## 1 Introduction  
The conversion efficiency of sawlogs into lumber is one of the most important business and production indicators for the wood industry. Resource saving production is becoming a more and more important issue, not only for environmental reasons but also for financial reasons, considering that the costs of raw materials significantly affect the costs of lumber production. The log conversion efficiency strongly depends on the log diameter and its length, the usual shape deviations (e.g., taper and curvature), the log quality (cracks, discolorations, fungal and/or beetle attack), the kerf width, the condition and maintenance of the grading and cutting equipment, the sawing pattern and the required product mix, the sawing method, etc. [1]. The target for sawmills is to obtain the highest percentage of lumber from each cut log, at the best possible quality, so as to ensure a high profit. Cutting tools and machinery must be up-to-date to achieve maximum yield and to supply the further processing chain with the best raw materials. Next to optimal tools and tool geometry (e.g., optimal sawblade thickness), perfectly configurated production lines are needed. Three-dimensional-infrared scanners and X-ray computed tomography [2] are used to find the maximum information about the raw material and to determine the optimal position for the logs before entering the cutting line. In this way, it is possible to identify wood defects (e.g., cracks, resin pockets, knots, and shape deviations) before the cutting processes and to establish the log position that would eliminate them but still reach the highest possible yield and targeted product quality. The visual appearance of the final wood surface is also important and requires the best quality logs and a suitable cutting pattern. The problem is that these logs are not always available in large quantities. Forecsters must manage to harvest all logs damaged by beetles, wind, and snow, while fresh and healthy logs are becoming increasingly rare. Thus, solutions for increasing log conversion efficiency represent a topic of great interest. At present, big size sawmills do not take into account the taper value when presorting the logs. With strongly tapered logs this leads to significant volume loss. Experimental tests previously performed [3] showed that the conversion efficiency of processing fir roundwood into debarked sawlogs ranged between 67% and 85%, the lowest values being recorded for the most tapered pieces of roundwood (1.6 cm/m). At present, sawmills do not account for the taper value of the logs. This means that the logs are sorted into a box depending only on their quality, length, species, and top diameter, leading to an incomplete vaporization of the wood volume of tapered logs when the tapered part falls into the \"firewood\" box. Considering the above-mentioned factors, the main objective of the present paper was to evaluate the effects of edge-gluing together, under an angle around 45\({}^{\circ}\), the mirrored sideboards from tapered logs (having variable width along their length), after a double rotation, in order to valorize this wood as well. The target is for structural uses within laminated products for construction (e.g., CLT or Glulam). Structural wood elements, such as the ones used in construction or mines, are frequently subjected to static bending stresses that may be concentrated or distributed. An increasing load leads, first, to the bend of the element and, when a certain critical value is exceeded, the element breaks. Therefore, with structural elements, it is essential to know the limits of the material in terms of the modulus of rupture in bending (MOR) and the modulus of elasticity in bending (MOE), which are closely correlated with the material density (\(\rho\)), one of the most quality indicators of the wooden material. These three properties were chosen to be determined within the present research for this reason.