turn the screw back to the mark. For most joining procedures, any disrup-
tion of the panel’s position relative to the screw clamps necessitates minor
readjustment when the joint is finally brought together.
Depending on the joint, the glue can be applied with the entire
panel removed from the apparatus, or, if the joint consists of two pieces,
one piece can be positioned and clamped in place while the other piece is
moved slightly away to create a sufficient gap. The open structure of the
apparatus allows considerable access for brushes and fingers.
Next, the glue is applied. Care and ingenuity must be used for
partial disjoins, especially splits with both ends closed. An excess of glue
is worked into the break, preferably from the panel back. Methods to
increase glue penetration include finger pressure, slight flexing of the joint
edges, suction, positive air pressure, and use of a syringe or a spatula. For
better wetting of the joint faces, a more dilute glue may be applied first,
then a more concentrated glue. The highest practical concentration should
be used to avoid “starving” the joint,^12 a condition that can occur with
glues that shrink or dry by moisture or solvent loss or with glues that are
partially absorbed by porous woods.
To produce as complete a joint as possible, it is sometimes better
to leave a sufficient line of excess glue on the back of the panel only,
since glues that dissolve or disperse in water or solvent usually shrink
into the joint. Any outstanding dried glue is then removed to the level of
the panel surface.
The clamps are reset, and joining pressure is applied lightly in
small increments, with alignment readjusted if the joint slips. The aim is
to maintain alignment while forcing excess glue out of the joint in equal
measure from the front and back of the panel. This indicates that the join-
ing faces are meeting squarely.
If joining pressure is directed nearer to the front or back of the
panel, a gap may result toward the opposite side. This occurs, for example,
when a buckling deflection is induced in a panel with an inherent warp
(Fig. 5). The chances ofmaking a starved joint can be reduced by a slight
increase in overall pressure in two or three stages during the initial drying
period. In this way, shrinkage and absorption of the glue are countered by
a reduction of the joint gap.
It may be necessary to readjust the alignment screws intermit-
tently between successive increases of joining pressure. This is especially
true for thin, flexible panels and for disjoins, where movements are more
likely. Disjoins, because they are usually straight and smooth, are often
prone to slippage as joining pressure is applied (Fig. 8). Joint slippage
can occur imperceptibly, long after the final pressure settings have been
made and well into the initial setting stages of the glue. It is necessary
tocheck the alignment repeatedly in all directions until the glue is set to
ensure best results.
After the glue has dried, pressure mechanisms are released in the
order opposite to which they were applied during the gluing procedure
(first the bar clamps, then the alignment screws). The bar clamps are
backed offin small increments, in the order and to the degr ee in which
they were applied. Any unexpected movements or sounds may signal a
critical weakness. If the alignment screws are released before the bar
clamps, then critical support may be removed prematurely from the joint
area, and the panel may buckle.426 Brewer
Figure 8
Slippage movement (indicated by vertical
arrows) induced under joining pressure (indi-
cated by horizontal arrows). This type of slip-
page occurs when the axis of the joint is not
parallel to the panel edge(s) and therefore is
not perpendicular to the applied pressure.