2025 Volume 51 Issue 2 Pages 49-60
To expand applicability of ‘deep penetration treatment’, we examined drill machining as an alternative incising method. Various incising method were applied to heartwood of Sugi （Japanese cedar, Cryptomeria japonica） and Karamatsu （Japanese larch, Larix kaempferi） with different drying history, and permeability of an solvent-borne preservative for ‘deep penetration treatment’ was evaluated. Sugi specimen machined with a twist drill exhibited an equal or higher penetration area compared to that with conventional flat blade. In addition, setting the wood moisture content to various level below the fiber saturation point clearly showed inhibition of penetration at moisture content levels in the upper teens （i.e. 16.5, 19.2％） compared to that of 11.3％. This indicates a mechanism that involves liquid penetration occurring either within or near the cell wall. In the liquid penetration for Karamatsu, moisture content dependance bellow fiber saturation point was also observed, suggesting a similar penetration mechanism in Sugi. Moreover, steam drying was found to have potential to improve the liquid penetration in Karamatsu under a certain incising condition, and machining with a twist drill showed equal or higher penetration area compared to that with conventional flat blade. These results indicate drill machining is a promising as an alternative incising method for deep penetration treatment.
