Quickie Q2 Lite Construction Manual - page 44
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The hot wire should be guided around the templates with light
pressures. Pushing too hard against the template may move them or flex
the foam block which results in an under cut foam core.
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The correct set-up is just as important as using the correct
tools and materials. Foam is a fairly flexible material and an
improper set-up can cause deflection. The foam block should be well
supported at each end, so that it doesn't sag and doesn't move around
while being cut.
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You need clearance for the hot wire cutter to pass by the table
and the weights used to hold the foam steady.
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Foam is manufactured in sizes that are often too small to get a
complete core from a single block. it is necessary to use two foam
blocks to get the size required for the wing cores. These blocks have
to be joined using an epoxy/microsphere mixture. The hot wire won't
cut through the micro joint, so all of the hot wire cutting is done
with the blocks temporarily joined. Nails or blobs of 5-min epoxy are
used for temporary foam joints, but the hot wire won't cut through
these. Thus, they have to be placed carefully so that the wire doesn't
have to pass through them.
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Don't be overly concerned if you don't make perfect foam cuts:
ridges on the foam core from inadvertently lifting the hot wire off
the templates are easily faired in with a sanding block. A less-than-
perfect leading edge can be blended in by sanding after the foam core
is assembled. Gouges in the foam can be smoothed and filled with dry
micro to contour after applying the glass skins. The foam is too
expensive to throwaway because of a minor gouge.
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A finished foam core may warp out of shape after it is removed
from the original rectangular block. This is due to internal stresses
in the foam from the manufacturing process, and is no cause for
concern.
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A warped core is simply weighted into the jig blocks and shimmed
straight prior to glassing. Once the skin has been installed, the foam
is held firmly in position by the sandwich structure.
URETHANE FOAM SHAPING
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One of the real treats in the construction will be shaping and
contouring urethane foam. Urethane is a delightful material that