Sheet metal has an image problem. Say the words and most people picture a gray electrical box with visible screws, a sticker for a label, and corners that do not quite meet. But the same process — cut a blank, bend it, join it, finish it — also produces high-end audio equipment, laboratory instruments that look like they cost what they cost, and appliance panels people run a hand along in a showroom. The difference is a set of decisions that cost nothing at the drawing stage and are impossible to fix once parts exist.
Why sheet metal is worth designing well
From a handful of units to a few thousand, bent sheet metal beats molded plastic on almost every axis except one. There is no tooling cost — you pay for programming and setup, not a $30,000 mold. Lead times are days to weeks, and a design change is a new flat pattern. It carries structural load, shields EMI, sinks heat, and communicates quality by weight. The one thing it cannot do is compound curvature, which is what plastic is for. The manufacturing rules are in the sheet metal design guide.
Corners are the whole game
Nothing separates a designed sheet metal product from a fabricated one more than the corners. Four treatments are common and they read very differently.
- Open corner. Two flanges bent up, meeting with a visible gap. Cheapest, weakest, and it announces itself as a box. Fine inside a chassis, not on a visible face.
- Overlapped or tabbed corner. One flange laps over the other, often with a tab into a slot. Stronger and self-locating for assembly, but there is a visible step.
- Welded and ground corner. Seam welded, then ground and polished flush — a continuous surface with no visible joint, which is what premium enclosures do. Expect $15–$60 per corner and plan for weld distortion.
- Mitered and folded corner. The blank is coined on the inside so the corner folds closed on itself. A sharper external radius than a normal bend allows, and very clean when the shop has the tooling.
Bends also have a visible inside radius, and a designer who lets the CAD pick radii ends up with three different ones on a single product for no reason. Pick one bend radius — usually equal to material thickness — and use it everywhere on visible surfaces. Consistency reads as intent.
Hide the fasteners
Visible screw heads on a front face are the fastest way to make a product look like equipment. Options, roughly by cost:
- Move them to the back or bottom. Free, but it costs a rethink of the assembly sequence, which is why it gets skipped.
- Self-clinching hardware. Nuts and standoffs pressed in from the hidden side, so the visible surface stays flat and the screw comes from behind. This should be the default.
- Tabs and slots. A folded panel captured in slots and retained by one hidden screw.
- Magnets or captive quarter-turn latches for service panels that open often.
- Countersunk screws where a fastener must show — then make it deliberate, with matched finish, aligned drive slots, and even spacing.
Gaps, seams, and alignment
Perceived quality in metal is mostly gap consistency. A 1 mm gap that is 1 mm everywhere looks precise; a gap running 0.5 mm at one end and 2 mm at the other looks broken, even though it is tighter on average. Bend tolerances are real — roughly ±0.5 mm on location and ±1 degree on angle, accumulating across every bend — so design gaps large enough to absorb the stack, then hold them uniform.
Tactics: put the seam where a shadow line already exists; use a recessed reveal instead of a flush joint, because a deliberate 2 mm groove hides tolerance that a 0.3 mm flush joint cannot; and locate mating panels off shared datums so errors do not compound. Running the numbers first is a straightforward tolerance stack-up analysis.
Material, grain, and finish
| Material | Finish options | Notes |
|---|---|---|
| Cold rolled steel | Powder, wet paint, plating | Cheapest, strongest, heaviest; rusts bare |
| Aluminum 5052 | Powder, dull anodize, paint | Best formability; anodizes less cleanly than 6061 |
| Aluminum 6061 | Anodize, powder, brush | Cracks at tight bends; use generous radii |
| Stainless 304 | Brushed, bead blast, mirror | Expensive, springs back hard, shows fingerprints |
Grain direction is the detail nobody expects. Brushed stainless and brushed aluminum have a directional finish, and if two adjacent panels have grain running different ways the product looks assembled from spare parts. Specify grain direction on the drawing for every visible surface and orient the flat patterns accordingly — it occasionally costs material yield and is always worth it.
The two mainstream finishes behave differently. Powder coating is durable and slightly soft-edged; it fills small scratches and hides minor weld grinding, and textured powders hide a great deal. Wet paint gives finer control of gloss and a thinner build, which matters where two parts fit closely — see powder coating versus wet paint. For aluminum, anodizing keeps metal reading as metal, and Type II in a mid-tone color is one of the best value finishes in hardware — but never anodize two mating parts in different alloys and expect them to match.
Welds and cut edges
Welding distorts thin sheet, so long unsupported seams on a visible panel show waviness under raking light; break the surface with a bead or a reveal, or spot weld a hidden seam. Cut edges have character too — laser leaves a matte heat-affected edge, waterjet a sandblasted texture, punching a rollover and a burr. Specify the process for edges people touch; the differences are in plasma versus laser cutting.
Prototype in the real material
Cardboard and printed mockups get proportion right and metal completely wrong. Springback, edge sharpness, panel resonance when tapped, and the way light travels across a brushed face only exist in the real material. A one-off sheet metal prototype typically costs $200–$1,500 and takes one to two weeks, and it changes decisions — usually about gaps and radii — that would otherwise ship. For an enclosure, compare the folded approach against extruded and machined aluminum enclosures first.
Finally, treat color, texture, and finish as a designed set. A bead-blast panel against a brushed bezel and a soft-touch handle is a composition, best decided together — the discipline in CMF design.
Projects House designs sheet metal products where the metal is the product — corner and seam strategy, hidden fastening, finish specification, and fabrication drawings your shop can quote without a phone call. Send your concept through our contact form.