Guide 02 / 06 · 5 min read

V-groove for 4 mm ACM: cutter angle, depth, residual skin and layers

ACM 3D Studio · Published 21 September 2026

01What a V-groove in aluminium composite is

Aluminium composite (ACM, Alucobond, Dibond) folds without a press brake: a V is milled from the back, removing the rear skin and almost all the core, and the panel is folded by hand around the thin front skin left in place. A groove of apex angle θ closes by rotating the material by θ from flat. The finished corner (dihedral) is 180° − θ.

So two angles meet in the workshop. The nominal angle is the one printed on the cutter in the catalogue; the apex angle is the tool’s own, the only one the engine handles. Under the dihedral convention (machine profile default), a “135° cutter” makes a 135° corner and has a 45° apex angle. Under the apex convention, the number is the tool angle. The machine profile fixes the convention once; the DXF names its layers by the nominal angle, which is what the operator reads to mount the tool.

02Width and depth: the formula

depth = e − s
width = 2 · (e − s) · tan(θ / 2)

e = thickness, s = residual skin, θ = cutter apex angle

With the ACM 4 mm material profile defaults — thickness 4 mm, residual skin 0.4 mm — the depth is 3.6 mm for any cutter, and the width depends on the angle:

For 3 mm ACM, the same skin gives a 2.6 mm depth and a 5.20 mm width at 90°; for 6 mm, 5.6 mm depth and 11.20 mm width. The residual skin is a material profile setting: a zero skin or one above the thickness is refused by the engine (SKIN_INVALID), the groove would go through the panel.

03Why the residual skin is 0.4 mm

The front skin of a façade-grade aluminium composite is about 0.5 mm; leaving 0.4 mm at the bottom of the groove keeps the front aluminium intact with a fraction of the core. Too little and the fold cracks or marks the face; too much and the fold resists and the corner rounds off. The value is a profile default, offered at creation: the workshop owns it and corrects it with use, with the same coupon as for the deduction.

04What the generator does with an angle that has no cutter

The workshop owns a finite set of cutters. A fold is matched to a cutter within ±0.5°. When a family asks for a missing angle, the engine does not stop at an error:

• CUTTER_UNAVAILABLE names the required angle and the nearest cutter, with the signed gap.
• DOUBLE_GROOVE_AVAILABLE proposes two consecutive folds at standard angles (θA + θB ≈ required) separated by a band whose width is max(2·e, 6) = 8 mm on 4 mm, never less than the half-widths of both grooves plus one thickness, otherwise they would cross.
• REQUIRES_BEND: the required angle is below the smallest cutter; a double groove can only add rotation. The fold goes to the press brake.
• On the facet folds of a relief (open V), the smallest cutter whose apex angle exceeds the requirement is taken and the V stays open: GROOVE_LEFT_OPEN, an information.

The family, which alone knows its parameters, additionally proposes the setting that lands on an available cutter: “set the wave amplitude to this value for a 135° fold”.

05Front-side grooves: concave folds

A concave fold (material turning towards the front) is grooved from the visible face. In the model the angle is negative; in the DXF the axis goes on a RAINURE_AVANT_<n> layer (colour 30), expressed in the same frame as the rest, back view. The operator flips the sheet for the second pass and a thin line stays visible on the front. Decorative panels alternate back and front grooves this way; the V cassette has its central fold turned inwards.

06What the operator checks before starting

1. The machine profile angle convention matches the marking on the cutters.
2. Residual skin and thickness of the material profile match the loaded sheet.
3. Every RAINURE_<n> layer has its cutter mounted; RAINURE_AVANT_<n> layers are done with the sheet flipped.
4. On a flat cassette, the return exceeds the groove width plus half the deduction (7.2 + 2.0 = 9.2 mm with the default deduction), otherwise the groove eats into the return (GROOVE_TOO_DEEP).

Open the flat cassette in the studio to see these values on the cut sheet, or read how the DXF is organised.

Read next: calibrating the bend deduction with a three-fold coupon.