How to use box joint finger layout
What this calculation does
A box-joint layout divides a board into an odd number of equal alternating finger-and-slot sections.
Measure board width and choose an odd section count of at least three before marking from one edge.
Enter the measurements
- Board width: Measure width across the joint.
- Odd number of equal finger/slot sections: Choose an odd count of equal sections.
Formula and variables
Section width = board width ÷ odd section count. Mark each interior boundary at section width × integer positions 1 through section count − 1.
Section width is board width divided by section count. Interior boundaries lie at integer multiples of that width.
Read the result
A 4.5 in board split into nine sections has 0.5 in sections and marks every half inch through 4 in.
Worked example
Inputs: 4.5 in board divided into nine equal alternating sections
- Section width = 4.5÷9 = 0.5 in.
- Interior marks are 0.5×1 through 0.5×8 = 0.5, 1, 1.5, 2, 2.5, 3, 3.5 and 4 in.
Expected result: 0.5 in sections and marks at 0.5 through 4 in
Frequently asked questions
Does the layout compensate for saw kerf?
No. Jig offset, kerf and test-fit adjustment are separate.
Why must the count be odd?
This model uses an odd alternating section count for the declared centered pattern.
Conditions, presets and technical notes
Assumes a centered alternating finger/slot pattern on a board with an odd number of equal sections. Does not include kerf compensation, jig offset, test-fit adjustment or a separately calculated mating board.