Give 'em the finger

Here is a little background on the venerable finger joint. The finger joint is made up of little "fingers" that are profiled into the edges of the wood. Finger jointed lumber used for structural purposes is usually dimensional lumber, 2x4's and 2x6's that are finger jointed at the ends, glued up, joined together and pressed until the adhesive cures.


Based on research, the strength of the finger joint is based on four parameters:

1. length of fingers
2. slope of fingers
3. tip thickness
4. pitch

A 1.18 inch finger with a 1:12 slope (parallel to the grain) and a .5-.7 millimeter tip produces the strongest finger joint. There have been studies showing that the tensile strength of finger joints can be 80-100% of solid sawn lumber.