PRACTICAL TREE SURGERY 389 



be bolted every 18 to 24 inches. Often a single bolt can be placed 

 so as to support both sides (Fig. 306 B). In certain cavities it rnay 

 be necessary to place bolts at different angles (Fig. 306 C). In any 

 case a strip of uninjured cambium at least an inch wide should be 

 left between the edge of the cavity and the bolt. On medium- 

 sized trunks, after deciding where the bolts can most efficiently be 

 placed, a very sharp half-inch bit, sufficiently long to reach through 

 the trunk and the cavity, may be used to bore the hole for the bolt. 

 On large, heavy trunks a larger bit should be used. 



Heavy oval or round iron or steel washers, about three times the 

 diameter of the bolt, should be countersunk into the wood by care- 

 fully cutting away the bark at both ends of the hole with a sharp 

 gouge or a chisel (Fig. 306 B, C, D). The washers should be heavy 

 and ample, but not so broad as to necessitate cutting away a large 

 piece of bark. In most trees when round washers are used it is 

 advisable to have this countersunk area somewdiat pointed above and 

 below the washer, to hasten healing. By holding the two washers in 

 place, the length of the steel machine bolt can be determined by 

 measuring through the hole. 



The bolt must be thick enough to fit snugly in the hole and should 

 project beyond each washer for at least J-4 inch. The thread at 

 each end of the bolt must be sufficiently long to permit drawing in 

 the sides of the cavity a little, as the nuts are screwed up against 

 the washers. A chamfered single-headed bolt may be used, if pre- 

 ferred. Before the bolts are finally put in place the countersunk 

 cuts and bolt holes should be tarred or crei'Snted, and after the bolts 

 are in place all exposed parts of the bolts and nuts should be tarred. 



All split cavities must be securely bolted, particularly near the 

 upper part. If the split comes from a crotch, all decayed and dis- 

 eased wood should he removed from the split and creosote and tar 

 applied, after which it may be bolted just beneath the crotch, so as 

 to close the crack or at least bring the parts back to their normal 

 position in case decayed matter has been excavated from the crack. 

 If the split is a recent one, a washing of creosote only will usually 

 be sufficient before drawing the sides together with bolts. 



Under certain conditions, particularly in large trees, it may be 

 necessary to use a rope and tackle blocks to pull the limbs together 

 some distance above the crotch, in order properly to close the crack 

 before bolting it. When tackle blocks arc used, care must be taken 

 to have an abundance of bagging or other padding between the bark 

 of the limbs and the encircling ropes. All exposed edges of the 

 crack must now be covered with thick tar. Limbs above split 

 crotches may be guyed. If there is a cavity in the crotch, the limbs 

 above it must be guyed before this cavity is filled. 



297. Nailing. — If the cavity has a comparatively large opening or 

 has little or no undercutting, it is the custom to drive flat-headed 

 wire nails into the wood in the interior in order to hold the cement 

 filling firmly in place. In medium-sized cavities nails 2'/; or 3 inches 

 long are usually driven into the wood for about half their length 



