CMM.
- Specific alloys and tempers. If the drawing calls for 7075-T651, 316 stainless, Inconel 625 or PEEK, machining starts from certified bar or plate with traceable mill certs.
- Quantities above a handful. Once a program and fixture exist, machined unit cost falls fast. Printing cost per part stays nearly flat because build time scales with volume.
- Fatigue and pressure loads. Wrought material has predictable properties in every direction, which matters for cyclic loads and pressure-containing parts.
When 3D Printing Wins
- Geometry a cutter cannot reach. Internal cooling channels, lattices and closed cavities are the real strength of additive manufacturing.
- Very early concept models. For a quick look at form and fit in plastic, printing is fast and inexpensive.
- Part consolidation. A printed metal part can sometimes replace an assembly of several machined and fastened pieces.
Common Mistakes When Choosing Between CNC and 3D Printing
- Assuming a printed part will hold machined tolerances on bores and threads without secondary machining.
- Qualifying a design with printed prototypes, then switching to machined production and finding the material behaves differently.
- Designing a machined part with deep internal pockets or sharp inside corners that only a printer could make, which drives cost up.
- Ignoring post-processing on metal prints. Support removal, stress relief, HIP and finish machining can double lead time.
Using Both: Printed Near-Net Shapes With Machined Features
A common hybrid is to print a metal part near net shape and then machine the critical features: sealing faces, bearing bores, threads and datum surfaces. This works when the printed part can be fixtured reliably and has enough stock left on the machined surfaces, typically 0.020 to 0.040 in. Early agreement on datums between the print supplier and the machine shop is what makes this approach work.
How This Applies at Wexmar
Wexmar does not do 3D printing. We are a precision CNC machine shop in Canastota, NY, and our work is the machined side of this decision. That includes CNC turning on 10 lathes with live tooling and Y-axis, 3- and 4-axis horizontal milling on six pallet-changing machining centers, and Swiss-type work to 32 mm diameter. Where it is realistic, we also finish-machine printed metal parts supplied by the customer, holding the critical features to drawing and reporting them on our Brown & Sharpe CMMs. See our machine list and the related guide on prototype vs production tolerances.
Getting a Quote
If you are deciding whether to machine or print a part, send the model and drawing and we will tell you plainly whether machining is the right fit. You can upload a drawing for an instant estimate, and a human estimator will confirm every quote. Or call (315) 400-2654, Monday through Friday, 7 to 4 Eastern.