Seven steps from coil to filmed blank, the tolerance each one owns, and why flatness is the number most purchase orders leave out.
A sign blank is made in seven steps: decoil, level, cut to length, punch corners, punch or drill holes, deburr, film. Each step owns one tolerance, and that is the useful way to read a drawing: length and width from the shear, squareness from the stop and the leveller, hole position from the tool, flatness from the leveller and from how the bundle is stacked. If a dimension matters to you, name the step that makes it — the answer is then either a machine capability or a price.
The line is a cut-to-length line with a leveller in front of the shear, followed by a punch press and a film applicator. Coil goes in at one end; stacked, filmed blanks come out at the other. What changes from order to order is coil width, alloy and temper, cut length, corner radius, hole pattern and film — not the sequence.
Decoiling releases the coil's stored bend. Levelling passes the strip through a set of rolls that alternate the bend direction and progressively reduce it, which is what removes coil set and crossbow and produces a flat sheet. The shear cuts to length against a stop. The punch press forms corners and holes in one hit per stroke. Deburring takes the shear burr off the cut edges. Filming applies the PE carrier on the face.
| Step | What it controls | Typical capability | What goes wrong if it is skipped |
|---|---|---|---|
| Decoil | Coil set release | Tension-controlled uncoiler | Strip curls, the shear cuts a banana |
| Level | Flatness, crossbow | ≤ 3 mm/m as the contract figure | Oil-canning after lamination; panel rocks on the post |
| Cut to length | Length, width, squareness | ±0.5 mm shear | Panel will not sit square in a frame |
| Punch corners | Corner radius | R20 / R40 dies | Sharp corners damage film and hands in handling |
| Punch holes | Hole position and diameter | ±0.5 mm, tighter on request | Post holes will not line up on site |
| Deburr | Edge burr | ≤ 0.1 mm; ≤ 0.05 mm on request | Film lifts at the edge; handling cuts |
| Film | Surface protection | PE carrier, one or both faces | Scratches reach the panel before lamination |
Capabilities are the figures we quote against; a drawing that needs tighter must say so, because the step changes from shear to laser or from punch to machining.
Thickness is measured with a micrometer and everyone checks it. Flatness is measured by laying the panel on a surface plate and sliding a feeler gauge under the middle or the corner, and almost nobody checks it until the sign is on a post and the face catches light at a different angle from its neighbour. A panel that is flat when it leaves the leveller can still arrive bowed if it was stacked flat under weight, or if it was cut from a coil with residual stress that only releases when the panel is trimmed.
Two practical consequences. First, put a flatness figure in the purchase order — 3 mm/m is the common contract wording, 1.5 mm/m is available. Second, specify how the bundle is packed: stacked flat and strapped is fine for short sea freight; stood on edge with interleaving is safer for long routes and for thin gauges.
Shear and laser are not interchangeable, and the difference shows up in the documents. Shearing is fast and cheap and holds roughly ±0.5 mm on length and width; laser holds roughly ±0.2 mm and cuts holes and outlines in one program without a die. For a rectangular regulatory blank with four holes, shearing plus a punch is the economical route. For an irregular outline, a large radius, or a hole pattern that has to hold ±0.2 mm against a mating bracket, laser is the honest answer and should be priced as such.
The worst outcome is a drawing that asks for laser tolerances at shear prices: the supplier either declines or delivers to shear and argues later. State the tolerance you need and let the process follow.
One panel off the top of the run is measured for length, width, squareness, corner radius, hole position and burr, then filmed and inspected again. The record goes with the shipment. A first article approved against a drawing is what makes a repeat order a phone call instead of a new project.
Tolerances on thickness, width and flatness for wrought aluminium sheet are defined in EN 485-3, "Aluminium and aluminium alloys — Sheet, strip and plate — Part 3: Tolerances on dimensions and form for hot-rolled products", published by CEN; the corresponding US specification is ASTM B209 from ASTM International. Where a purchase order is silent, those are the defaults that get applied.
Sources: CEN, Brussels · ASTM International, West Conshohocken, PA. Cited 30 October 2026.
The steps are the same for every rectangular blank; what moves the price is whether holes and corners come from a die or a laser, and whether the panel needs deburring to 0.05 mm rather than 0.1 mm. Those are process changes, not volume effects.
Yes, and for small quantities or odd sizes it is often cheaper, because no coil width has to be committed. Coil wins when the size repeats and the width can be matched to the layout.
It is a local wave in the sheet, visible as a distorted reflection. Within the flatness figure in the purchase order it is normal; beyond it, it is a levelling or handling defect and should be rejected at goods-in.
The PE carrier is applied as a low-tack protective film, not laminated with adhesive in the structural sense. The reflective sheeting that carries the retroreflective function is applied later, by the sign fabricator, onto the peeled surface.
Specification questions are answered by the same person who quotes the job.