The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

94 Core Boatbuilding Techniques
Figure 11-5 Cleats are screwed to a baseboard to force
laminates into the shape required. Clamps in the pile in the
upper right will be used during the dry run and the final
lamination.
procedure. Shield the framework from clamp marks
with the use of clamping pads and protect members
against any excess epoxy with a plastic sheet barrier.
Figure 11-4 shows some frames being laminated using
the stringers as a form. Further details on this type of
laminating procedure are discussed in Chapter 21.
Allowance for Springback
All laminations will relax from the curve that they have
been clamped to. This springback may range from 1 ⁄16"
to several inches, depending upon two factors: the
severity of the curve the lamination must take, and the
number of pieces used to make up a lamination. <strong>The</strong>
object, of course, is to try to anticipate what the springback
might be and then to overbend your lamination
so that when it relaxes, it will assume the exact shape
desired. Refer to Figure 11-6 to determine the amount
of springback that a lamination will have. It is rare for
a lamination to end up exactly as desired, although
you can come very close and then take several corrective
measures, which will be discussed later.
<strong>The</strong> Dry Run and Clamping Procedures
If you don’t have much experience or if you are faced
with a complex or unusually shaped form, try a dry run
of your lamination. Assemble and clamp your pieces
with no epoxy to see if there are any flaws in your
approach. Also check at this time to be sure that you
have enough clamps. Because there is no epoxy in the
way, you will be able to see gaps and take appropriate
When a strip of wood, a ply, is bent to a curve and released,
it springs back to its original shape. A stack of loose plies
will do the same. When these plies are glued together while
clamped to a curve, they tend to stay curved, but will
straighten out or spring back a little. When building the
mold or form for the laminate, it’s common to make the curve
a little tighter to compensate for the springback. <strong>The</strong> amount
of springback depends on the number of plies in the laminate,
not in the ply material or the ply thickness. A simple formula
can help predict the amount of springback you can expect:
y = x/n2 y = the amount of springback
x = the amount of deflection
n = the number of plies
Thus with four plies, the springback (y) will be 1 ⁄16" if the
amount of deflection (x) is 1". By using plies half the thickness,
you double the number of plies for a given thickness
of laminate and reduce springback four times—in this case
to 1 ⁄64".
Figure 11-6 Computing springback in a curved laminate.
From Fine Woodworking 119, July 1996.
corrective action, including increasing clamping
pressure and re-machining your stock. Once WEST
SYSTEM epoxy is applied, you will have only a short
time to correct any mistakes. If something goes wrong,
you could lose the whole lamination and all the work
and material that goes with it.
To distribute clamping pressure over more area, make
up clamping pads out of pieces of wood to be placed
between the clamp jaws and the stock. <strong>The</strong> pads will
also prevent any clamp marks from occurring on the
lamination surface. When you have clamped the lamination
to your satisfaction, it is sometimes helpful to mark
the position of each clamp on the stock so that you can
reposition it quickly when actual laminating begins.
When you remove the clamps from their trial run
positions, place them close by so that you won’t have