SOLID WOOD MACHINING
The preparation of joints as well
as the adhesive itself plays a critical role in the quality of fingerjointed products. Most failures of
fingerjointed lumber are caused
by poorly machined and poorly
fitted dry joints. The adhesive
is a factor in heat and water-resistance, however, even the best
adhesive available cannot make
up for a poor-fitting joint.
Here’s some common prob-
lems, causes and solutions for
1Pressed fingerjoint blanks fall apart. Probable causes: ( 1) Glue penetra-
tion into wood is not adequate.
( 2) Temperature is too cold to
allow glue to form a reliable bond
and chalking occurs. Solutions:
( 1) Moisture content of wood is
too high (above 15%). ( 2) Keep
boards and surrounding work
area above minimum use temperatures.
2Joint fingers are too short or too long. Probable causes: Fingers are too
long: The fingers must be short-
ened by increasing the amount
of wood the trim saw removes.
Fingers are too short: They must
be lengthened by reducing the
amount of wood the trim saw removes. Solutions: A good fingerjoint will have no gaps, allowing
very little room for excess glue.
This is accomplished when the
fingers are equal in lamination.
3Joint fingers have concave gap on side. Probable cause: The cutters were
not resharpened according to the
hook gauge or the cutters have
too sharp of a hook angle. Solu-
tion: Grind the cutters to match
the hook gauge.
4Joint fingers have a convex gap on the side. Probable causes: ( 1) The
cutter stack moved during setup
and rotated too far forward for
the correct set-up angle. ( 2) The
cutters were not resharpened
according to the hook gauge or
have too blunt of an angle. ( 3)
The cutter stack was not pulled up
to the alignment post. Solutions:
( 1) Reset the head and check the
alignment of the cutter stack. ( 2)
Grind the cutters to match the
hook gauge. ( 3) Set the cutter
stacks against the alignment post
of the set-up stand.
Source: Franklin Adhesives & Polymers.
For more information call 800-877-4583 or visit
Pointing a finger at four joint problems