Kerf calibration tester

How to use

1. Cut the file on the same material you'll use for boxes — both pattern and material thickness matter.
2. Caliper square (left): measure the outer edge with calipers. kerf = 30 − measured_mm. The inner 10 mm hole gives the same kerf via kerf = measured_hole_mm − 10.
3. Fit ladder (right): try each tab in the slot. The one that's press-fit (snug but not forced) gives you your kerf — read it off the label printed below each tab.
4. Type that kerf value into the box maker's Kerf field for press-fit finger joints.