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This work describes distortion (bow, crook, twist, cup) and the formation of visible cracks in green and seasoned timber of Scots pine and Norway spruce. Distortion and crack formation have been evaluated according to the original location in the cross section of the log. The purpose is to describe differences in distortion and crack formation between sawn timber taken from star sawing and from traditional sawing patterns. Bow and crook develop in the green timber immediately after sawing as a result of growth stress release. Drying and conditioning in general lead to a marginal increase in bow, but crook may show a large percentage increase depending on the location of the wood in the cross section. Twist and cup do not occur directly after sawing, but arise during seasoning of the wood. In sawn wood, the juvenile wood has a major influence on the twist. This means that timber sawn close to the pith shows a greater twist than timber sawn away from the pith. This is a consequence of the fibre orientation in this timber. Cupping increases with decreasing radius of curvature of the annual rings in the cross section of the timber. Cracks occur in timber before seasoning. The pattern of crack formation is the same in both pine and spruce; timber sawn close to the pith or with pith enclosed exhibits a considerably larger number of visible cracks than timber sawn away from the pith. Cracks occur mainly on surfaces orientated to the pith, a fact that becomes clearer when timber is observed close to the pith. Seasoned star-sawn timber with a rectangular cross section has bow and crook of the same extent as or less than that of timber sawn according to traditional sawing patterns. Seasoned star-sawn timber with a triangular cross section has high bow, but the crook is low. Star-sawn timber does not show any cup and has a good shape stability according to the geometrical shape in the cross section. It also has a very small twist and shows very few visible cracks after seasoning.

A new manufacturing system, the PrimWood Method, has been proposed to improve the utilization of wood. A basic concept within this method is the sawing pattern called star-sawing, which produces timber with both rectangular and triangular cross sections. This method facilitates an efficient production of radially sawn timber with vertical annual rings, without juvenile wood. The sawn timber produced in the PrimWood Method is used to produce high quality, knot-free solid wood panels with vertical annual rings. In this process, part of the timber is finger-jointed to form knot-free lengths which are glued together into a block. This block can then be divided according to thickness into thinner panels with vertical annual rings. The PrimWood Method has been tested in an industrial plant. The manufacturing system was designed for a sawing capacity of about 30,000 m3 logs, which corresponds to 16,800 m3 of star-sawn timber per shift per annum. The production of solid wood panel was then designed to give a volume of 5,800 m3 per annum.

A method is presented for the gluing of star-sawn triangular profiles of pine (Pinus silvestris L.) into form-stable wood products with vertical annual rings. The triangular profiles are free from pith and from most of the juvenile wood.The method is based on dried and conditioned triangular profiles. Undesired defects are removed and the wood is finger-jointed into long lengths. In the finger-jointing, consideration is given to the appearance and annual ring orientation of the jointed materials. After the jointing, the triangular profiles are planed and glued into rectangular blocks with vertical annual rings. These blocks can then e.g. be used as construction beams or be sawn up into solid wood panels.A pilot plant has been built for the manufacture of knot-free solid wood panels based on the proposed method. Results show a total volume yield of 53.8%. Three critical production stages can be distinguished: removal of knots and defects, planing, and division of blocks into boards. These three operations are together responsible for more than 93% of the total losses in the manufacture.The removal of knots and defects meant a volume loss of 12.8%. 13% of the manufactured units were 2.1 m long without finger-jointing and free from knots and other defects. The average length of the remaining pieces used for finger-jointed units was 0.41 m. Diese Arbeit beschreibt eine Methode zum Verleimen von sterngesägten Dreikantprofilen aus Kiefernholz zu formstabilen Produkten mit stehenden Jahrringen. Die Dreikantprofile sind frei von Mark und überwiegend auch von juvenilem Holz. Verwendet werden getrocknete und konditionierte Profile. Unerwünschte Holzfehler werden ausgeschnitten. Danach werden die Werkstücke durch Keilzinkung längs verleimt, wobei auf das Aussehen und die Ausrichtung der Jahrringe geachtet wird. Nach dem Hobeln werden diese Dreikantwerkstücke zu rechteckigen Blöcken mit stehenden Jahrringen verleimt. Die Blöcke können z.B. für Konstruktionszwecke verwendet oder zu Brettern oder Platten aufgesägt werden. Im Pilotmaßstab werden inzwischen astfreie Platten nach dieser Methode hergestellt. Insgesamt wird eine Volumenausbeute von 53,8% erzielt. Drei kritische Produktionsschritte sind dabei zu beachten: Entfernen der Äste und sonstiger Fehler, Hobeln sowie Auftrennen in Bretter. Bei diesen drei Produktionsschritten fallen über 93% des Massenverlustes an. Das Entfernen der Holzfehler führt zum Verlust von 12,8% des ursprünglichen Volumens. 13% der Werkstücke hatten eine Länge von 2,1 m (astfrei, vor dem Verleimen). Die durchschnittliche Länge der übrigen zum Verleimen verwendeten Stücke betrug 0,41 m. Upprättat; 1998; 20140903 (dicsan)

The influence of annual ring orientation on strength and dimensional changes during moisture variation in finger joints.