Depth is the variable that fails
Industry guidance is consistent: leave 0.2–0.5 mm at the bottom of the groove, roughly 60–70% of the thickness removed. Too deep and you sever the skin — the panel cracks at the line. Too shallow and the panel will not fold flat; it fights you, and the stress cracks the skin anyway.
Bits and angles
A 90° V bit with a flat tip around 3 mm for right-angle returns; a 135° bit where the design wants an obtuse fold. On fire-rated or mineral cores, carbide dulls fast and the depth drifts mid-sheet — that is a PCD job.
Order of operations
Cut the outline and notch the corners through. Rout the grooves. Fold away from the face, in the order that keeps the panel flat on the bench. Bond or mechanically lock the corners — the groove is a hinge, not a structural joint.
What we generate
The DXF carries OUTLINE (through cut) and VGROOVE (partial depth) on separate layers so the router or the CAM software routes them as two operations. Millimetres, 1:1, R2010, units set in the header — the thing that most often makes a DXF cut 25.4× too big.
Questions
Should the groove be on the front or the back?
The back. The untouched front skin is the hinge and the visible face; grooving the face severs the finish.
Can you fold ACM without a V-groove?
Not to a crisp 90 degree return. ACM has a plastic core and thin skins; a plain brake bend kinks and crazes the coating.
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