How to Cut Tree Disks Without Formation of Checks

Crosscutting of tree stems relieves longitudinal growth stresses and converts them into tangential tension forces near the ends of the logs. Tree disks cut from the ends of logs therefore usually develop heart checks. The level of tangential tension is calculated for various tree section lengths by a finite-element method; it is highest near the pith at log ends where heart checks start. In sections shorter than two diameters, tension decreases as section length decreases, approaching zero below 1/4-diameter length. Cutting logs first into short and then dividing the sections into disks prevents many heart checks. Formation of heart checks can be prevented entirely by cutting many disks simultaneously out of one log. Circumferential bands stretched around the log end prevent checks, provided the old and the new ends are always banded from beginning of cutting until the disk is separated. The bands have to be wide and must be stretched with so much force that the method is feasible only up to diameters of 2 feet in dense hardwoods and roughly 3 feet in low density species. At temperatures below freezing, water migrates out of moist cell walls and freezes in cell cavities. The resulting “cold shrinkage” is higher tangentially than radially and causes differential shrinkage stresses which cancel primary growth stresses. Therefore, frozen logs check little or not at all when crosscut. As cold shrinkage increases with decreasing temperature, disks are best cut from very cold logs. Between zero and -20?F depending on diameter and tree species, very likely no crosscut checks will develop. Of course, not all cuts have to be made at low temperatures; it is sufficient to divide the cold log into 1/4-diameter sections and to cut the disks from the sections at temperatures above freezing.

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