Choose sheet metal when your part is a thin-walled enclosure, bracket, panel or chassis with a single wall thickness — it is typically 3-8 times cheaper per part than machining the same volume from solid billet and ships in 3-7 working days. Choose CNC machining when you need wall thickness above about 6 mm, tolerances tighter than ±0.1 mm, threaded blind holes, or 3D features such as pockets, bosses and contoured sealing faces.
Where each process wins
- Sheet metal: enclosures, chassis, brackets, panels, covers, racks — 0.5-6 mm wall
- CNC machining: heat sinks, precision fixtures, manifolds, thick-walled housings, parts with milled pockets
- Sheet metal: flat-pattern parts that unfold — every feature reachable by laser and brake
- CNC machining: features on multiple faces at tight relative position, or deep blind cavities
- Both: hybrid — laser-cut blank, then machine critical interfaces and tapped holes
Cost: why milling a box from billet is expensive
Machining an enclosure from solid removes 70-90% of the material as chips and pays for that removal in cycle time. A laser-cut and folded box uses nearly all the stock and forms in minutes. At 1-50 pieces the gap is usually 3-8x; it widens with size because a bigger machined envelope means more air-cutting. Machining becomes competitive again when the part needs features sheet metal cannot form, or when a single machined part replaces a welded assembly of six.
Tolerance is the real dividing line
Sheet metal bending holds roughly ±0.1-0.3 mm per flange and accumulates across a chain of bends; laser-cut hole positions land around ±0.1 mm. CNC machining holds ±0.02-0.05 mm standard and ±0.005 mm on precision features. If your enclosure just needs to close and carry connectors, sheet metal is fine and cheaper. If a bore must align with a shaft across the box, either machine the feature into the formed part or design a machined sub-plate that carries the precision.
Design constraints to check before you choose
- One thickness per part: a bent sheet metal part cannot have stepped wall sections
- Inside bend radius: design at 1x material thickness to match standard press brake tooling
- Holes near bends: keep 2.5x thickness plus bend radius clear, or they distort
- Deep pockets, tapped blind holes and contoured sealing faces: machining territory
- Finish: powder coating and anodizing suit sheet metal; machined parts also take bead blast and clear anodize
Lead time and volume
SkillsProto laser-cuts, forms and finishes in-house: 3-7 working days for 1-100 pieces, scaling into low-volume production on the same fixtures with no tooling to amortize. Machining runs a similar 1-5 days for prototypes but scales differently — cycle time, not tooling, dominates cost as quantity rises. Above a few hundred enclosures per year, consider a comparison against die casting or a progressive die stamp, both of which we quote alongside.
The hybrid option most teams miss
A laser-cut and formed enclosure with a machined interface plate gives you sheet metal economics where it does not matter and ±0.01 mm where it does — connector seats, bearing blocks, sensor mounts. Send DXF plus STEP and our DFM report will flag every bend radius and hole-distance issue, and price the hybrid option next to the all-machined version.
Frequently Asked Questions
Is sheet metal cheaper than CNC machining for enclosures?
Usually yes — typically 3-8 times cheaper per part for thin-walled enclosures, because laser cutting and folding use nearly all the stock while machining a box from billet removes 70-90% as chips and pays for it in cycle time. The gap narrows when the part needs milled pockets, blind tapped holes or tolerances tighter than ±0.1 mm.
What tolerance can sheet metal fabrication hold?
Expect ±0.1-0.3 mm per bend flange, with tolerance accumulating across multiple bends, and roughly ±0.1 mm on laser-cut hole positions. CNC machining holds ±0.02-0.05 mm standard and ±0.005 mm on precision features. Where an enclosure needs a precision bore, add a machined interface plate rather than tightening the whole fabrication.
When must I use CNC machining instead of sheet metal?
Use machining when wall thickness exceeds about 6 mm, when you need pockets, bosses or contoured sealing faces, when blind tapped holes carry load, or when tolerances must stay inside ±0.1 mm across several datums. Sheet metal also cannot produce stepped thickness in a single formed part.
Can a part combine sheet metal and CNC machining?
Yes, and it is often the most economical answer: laser-cut and form the enclosure, then machine the connector seats, sensor mounts or bearing bores on a secondary operation or a separate machined plate. SkillsProto quotes the hybrid alongside all-sheet-metal and all-machined versions in the same 24-hour DFM response.
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