Series editors' preface - Wood Tools

microballoons. They may be levelled before
the adhesive has completely cured using
wetted tools, or simply carved after the epoxy
has set.
Interventive restoration methods used in the
past to reinforce butt joints or ensure a level
surface have included loose tongues and dovetail
keys. If the grain of the loose tongue runs
parallel to the main components it offers no
additional strength, unless the edges of the butt
joint were in very poor contact. If plywood
tongues, cross-grained tongues or dovetail keys
are used there is the potential for further
damage as a result of differential movement.
Large dovetail keys may prove particularly
problematic and may lead to the creation of
new splits where wood movement is restrained
(see Chapter 7).
When wooden elements within a joint are
broken or have severely deteriorated it may be
necessary to cut new parts, add new wood, or
reinforce broken parts with veneer, splines,
loose tongues or dowels. A common problem
occurs as a result of woodworm attack that has
concentrated on mortise and tenon joints.
Severe damage necessitates the replacement of
the original tenon with a false tenon that
extends into the rail to provide adequate
surface area for a strong adhesive bond (see
Figure 10.2). The false tenon must be a tight
fit to the mortise and the rail. Gaps that result
from compression set in a mortise and tenon
joint may be built up with veneer. In more
severe cases, for example insect attack, it may
be necessary to fit a patch and recut the
mortise in fresh, undamaged wood.
Knuckle joints are used to attach fly rails or
legs to the main carcase frame of drop-leaf
tables. Fly rails or legs support the leaf when
it is raised for use. Good cabinetmaking skills
are required to produce a well-made knuckle
joint and the critical process is drilling the pivot
hole so that it is absolutely vertical and exactly
centred in both sets of knuckles. Knuckle joints
are prone to wear on the horizontal faces,
which results in racking of the fly rail or leg
and may lead to damage or breakage of the
pivot pin. If the joint is in regular use it may
be necessary to add veneer or thin fillets of
wood to compensate for wear on the knuckles.
The pivot pin was often made from steel
or iron, approximately 3 ⁄16 inch (4.5 mm) in
diameter. If the pin is broken or has partially
Principles of conserving and repairing wooden furniture 461
Figure 10.12 Cramping a knuckle joint to redrill the
pivot hole
seized it may be tapped out and a replacement
fitted. It may be necessary to drill a larger hole,
in which case the joint must be cramped up as
illustrated in Figure 10.12. If wood is used for
a replacement pivot pin it should be slightly
softer than that in the knuckle joint itself so
that wear is absorbed by this replaceable part
rather than the knuckles. Screws are liable to
snap as a result of shear and should not be
used as pivot pins.
Many problems with rule joints are caused
by faulty fitting of hinges (see section 10.3.3).
Other problems may be caused by warping of
a drop leaf or swelling that may result in the
joint binding. The narrow lip of the cove
moulding on the drop leaf is vulnerable to
damage if the hinges are loose. Excess leverage
applied when the leaf is lifted may also
cause splits or breakage.
10.3.2 Shrinkage checks and splits
Surface checks are unusual in solid wood
furniture in a well-maintained environment
(Figure 10.13). Surface checks are often
encountered in furniture that incorporates
rotary cut veneer, for example the moulded
plywood furniture associated with twentieth
century designers such as Marcel Breuer or
Charles Eames. Minor (1993) found that lathe
checks, caused in the manufacture of rotary cut
veneer, were exacerbated by fluctuations in
relative humidity. Filling surface cracks in
plywood will exacerbate the problem. Lathe
checks and surface cracks in rotary cut
plywood veneer are an inherent part of the
ageing process of this material.
Shrinkage splits in furniture and wooden
objects are caused by the dimensional change
of wood in response to a reduction in relative
humidity in combination with a fitting or joint