W. DALE GREENE [+]
Production and quality measures were collected and analyzed for a new chain-flail delimbing machine, Chambers Delimbinator, on two operations in central and southwestern Georgia. The first operation, Logger A, used two skidders and one loader while the second operation, Logger B, used two skidders and two loaders. Logger B with the lower cycle time and larger piece size produced an average of 57.4 tons per hour, while Logger A produced an average of 39.2 tons per hour. With defects defined as a branch greater than 1 inch in length and 1 inch in diameter the Chambers Delimbinator produced similar delimbing quality for both logging operations with 5.7 defects per stem for Logger A and 7.0 defects per stem for Logger B. The Chambers Delimbinator is well suited to delimbing stems produced from first thinnings of loblolly pine (Pinus taeda L.) plantations.
Delimbing is an essential step in the conversion of standing trees to roundwood products. The objective is to remove limbs flush with the bole of the stem, leaving no protruding stubs, without breaking sections of the bole at the base of the limb. Delimbing quality standards are typically higher for sawlogs and veneer grade logs than for pulpwood. However, poor delimbing quality can potentially reduce the quality of chips produced by increasing the percentage of bark, fines, and oversized and undersized chips. Delimbing accounted for 30 percent of the cost of putting radiata pine on board trucks in New Zealand  while delimbing and bucking together accounted for 24 percent of on-board costs in Montana .
In the southern United States, the most popular delimbing method uses the delimbing gate . Grapple skidders back trees into this steel grid and the limbs are broken off as the stem is pushed into it top first. Gates are simple, inexpensive to purchase, require little or no maintenance, and effectively handle multiple stems. However, they often do not remove limbs flush with the bole of the stem, thus requiring that the job be finished with a chainsaw or another delimbing method. They often break the tops of small trees and delimbing quality suffers when the size of the tree is substantially smaller than the grid openings. With the young trees typically removed in first thinnings, limbs are often very flexible and are not as effectively broken by the gate as are more mature trees from other types of harvests.
Pull-through delimbing machines used in conjunction with log loaders are also now a common delimbing method in the South . These hydraulically operated devices utilize an inverted grapple with delimbing knives and a topping saw. The loader places stems in the grapple; the grapple arms (knives) are closed around the stem; the loader pulls the stem through the grapple, severing limbs as they strike the knives; and the topping saw is used to remove the unmerchantable top when delimbing reaches the desired top diameter. Most of these units have been purchased to supplement, not replace, delimbing gates. In...