The grain structures of different species of wood vary tremendously and as a naturally grown product they vary within their own species from tree to tree. By applying different techniques to the process of slicing the logs into veneers the grain characteristics of the wood can be changed significantly to create differing aesthetic effects.
Click on each video to view.
Most decorative veneers are FLAT CUT (or flat sliced). This is to say that the knife passes straight over the log, slicing from one side to the other as shown in the illustration. The result is a veneer showing a “crown” (sometimes known as a “heart”). Depending on the growth of the tree this crown may be quite uniform, when it is often known as a “cathedral crown” (as in cathedral windows), or it may be variable or wild. Each can be desirable to the specifier according to the effect required for the finished article or scheme
Normally the area in the middle of the tree (the core) is either rotten or at best defective throughout its entire length and this will be trimmed away to produce some straighter grained material from each side. These veneers are commonly referred to as “halves” or “quarters”.
The leaves of veneer are always kept in sequence as they come off the knife, ensuring ease of consecutive matching throughout.
If there is a requirement for much straight-grain material and the log is deemed suitable for this purpose, then it will be QUARTER CUT. To achieve this the log is marked at the end and then sawn into quarters. Each of these quarters (or flitches) is in turn mounted on the knife at the appropriate angle for the blade to slice across the annual growth rings at roughly 45° to the log's centre. This exposes the radial face of the wood and the total yield will be straight grained, i.e. not showing the crown of the wood. Obviously, the actual straightness of the grain still depends on the growth of the tree throughout its lifetime, and logs chosen for quartering will be carefully selected with this in mind.
TRUE QUARTER CUTTING
Here we see a true quarter sawn oak plank, prized for the rich decorative medullary ray or 'fleck' as shown in the picture. This cut of timber is not only extremely pleasant to the eye it is also the most stable cut for wide planks of oak. When properly dried it will hardly move at all, which means that it is perfect for panel work and fine furniture.
A few decorative veneers are ROTARY CUT (or peeled) in order to reveal the particular growth characteristic that is close to the outside of the log. Bird's Eye Maple, for instance, is almost always cut in this way. In addition some smaller growing species such as Birch are often peeled; otherwise they would be excessively narrow.
Here the log is secured centrally at each end and rotated against the knife blade, the veneer coming off rather like unrolling a roll of paper. After each turn the knife moves closer to the log by the chosen thickness of the veneer being cut. Most veneer produced for the manufacture of plywood is rotary-cut since the resulting extreme wildness of the grain does not matter and, additionally, far greater widths may be achieved by this method. For convenience the veneers are clipped in the width to ensure easier handling.
A variation on full rotary cutting is RIFT CUTTING. Here the log is first cut lengthwise into four, as in quartering, then each quarter is mounted a little off centre on to a staylog machine and rotated against the knife. This produces a growth pattern similar to quartered material but can yield greater widths. However, the stripy effect may also be a little broader than with true quartered flitches and a certain amount of "half-crown" is commonly seen on one edge of some rift-cut veneers.
STAY-LOG CROWN PRODUCTION
Very big logs that are too large for flat cutting into crown veneers in the normal way can be cut first into thirds or quarters before being mounted on to the staylog machine and cutting from the inside to the outside to produce very nice crown grain material in more manageable sizes than would otherwise be possible.
Yet another way of producing crown featured veneers is the HALF-ROUND CUT. This is particularly useful when a log is a little small in diameter for normal flat cutting. The log is first cut through the centre into two halves. One half is mounted on the stay log machine and rotated against the knife so that the arc of the cut produces an increased width compared with flat slicing. However, usually the crown itself has a wider spread and shows less true cathedral pattern.
The versatile staylog machine is also used to cut burrs, the rotation of the log against the knife ensuring burr veneers of a larger dimension than would be the case were they to be flat sliced.