VENEER GRADING Rules PART 2 Different wood veneer cut types
Rotary cutting is a method used to peel a log into thin sheets of wood as if unrolled from a spool, like paper towels. Rotary cut veneer has a variegated grain appearance, and can vary tremendously, although it is the preferred method to obtain large sections of wood to manufacture whole piece faces in standard and oversize structural marine grade panels. It is usually the least expensive veneer style. Rotary cutting is the only way to achieve a 48″ wide whole-piece face.
Quarter slicing (also known as Quarter Sawn, Quarter Cut or Quartered) is a cutting method that involves dividing the log into quarters and slicing the quarter log on a radial direction approximatelyperpendicular to the growth rings to produce a straight grain appearance with the flake from the wood rays typically exaggerated on the surface. It is commonly used with red and white oaks because of the desired flake effect, but may be used on any species. Avoiding the flake effect and obtaining tighter grain
appearance calls for a rift cut.
Rift cut veneer is commonly produced in the various species of Oak. Oak has medullary ray cells which radiate from the center of the log like the curved spokes of a wheel. The rift or comb grain effect is obtained by cutting at an angle of about 15% off of the quartered position to avoid the flake figure of the medullary rays
Plain slicing (also known as Plain Sawn or Flat Cut) a log produces thin veneers that are no wider than the log and have a pronounced repeating grain pattern. These pieces must be combined to make a plywood face by “matching” the pieces as desired by the customer.
Matching is a term typically used in reference to the relationship between one veneer strip or “component” and the adjacent component in a face consisting of more than one component. The individual components are spliced together employing one of a number of matching techniques. The most common is book matching, which requires reversing every other component as if you were opening the pages of a book. The result is a mirror image at the splice line.
Slip matching involves splicing each veneer to the next without turning over any component.
This allows the face to have the tight side of the veneer out on each component, which helps avoid the “barber pole” effect of book matching.
The term “matching” may also be used in reference to the relationship of all components within a panel face. Running matching means the outer components will not be the same width as the inner components due to jointing the log so as to produce the greatest yield. Running match will be provided unless otherwise specified. Balance matching requires all components to be the same width and Center matching requires that there be an even number of same width components. Because of final panel trimming, the outer components of both balance and center matched faces will be slightly narrower than the other components. Center Balanced is typically specified for doors, allowing best positioning/yield.
The term “matching” may also apply to the relationship of one panel to the next. Sequence matching means the panels are produced from faces that were kept in order and numbered during the manufacturing process.
Tight Side and Loose Side
Conventional means of peeling or slicing a log results in the development of minute fractures known as lathe checks on the side of the veneer adjacent to the knife and closer to the center of the log as the veneer was cut. The side of the veneer having the lathe checks is the loose side, while the opposite side is the tight side. The loose side will tend to absorb more finishing material than the tight side, which sometimes results in a dark/light appearance called the “barber pole” effect.
The “Barber Pole” effect
“Barber pole” refers to the alternating dark and light appearance that is occasionally observed in book matched veneer as a result of the different surface characteristics that exist between the tight side and loose side of a given veneer, especially noticeable after finishing. Barber pole effect can be avoided by using matching techniques that utilize tight-side-out assembly.
A calibrated panel is typically a veneer core panel whose core was produced in a separate step and sanded to strict thickness tolerances before the outer decorative veneers are applied. Natural variation such as density, moisture absorption, and physical properties, combined with manufacturing variation results in thickness fluctuations in all wood panels. Veneer core typically has more potential thickness variation than engineered cores. A calibrated panel is designed to provide even tighter tolerance restrictions.
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