20 



HARDWOOD RECORD 



March 10, 1917 



surface and interior of the wood tend to shrink unequally for two 

 reasons. As has already been stated, the faster wood is dried 

 in dry air the less it shrinks, and the slower it is dried in moist, warm 

 air the more it shrinks. With this fact in mind, it is clear that if the 

 surface of the lumber is dried much more rapidly than the interior, 

 it will tend to shrink less than the interior. As the center of the 

 board dries slower tlian the surface, it tends to shrink more than 

 the surface. Therefore, it is evident that a tendency to unequal 

 shrinkage exists. 



The vital fact causing the unequal shrinkage is the resistance to 

 surface shrinkage offered by the interior of the board after the 

 surface has started to shrink and before the interior has commenced 

 to shrink. This resistance reduces the surface shrinking, causing 

 the surface to "set" in an expanded condition. It is during this 

 stage of the drying process that surface cheeks appear, (see 2, 

 Fig. 1 — casehardcuing). When the interior begins to shrink, in 

 turn, it tends to shrink more than the set surface, puUing away 

 from the outer shell and causing the interior checks, commonly 

 termed honeycombing (see 3-4, Eig. 1 — Casehardening) . During this 

 final stage in the development of casehardening the surface cheeks 

 invariably close up, sometimes so tightly that they can not be seen. 

 ■ Lumber may be severely casehardened without being either surface 

 checked or honeycombed. In such cases, resawing must be resorted 

 to in order to determine the degree of casehardening. At 5, (Fig. 1 — 

 Casehardening), a resawed board shows no casehardening or stressed 

 condition because the halves remain flat after sawing. At 6, how- 

 ever, the characteristic cupping action of a resawed casehardened 

 board is indicated. The reason for this action is that the surface 

 is held in compression by the tension of the interior. Resawing 

 relieves the surface compression, and the cupping results. This 

 cupping may occur on the resaw or upon subsequent drying of the 

 exposed interior. In either case, it is proof of casehardening.* If 

 a casehardened board, whose interior and surface moisture contents are 

 say thirty -five and fifteen per cent respectively, is resawed, the halves 

 wiU cup outward from the resaw as shown at 7. This is explained by 

 the fact that under these conditions of moisture distribution the 

 tension of the surface tends to compress the interior. Upon subse- 

 quent drying th-3 cupping reverses to an aggravated degree. This 

 gradual reversal of stresses in the drying of casehardened lumber 

 is clearly illustrated by the action of the resawed section shown 

 in Fig. 2. 



The purpose of this paper is to present methods of determining 

 the conditions in lumber, rather than to advocate cures for those 

 conditions which constitute defects. However, casehardening is so 

 serious a defect that we believe a word in regard to a method of elim- 

 ination may not be out of place. If casehardened lumber is steamed 

 for the proper period at the close of the drying operation and then 

 dried off, the stressed condition may be entirely relieved and all case- 

 hardening eliminated. It is only necessary to adjust the length of 

 the steaming period according to the severity of the casehardening. 

 It is also essential that the steam circulate through aU portions 

 of the piles of lumber in a uniform manner. This method has 

 been used with complete success in the kiln-drying of inch red gum 

 lumber and black walnut green from the saw. Figure 3 shows the 

 results of such a process in the case of inch air-dried red gum 

 lumber. It is important to note, in this connection, that if the 

 steaming period is too long or severe, the casehardening is actually 

 reversed. 



Brittleness 



Lumber may be inherently brittle or rendered so by drying at too 

 high temperatures. Too long exposure to ordinary kiln temperatures 

 will also produce this effect. The change is usually accompanied by 

 a darkening in color whicli serves to prejudice one against it for 

 certain purposes. Where brittleness is not a serious defect, this 

 method of overheating wood may be resorted to in order to darken it 

 and thus enhance its natural beauty. 



At present, many users of lumber associate kiln-dried lumber with 



brittleness. This is so because of the many improper methods of 

 kUn-drying now in use. If the proper circulation of air, at the proper 

 temperature and humidity, is maintained for the necessary time only, 

 there is no reason why kiln-dried lumber should be unduly brittle. 



No very definite simple test may be given for brittleness because 

 it is one of those comparative conditions which the experienced user 

 determines by bending and breaking. The toughness or ' ' life ' ' of the 

 lumber can be lost by improper methods of drying. 



New Zealand Teak 



Practically every country in the world . lying within the tropics 

 produces a wood called mahogany in the trade. The same may be 

 said in reference to teak wood. Most timber dealers and wood users 

 know the true teak wood of commerce which comes from India, Cey- 

 lon, Burma and Siam, but they are less familiar with the so-caUed 

 African, West Indian, Brazilian and New Zealand teaks. The New 

 Zealand teak (Vitex littoralis) locally called puriri is an important 

 timber which has been known to European wood users for more than 

 one hundred years. While it is at present only rarely shipped into 

 England and the United States, it is of interest to the trade because 

 the wood is exceedingly durable and wag used for a long time as a 

 substitute for the live oak. 



New Zealand teak is not confined to New Zealand, where it has 

 been exploited for so many years, but it is common also in the Philip- 

 pines and other groups of islands in the South Sea. It is found in 

 nearly all forests along the coast where the soil is permanently moist. 

 While this wood has been practically exhausted in New Zealand, it 

 can be seen from its extensive distribution that vast quantities of 

 the timber are procurable in many of the other South Sea islands 

 where the timbers have hardly been touched. 



The nearly yellow sapwood in mature trees varies, from two to 

 three inches in width, the heartwood, which contrasts strongly with 

 the sapwood, is very dark brown and is exceptionally durable. It 

 is considered the most durable wood in the region where it is grow- 

 ing. The wood is heavy (about seventy-five pounds per cubic foot) 

 hard, strong, close and fine-grained, and the logs which come to mar- 

 ket are usually from sixteen to twenty feet long and about sixteen 

 inches square and free from defects. The wood takes a splendid 

 polish and contains a coloring substance suitable for dyeing wool 

 and cotton. It is one of the most useful timbers, and is now employed 

 extensively in shipbuilding, for railroad ties, posts, piles, and for 

 the frame work o^ houses and the foundation of large structures. 



There are just as many advantages in a smooth shop or factory 

 floor as there are in some of the machines and appliances that sales- 

 men give you a smooth talk about. The difference is we don't have 

 them pointed out to us so often. 



Speaking of woodworking machines in which the user has a 

 chance to select from a wide variety of offerings, what about mold- 

 ers? There are inside, outside, combination and a multitude of 

 varying designs, as well as different sizes to select from. 



Dry hickory flitches or dimension stock make up a good hard- 

 wood item these days — the call for hickory being quite brisk. 



A mah who has tried many methods of fastening leather covers on 

 pulleys, says the only sure way is to rivet them on, heads of rivets out. 



Locating the lumber yard so that it is burdensome to get stock into 

 the mill or factory is a serious mistake sometimes made. Saving 

 energy here is just as important as saving time and energy in machine 

 work. 



•See article by H. D. Tiemann, "Problems in Kiln Drying Lumber," Lum- 

 ber World Review, September 25, lOl.'j. 



A really good machine operator will display impressive qualities of 

 knowledge and workmanship, no matter whether he is running a poor 

 machine or a good one; and if it is a poor machine he wiU soon 

 make it better. 



