Veneer quality control Part 2 Tightness and looseness

Veneer quality control Part 2 Tightness and looseness

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Veneer is characterised by the presence of small checks or fissures roughly parallel
to the grain commonly referred to as lathe or peeler checks. These checks form
on the underside of the veneer that is in direct contact with the knife as the
veneer passes between the knife and the nose bar as it is being cut from the billet
and flattened out (Figure 7.9). The underside of the veneer containing the lathe
checks is referred to as the loose side and the upper side is referred to as the tight
side. Veneer that has many deep lathe checks is termed ‘loose-cut’ veneer while
veneer having shallow infrequent checks is termed ‘tight-cut’. Lathe checks will
affect the veneer quality significantly; and a balance is required between tightness
and looseness.
Veneer with optimal tightness has only small and fine peeler checks, and has
little tendency to curl, buckle or split during drying. Fewer peeler checks mean
greater strength across the grain and tight-cut veneers are less likely to rip or split
during manual handling. Tight veneers are associated with superior weathering
properties and exhibit less finishing faults. However, veneer that is too tight can
cause pressing problems if the veneer has not dried flat. Deep peeler checks and
rough surfaces significantly increase the surface area of the veneer (up to three
times), leading to excessive absorption of adhesive and/or surface coatings and
distorted reflection of light (relevant for appearance grade)

Surface roughness
Surface roughness results from factors such as excessive peeler checks, splits and
grain tear-out. Roughness originates from splitting ahead of the knife edge during
the peeling process due to cleavage action of the knife. The direction of splitting
in relation to the cutting path determines the degree of severity of roughness. The
development of roughness in the peeler billet is also dependent on and intensified
by inherent lines of weakness within the timber (fibre direction, wood rays and/
or growth ring slope), pith eccentricity and cross-grain.
The two main disadvantages of surface roughness are the reduction in veneer
grade class and manufacturing complications (e.g. increased adhesive usage
because of the increased surface area and reduced bond quality.
Optimal lathe settings, combined with appropriate pre-treatment of the billet, are
effective methods to minimise surface roughness.

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