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The rodding mentioned above for reinforcing deep cavities is called "wood screw" and it comes in various diameters up to two inches. It is iron bar, threaded its whole length, which is screwed through opposed holes in the hollow tree and sawed off flush to the bark, which will grow over the ends. When wood screw is used to reinforce a weak crotch, the crotch should first be drawn together tightly by a "come-along" (interlooped rope sling, or noose) rigged high up in the members forming the crotch. This is necessary because the bar's threading, being continuous, has no pulling power. Turned with a pipe wrench through holes bored slightly smaller than its own diameter, the rod only holds fast in whatever position it is left. More positive in their action, but more expensive, are bolt-and-nut assemblies which must be measured, cut, and threaded to fit each situation. And the nuts, with elliptical or diamond-shaped washers, must be countersunk into the bark to get them healed over properly. But bolts are best for mending split limbs, which they can draw together. The optimum position for rodding is about twice the smaller member's diameter above the weak crotch. In case of dire weakness, put one or even two more rods a like distance farther up. (Always coat with tree paint any metal put into living tree tissues. This goes for drain tubes or pipes, too, which need not be driven more than three or four inches into their holes.) |
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