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.

Finger Jointed Lumber

I have been thinking and obsessing about finger jointed lumber off and on for the past 5 years. It all started when I visited a Georgia Pacific- Finger Jointing Mill in Tylertown, Mississippi. In T-town, they get all the cut-offs (cut off pieces from saw mills, usually 6-18 inches long) and finger joint them into 2x4 or 2x6 studs. These studs are straight as a die (no warping), defect free (no knots) and they are precision cut to length.
Finger jointed lumber is an engineered wood product. It's nothing new, people have been splicing lumber and gluing it up for a century. Today finger jointing can be found anywhere wood is being used.
What I like the most about finger jointed lumber is it's simplicity and efficiency. You can take small pieces of lumber that would have no real practical purpose by themselves, but when profiled and glued to one another, blam!

A true synergy of resource utilization and efficiency.