The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

110 Core Boatbuilding Techniques
the surface, but pressed well together so that there is
neither over nor under matching of the bevels (See
Figure 12-3.) Determine straightness in the edge
dimension by feeling the edges of the scarf with your
gloved fingers or set up a straightedge on the flat
surface against which you can assemble the two pieces
of stock, thus ensuring straightness in both dimensions.
When you have lined up the scarf joint perfectly, locate
a staple along the edge of the scarf joint on one surface,
turn the stock over, realign the joint, and locate another
staple on the opposite surface in the opposite scarf
edge. <strong>The</strong>se temporary locating staples hold the scarf
joint in proper position until you can apply clamping
pressure.
It is important that you clamp the joint firmly so that
good contact is made between the surfaces. However,
excessive clamping pressure is not needed and should
be avoided because it may pre-stress the joint unnecessarily.
To facilitate cleanup, remove any excess epoxy
that has squeezed out of the joint before you apply any
clamping pressure. <strong>The</strong>n wrap the scarf joint in wax
paper or light polyethylene film to prevent inadvertent
bonding of the scarf joint with clamps or the flat
surface. Apply clamping pressure with any number of
clamps desired or make up simple clamping fixtures
utilizing wedges to apply even pressure over the entire
scarf joint. Often we insert a clamping pad between
the clamp and the stock being clamped to distribute
Figure 12-3 When bonding thin stock or more than one
scarf, take care to avoid overmatching the bevels (A) or
undermatching the bevels (B). Use wire brads or staples
to hold a bevel in proper alignment (C) and prevent slipping
during clamping.
clamping pressure over more area and prevent clamp
marks from appearing in the face of the stock.
When manufacturing the planking, stringers, or
ribbands for a mold or hull, you will bond a great
many scarf joints in a short time. Just as we have
developed higher production methods to machine
scarf bevels, so have we developed techniques which
vastly speed up the scarf bonding procedure. When
making numerous scarfs with the same size stock, we
prepare and temporarily line up the joints and then,
rather than clamping them individually, apply adhesive
and clamps to a number of scarfs in one operation as
shown in Figure 12-4. <strong>The</strong> number of joints that you
can assemble at one time is limited by the assembly life
of your epoxy and the dimensional capacity of the
clamps or clamping fixtures you are using. While we
have clamped up to twenty scarf joints at once, it takes
a great deal of care to keep this many from shifting.
Figure 12-4 Stringers being prepared for bonding and
clamping. Scarf bevels have been cut on both ends. This
set-up places scarfs close to each other to minimize the
number of clamps needed.