COOLDELO

Kerf, Fit & Finger Joint Calculator

Turn your measured kerf into slots, holes and finger joints that actually assemble.

Free No signup Runs in your browser Stop guessing joint tolerances

Measured values

Desired fit

Everything is calculated in your browser. Nothing is uploaded.

What is kerf?

Kerf is the material the beam removes. A 0.15 mm kerf means every hole comes out 0.15 mm larger and every part 0.15 mm smaller than drawn. Ignoring it is the most common reason finger joints are too loose or too tight.

Fits and clearances

  • Press fit — 0 to 0.05 mm clearance. Needs mallet assembly, best for permanent joints.
  • Snug fit — about 0.1 mm. Holds by friction, can be disassembled.
  • Slip fit — about 0.2 mm or more. Easy assembly, needs glue.

The calculator returns the nominal slot width to draw in your CAD file, the compensation value to apply to the drawing, and a sensible tab count for the edge length you are joining.

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