Sheet Metal or CNC Machining: Picking the Process
Sheet metal or CNC machining for a bracket or housing? Uniform walls and bends point to sheet; pockets, bores and thick sections point to the mill.
A bracket can usually be made two ways: cut and bent from flat stock, or machined from a block. Choosing sheet metal or CNC machining early saves a redesign later, and the geometry usually makes the call for you.
When Does CNC Machining Beat Sheet Metal for a Part?
When the part needs things a flat sheet can't give it: pockets, bores, thick or varying sections, or real 3D shapes. If the part is a uniform wall with bends and holes, sheet metal is usually the better fit.
Protocase asks this in their Proto Tech Tip When CNC Machining Beats Sheet Metal Fabrication (5 Situations). The description lists the cases: tight tolerances, "deep pockets, internal cavities, and intricate 3D shapes," thick materials and surface finish needs.
Sheet Metal or CNC Machining: How to Tell From the Model
Sheet metal fits when every wall is the same thickness and the shape comes from bends. Our sheet metal analysis reads the flat pattern, bend count, bend angles and inner radii from the model, and PEM insertion is costed as its own line item. See what PEM hardware is for that trade.
Machining fits when the part has a bore that locates something, a pocket, a boss or a sealing face. Our CNC standard is "ISO 2768-m standard, down to ±0.01 mm", while sheet metal is "±0.13 mm cut, ±0.5° bend angle". If a feature needs a fit, that difference decides it.
Cost follows material use. Protolabs' guide to manufacturing methods for enclosures says machining "is somewhat more expensive" because it cuts the part from a block, and that "For orders of 150 or more parts, going with sheet metal fabrication or injection molding may be cheaper in the long run." Machined enclosures there are mostly one-offs and prototypes.
What About Doing Both?
Plenty of good assemblies do. A bent bracket carries the load, and a small machined block bolts on where something has to locate accurately. You only pay for machining where it matters.
Material choice is similar across both. Aluminum 6061, Stainless 304 and Stainless 316 are on our Materials page for CNC and for sheet. Sheet also has Aluminum 5052, Cold Rolled Steel and Galvanized Steel. If you're between gauges, choosing sheet metal thickness helps. For a printed option on small runs, see 3D printing or sheet metal for PCB enclosures.
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