The CNC vs sheet metal decision usually shows up on brackets, enclosures, mounting plates and chassis parts. Both can produce a part that looks similar in a CAD model, but they reach it in very different ways. Sheet metal cuts and bends thin stock of uniform thickness. CNC machining removes material from a solid block or bar to create varying thickness, pockets, bosses and precise features. The right choice depends on thickness, tolerance, quantity and what the part has to do.
CNC vs Sheet Metal: Comparison Table
Figures are typical and depend on geometry. Cost is a relative per-part index for a bracket-type part, where one machined part at quantity 1 equals 100.
| Factor | CNC machining | Sheet metal fabrication |
|---|---|---|
| Relative cost, qty 1 | 100 | 50 to 70 |
| Relative cost, qty 10 | 40 | 18 to 25 |
| Relative cost, qty 100 | 18 | 7 to 10 |
| Relative cost, qty 1,000 | 10 | 3 to 5 |
| Typical tolerance | ±0.001 to ±0.005 in | ±0.005 in on cut features; ±0.010 to ±0.030 in across bends |
| Surface finish | Ra 32 to 125 µin, controllable | Mill finish sheet, possible bend and tooling marks |
| Materials | Bar, plate and forgings in nearly any alloy | Sheet gauges of steel, stainless, aluminum (often 5052), copper |
| Thickness | Any, with variable wall thickness | Uniform, typically under 0.250 in |
| Lead time | Days to a few weeks | Days to a few weeks |
| Strength and stiffness | Solid sections, high local stiffness, no bend cracking | Stiffness from bends and flanges; efficient for light loads |
| Typical use case | Precision mounts, manifolds, fixtures, bearing housings | Enclosures, covers, panels, simple brackets |
When Sheet Metal Wins
- Thin, uniform parts. Enclosures, covers and brackets under about 1/4 in thick are almost always cheaper as formed sheet.
- Large, light parts. A 24 in enclosure machined from plate would waste most of the material and hours of machine time.
- High volumes of simple shapes. Laser or punch plus a press brake produces parts quickly once the flat pattern is set.
When CNC Machining Wins
- Tight positional tolerances. Hole patterns that must line up within ±0.002 in, or features referenced across multiple faces, are held directly by a machining center rather than stacked through bends.
- Variable thickness and 3D features. Pockets, bosses, counterbores, tapped holes, dowel holes and precision faces all come from one solid part.
- Thick sections and heavy loads. Machined blocks do not have bend radii, springback or cracking at tight bends.
- Precision surfaces. Flatness, parallelism and surface finish callouts are practical on machined parts and difficult on formed ones.
Common Mistakes
- Putting machined-part tolerances on a sheet metal drawing. Bend-to-bend dimensions rarely hold better than ±0.010 in without extra cost.
- Machining a part from plate that is really a bent bracket with two holes. The material and cycle time rarely justify it.
- Specifying inside bend radii smaller than the material thickness, which can crack aluminum and harder tempers.
- Forgetting that a formed part and a machined part need different drawings. Flat patterns, bend reliefs and K-factors do not apply to machining.
Hybrid Designs
Many assemblies combine both. A sheet metal enclosure carries machined mounting blocks, bosses or a precision plate where alignment matters. Keeping the precise features on the machined part and letting the sheet metal handle coverage and structure usually gives the lowest total cost. When a formed part needs one or two precise features, some teams also have a machine shop add bored or reamed holes after forming, provided the part can be fixtured without distortion.
How This Applies at Wexmar
Wexmar does not do sheet metal fabrication, laser cutting or forming. Our work is the machined side: blocks, plates, housings, shafts and turned parts held to drawing tolerances. We mill on six horizontal machining centers with pallet changers, turn on 10 CNC lathes, and inspect on two Brown & Sharpe CMMs. If your assembly mixes sheet metal with precision machined components, we can quote the machined parts and work to the interface dimensions your fabricator uses. See CNC milling, materials we machine, and the related guide on machining vs fabrication.
Getting a Quote
Send the drawing for the machined components and we will quote them with a human review of every line. You can upload a drawing for an instant estimate or call (315) 400-2654, Monday through Friday, 7 to 4 Eastern.