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Hingesmith
Studio
Open Studio

Living hinge calculator

Enter your plywood thickness, hinge pattern and bend radius and get the widest safe cut spacing, the link width it leaves, and the tightest bend the pattern can make. The same model Hingesmith uses to space every cut.

Column spacing
2.20mm
Centre to centre. Leaves 2.05 mm of wood between cuts; 46 columns per 100 mm of curve.
Cuts per column
2
36 mm dashes on an 80 mm wall, alternate columns running out through the edges.
Tightest bend, this pattern
R4.6mm
At the densest spacing the pattern allows.
Corner radius the Studio uses
R8mm
Every catalog corner on 3 mm stock is at least this, so no shape asks for more than the hinge gives.

Model: each link between two columns twists by spacing ÷ radius; plywood takes about 1.2% shear strain (the boxes.py FlexBox default). The Studio measures each pattern on a test strip and spaces every point of a wall from the curvature there; the free bend test tells you whether your sheet is stronger or weaker than that.

Build a box with this hinge About the Straight Lattice

Questions

Which radius do I enter?

The radius of the neutral axis: the inside radius of the curve plus half the stock thickness. A 20 mm inside radius on 3 mm plywood is 21.5 mm.

Why does the spacing change with the pattern?

Each pattern leaves links of a different length and shape between its cuts, and a link’s twist per unit of curvature depends on that. The calculator measures each pattern on a test strip, as the Studio does, rather than using one rule for all of them.

My plywood seems stronger (or weaker) than this.

Plywood varies by supplier and sheet. The free bend test strip in the Studio loads the links to 70, 100, 140 and 200% of the limit used here; the highest zone that bends cleanly tells you how far to move the limit for your sheet.

Does this work for acrylic or MDF?

No for acrylic, which has no fibres to twist and shatters. MDF manages gentle curves at about 70% of the limit; the calculator’s numbers assume plywood.