The free bend test: find out how far your plywood bends before you cut a box
Hingesmith’s bend test kit is a free strip with four hinge zones and a gauge plate. Cut it once per sheet of wood, read the result and set Wood flex so every box is cut for that plywood.
5 min read
No two sheets of plywood bend the same. The bend test is a small free cut that tells you how far yours will go, so you can tune every box to it instead of hoping.
What is in the kit
The download is one SVG with two parts:
- The strip. Four hinge zones, side by side, each labelled with a load: 70%, 100%, 140% and 200%. They all use the same cut spacing, the one the Studio would pick for a gentle curve on your stock, and the same hinge pattern you have selected.
- The gauge plate. A plate with four rounded corners, one per zone. The 70% corner is the largest radius; the 200% corner is the tightest. Wrapping a zone round its corner twists the links to exactly that share of the standard limit.
The strip is laid out exactly like a box wall: alternate columns run out through the edges, the solid bands at the ends are compensated, and the labels sit clear of the cuts. What bends on the strip bends on the box.
Running it
- In the Studio, pick the hinge pattern and the stock thickness you plan to cut the box from. Go to the Hinge tab and press Download bend test.
- Cut it with the settings you will use for the box. Score first, then cut.
- Hold the 70% zone against its gauge corner and wrap it round, slowly, with your thumbs close to the bend.
- Repeat for 100%, 140% and 200%, listening for cracks and watching the outside veneer for tears.
Reading the result
| Highest clean zone | What it means | Wood flex setting |
|---|---|---|
| 70% only | Weak sheet: brittle veneer, voids, or charred links | 70%: cuts move closer to protect it |
| 100% | Good Baltic birch; what the catalog is tuned for | 100% (the default) |
| 140% | Better than standard | 140%: fewer cuts, tighter bends allowed |
| 200% | Unusually supple sheet | 200%: the fewest cuts |
Set Wood flex in the Geometry tab, under Material. The hinge is re-spaced from that limit immediately, and the Twist load readout in the Hinge panel reports every box against it from then on. Fewer cuts mean a faster job and a stiffer wall; more cuts mean a wall that bends more easily.
When to run it again
- A new batch or supplier of plywood, even at the same thickness.
- A different thickness: 4 mm and 6 mm have their own strips.
- After changing cut settings, a lens, or the focus height.
- If you switch pattern families, say from the Straight Lattice to the Serpentine. The strip is pattern-specific.
Pair it with the kerf test on the same sheet and both of the numbers that decide fit are in hand before the first box.
Questions
Is the bend test free?
Yes, for every hinge pattern and stock thickness, with no account. Free plans cut it at the default 0.15 mm kerf, as for any free export.
Why does the strip have four zones?
Each zone is spaced so that wrapping it round its gauge corner loads the links to 70%, 100%, 140% or 200% of the standard twist limit. One strip therefore brackets your plywood from "weaker than standard" to "twice as strong".
Does Wood flex change the test strip?
No. The test always uses the standard limit, because it is what the setting is calibrated against. Only your boxes change.
What if the 70% zone cracks?
That sheet is not hinge material, or the settings are charring the links. Check the cut at low power under a loupe; if the links look brown and crumbly, slow down and reduce power. If they look clean, try a different sheet.
Try it on a real box
The Studio runs in your browser. Three shapes export free, no account needed.
Open the Studio