The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

112 Core Boatbuilding Techniques
Scarfing Plywood Panels
<strong>The</strong>re are major differences between scarfing lumber
and scarfing commercially manufactured plywood
panels. One significant dissimilarity is dimension: a 6"
or 8" (150mm or 200mm) wide scarf joint in lumber is
considered large, but a 4' (1200mm) or even 8'
(2400mm) wide scarf joint in plywood is standard.
Plywood is usually much thinner than lumber and
therefore plywood bevels are usually shorter. Unlike
bevels in stock, which consist entirely of end-grain
wood, plywood bevels have both end and flat grain.
Because plywood differs from lumber as a material, the
methods used to cut plywood bevels and bond
plywood scarf joints are somewhat different from
those used with lumber.
Plywood is such a commonly used material in modern
wooden boatbuilding that the ability to join plywood
panels with a sufficiently strong joint is of major importance.
<strong>The</strong> average boatbuilding project also uses
enough plywood so that plywood scarfing requires a
significant number of labor-hours in relation to the
boatbuilding project as a whole. We recognized this
problem long ago in our own shop and developed a
guide which could be assembled on a table saw to
direct a plywood panel across the table saw blade and
create a perfectly sawn bevel edge in a short period
of time. <strong>The</strong> only difficulty with this fixture was that
we had to use the table saw for many other things
and, therefore, had to set up and remove the fixture
frequently. <strong>The</strong> set-up procedure required at least 20
minutes, so unless we had a lot of bevels to cut on
plywood, we usually planed them by hand.
To solve this problem, we adapted our table saw device
and attached the guide to the bottom of a hand-held
circular saw. What we liked best about this tool was
that we could leave it in place on the saw, ready for use
at any time with no set-up required. <strong>The</strong> combined cost
of a saw and attachment was so low that we could well
afford the luxury of keeping the device permanently
attached to an extra saw. Eventually, because we found
it so useful, we added it to our line of WEST SYSTEM
products. We also show another alternative, building
a production jig for cutting plywood scarfs.
<strong>The</strong> Scarffer attachment
<strong>The</strong> Scarffer circular saw attachment, shown in Figures
12-6 through 12-8, is inexpensive and can be bolted to
Figure 12-6 Setting up a straightedge for the Scarffer
attachment.
Figure 12-7 Cutting a scarf bevel by running the saw with
the Scarffer attached along the straightedge.
the bottoms of most 7 1 �4" hand-held circular saws. It
comes with step-by-step instructions for attaching it to
a saw, setting up plywood panels, and sawing bevels.
<strong>The</strong> Scarffer attachment is ideal for work with plywood
up to 1 �4" (6mm) thick, and with minor hand finishing
may be used on panels up to 1 �2" (12mm) thick. We feel
that it is an investment that quickly pays for itself in
labor savings, even on small projects. Bevels cut with
the Scarffer attachment can be more accurate than handcut
joints, especially when you have little experience
making scarfs by hand.