A comparison of kiln-drying schedules and quality outcomes for 4/4-thickness black cherry lumber sawn from small-diameter logs

With high stumpage prices, many sawmills are interested in the feasibility of processing smaller diameter hardwood logs. Most of these mills do not know the lumber yield, lumber grade, or cost of processing these logs. In this project we investigated the impact of alternative dry kiln schedules on the grade yields and defect occurrence in lumber sawn from small-diameter (logs with small-end diameters of 11 inches or less) black cherry (Prunus serotina Ehrh.) logs. The position within the log from which each board was sawn was mapped in relation to the profile of the logs. Every board was examined for end checks, surface checks, shake, twist, bow, cup, crook, and assigned a predrying grade. The lumber was dried using a conventional black cherry kiln schedule published in the Dry Kiln Operator's Manual (Simpson 1991) and two modified kiln schedules designed to dry lumber under milder drying conditions compared to the conventional schedule. The modified kiln schedules maintained equilibrium moisture content (EMC) conditions that were comparable to those of the conventional kiln schedules for each of the drying steps. After drying, each board was again examined for end checks, surface checks, shake, twist, bow, cup, crook, and assigned a postdrying grade Modified kiln schedule #1, in which the final dry-bulb temperature was lowered 20°F from that of the conventional schedule, provided the best drying results in terms of the reduction in defects and minimization of grade loss as compared to the conventional (T4-D8) cherry schedule. Overall, for all three kiln treatments, lumber grade yield increased with increasing log diameter and log grade, and it improved in the direction of pith to bark. This study will provide the hardwood products industry with a better understanding of the feasibility of and approach for processing lumber from small-diameter black cherry logs.