Wood Finger-Joint Strength as Function of Finger Length and Slope Positioning of Tips

Besnik Habipi, Dritan Ajdinaj

A study was carried out to analyse the relation of slope positions of fingers tips and finger length with regard to bending strength of poplar (Populus alba L.) and silver fir (Abies alba Mill.) finger joints, bonded with polyvinyl adhesive. There were produced three finger lengths, 6, 10 and 14 mm, as well as four series for each finger length and species, with 16 test pieces for each series. The first one with tips in straight vertical line and three others with tips in slope direction, respectively with slope angle 10°, 20° and 30°, referring to the first one direction. With regard to fingers with tips in slope position were respected the same values of length and pitch. Modulus of Rupture (MOR) and Modulus of Elasticity (MOE) of finger joints were measured according to norms ISO 13061-3 and ISO 13061-4. Results showed that static bending strength was strongly influenced by the length of finger. For longer fingers the strength resulted higher. This relationship was referred to the rate finger length/pitch from 1 to 2.3. With regard to position of fingers tips, the angle 10° showed the best performance for all three finger length taking into account. By the other hand, modulus of elasticity wasn’t affected in a distinct manner neither by the slope angle of fingers tips position, nor by the finger length. We can say that “scarf-finger joint” with slope angle of 10°, has a better performance with regard to MOR in static bending strength, presenting so a good opportunity for industrial application.