Flatness is a requirement, not an assumption
Large thin panels are not flat by nature. Coil has residual stress, cutting releases some of it, and any subsequent forming or coating adds more. A 600 mm panel in 1.2 mm steel that reads flat on a bench will show a bow on a painted cabinet.
Where flatness matters, it has to be stated with a value and a method. The usual fixes are a formed edge or a shallow rib on the concealed face, which add stiffness without changing the visible surface — and if the panel is powder coated, coating both faces rather than one keeps the stress balanced.
Hole patterns and datum discipline
A panel with a connector cut-out, a display aperture and a row of fasteners is a pattern, and patterns should be dimensioned from one datum. Chain dimensioning across a panel accumulates every error between the first and the last feature, which is exactly where the tolerance usually fails.
Countersinks add a second consideration: they are depth-controlled, so they belong on a panel whose thickness is confirmed. On a coated panel, the countersink has to accommodate the screw head after coating, which means the panel thickness at the hole changed by the coat.
| Feature | Process | Watch out for |
|---|---|---|
| Outline and apertures | Laser cut or punched | Internal corner radius at least half the kerf |
| Connector cut-outs | Laser cut, to the connector drawing | Dimension from a datum, not by chaining |
| Perforation | Laser cut or punched | Open-area percentage; a perf panel is a weak panel |
| Louvres | Formed or punched | Louvres stiffen the panel but cut airflow hard |
| Countersinks | Machine or punch | Depth versus coated thickness |
| Silk screen or marking | After finishing | Position relative to the finished datum, not the blank |
Finish is visible on a panel
A brushed stainless panel carries a directional grain. It has to be applied consistently and it has to run the same way on every panel in the batch, or two panels side by side on the same machine will look different in daylight. Grain direction also interacts with bending: bending across the grain on a hard temper cracks more readily.
Powder coated panels are judged on colour match and on defects. Rack marks, masking lines and orange peel are all visible on a large flat surface in a way they are not on a folded bracket. If a panel will be inspected under raking light, say so at quotation — it changes which coatings and which racking approach we use.
- State the grain direction on brushed panels, and keep it consistent across the batch.
- For coated panels, specify whether the tolerance applies before or after coating.
- Where a panel is handled and re-handled, agree a protective film or an interleaving requirement.
- Marking (logos, serials, warnings) is positioned off the finished datum.