The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 17 – Mold Frames and Permanent Frames 191
Figure 17-3 Transferring deck camber for a bulkhead from
lofting to plywood stock using a batten and holders.
nails. When the frame material is in the best position,
let the batten back down and trace the station shape by
running a pencil along the inside of the batten. Make
sure the pencil is sharp so that you can mark the line
right up to the batten.
Controlling Edges
After you have drawn the lines on the frame stock, but
before you begin cutting, label the piece with its station
number. Use a felt tip pen and make sure that you
mark on the side on which you’ve drawn the lines.
This is the control side of your frame. <strong>The</strong> edge of this
surface is the controlling edge of your frame.
<strong>The</strong> reason for establishing a controlling edge is
straightforward. It is difficult to keep a hand-held saw
blade perpendicular to the material it is cutting at all
times. When the blade cants, the top and bottom
surfaces of the piece have different outlines. It’s therefore
best, when sawing, to concentrate on following a
line on one surface. This way, you can cut one side of
the material true to form and there’s no confusion about
which lines to rely on. Marking helps to keep track of
which side is the control side.
When it’s time to set up the frames, control sides are
aligned with station lines drawn on a floor or with
notch marks on a strongback. To facilitate beveling, the
thickness of the mold frame material and the width of
the anchoring blocks below go on the side of the line
towards the bow or stern, whichever is nearer. At the
center station, the mold frame material goes on whichever
side you have chosen to put the anchoring blocks.
This changeover point usually occurs at the widest part
of the boat. With this arrangement, anchoring blocks
and mold frame material end up on one side of the
station line, with the legs that connect them on the
other side. <strong>The</strong> controlling edge of the mold frame is
then in a vertical plane above the station line.
We must mention that some builders do just the
opposite of the above by placing the anchoring blocks
and mold frame material on the inside of the station
line and the legs on the outside. In this way the mold
frame edges do not have to be beveled to let the
planking down to the controlling edge. We believe,
however, that beveling mold frames is better, especially
if the planking is stiff and, in bending, will put a lot of
pressure on the frame. If a thin edge is all that there is
to resist the pressure, a certain amount of local crushing
is bound to occur, and the crushing in effect will result
in a distortion of the true edge. Unfortunately, the
crushing is unlikely to be uniform throughout the setup,
and so the planking may not be as fair as it could
have been if the mold were beveled, which gives the
planking support over the width of the frame material.
Mold Frame Halves
Cut out the mold frames with a hand-held saber saw, a
band saw or any handsaw that can follow a curved line.
After you have cut out all the first halves of the frames,
take them back to the lofting floor and place them on
their respective stations to check for any discrepancies.
Make sure that you have a frame for each station and
that each is properly numbered. You will inevitably
need to hand trim edges. Block planes, sharp files, and
coarse sandpaper on a block all work well for this. Use
the controlling edges of these frame halves as patterns
to mark the material for cutting the other halves.
Earlier we stated it was imperative that only half of each
station mold frame be cut out by transferring the line
from the lofting floor. <strong>The</strong> reason for this is that the
control sides of the second halves have to be mirror
images of the original sides. Except in the case of the
tracing paper method, in which paper can just be
turned over, it is not possible to get both a straight