Lathe check formation and their impact on evaluations of veneer-based panel bond quality

During the peeling of veneer, lathe checks as deep as 70 to 80% of the veneer thickness are formed. This study showed that during adhesive testing according to EN 314 deep lathe checks in birch (Betula pendula Roth) veneer significantly reduced the shear strength of phenol-formaldehyde (PF) bonded plywood, even though these checks are not mentioned in the standard. In addition, we show that specimens tested open can fail by a different mechanism than those pulled closed, especially when checks are deep. Lathe checks were also shown to influence bond strengths when using the Automated Bonding Evaluation System (ABES). These findings stress the importance of measuring lathe check depth and considering the orientations of checks during testing to get a better understanding of bond quality in veneer-based products.