26 



MAKDWUOU KECOKD 



\ovrailM>r lu, 101.%. 



the nrisin«l. Tln>iit' 



pn.. 



eel\» wprv nioro ^U!i 

 ccptible than the in- 

 ner fibers to moisture 

 ehnngns i. e., that the 

 surface rate of dry- 

 i D c or alxHirption 

 was (greater t li it n 

 that of t h e i n n r 

 eells, but tbat the r 

 ner fibers slirnnlc ' 

 timatelr more tli.. 

 the Hurfacc fibers : 

 the ca-v of n r>'>n«i' i 

 section. 



Conclusions 



PI. ATI: V. SKtriiiNS UK Wi:STi:i(N I.AItClI SIKIWINC TIIK KKKKCT of Tin: MICTIIOD Of 

 DUYI.Vi; ON THE SlIHI.NKA<ii:. I-HOM TOl' TO IIOTTOM IN KlTIIKIt nitOL'T TIIK .SKCTIONS 

 AUK KII.N PKIKK. OVKN IHtlKK, ANIJ (JItKEN. 



It develops tlieri' 

 fore, tbat casohard- 



ening is a condition resulting from n difference in stress within ^hc 

 wood. The factor giving rise to these unei|iinl stresse." is n difference 

 in shrinkage of the outer and inner wooil cell!-. .lust why the center 

 of a casehardened l>oard shrinks more than the outside involves two 

 distinct factors, one a "plasticity" effci-t. the other, the intUience of 

 the drying method on the shrinksige of the outer :nid inner cells. 



In the ca.«e of a board not resawcd, the rapidly ilried outer filjers 

 either do not shrink as much normally or are not permitted to shrink 

 while the inside of the board is still above the fiber-saturation point. 

 When the center fillers begin to shrink slowly their "plasticity" 

 materially decreases the ultimate difference in stress l)etween the 

 outer and inner fil>ers. The outer surfaces are said to "set" in 

 an expanded condition, hence the term "ca.sehardening. " This "set" 

 or expanded condition of the outer shell of wood is the resultant of 

 the combined factors of rapid drying rate and plasticity of the hot 

 surface wood which accommodates itself to the still moist center 

 fibers which have not shrunken as yet. One factor aids the other 

 in producing the "set" condition of the surface. 



Now, if a board is resawed while hot and moist inside and dry 

 and "set" outside, the inside slowly dried fibers shrink normally 

 and hence much more than the outer surfaces. The cupping in this 

 case is readily accounted for. Consider that this board is left to 

 come to moisture equilibrium before resawing. As befrre, the outer 

 rapidly dried fibers shrink less than the slowly dried center fibers 

 because of the different drying rates and the effect of the inner 

 fibers, which have not begun to shrink as yet, in frustrating the 

 natural tendency of the outside plastic fibers to shrink. When the 

 inner fibers do commence to shrink, however, the expanded outer 

 shell tends to prevent them from doing so, or in other words, the 

 "set" outer fibers are no longer ]ilastic, so the stresses are reversed. 

 Under these conditions the inner fibers must "set" in a more ex- 

 panded condition than if the board were at once resawed, in which 

 case the moist, plastic, inner fibers were not kept from shrinking 

 by the "set" outer shell. In the light of these facts it is evident 

 why the resultant difference in stress is greater when a board in 

 which the moisture distribution is unequal is resawed while moist 

 and hot, than when allowed to come to moisture equilibrium and then 

 resawed. 



The degree of casehardening of the different species of wood under 

 similar drying conditions depends undoubtedly on the ability of the 

 outer and inner fibers to accommodate themselves to the different 

 stresses created by the unequal shrinkages of the outer and inner 

 fibers. Some of the hardwoods, especially oak, fail to accommodate 

 themselves to these stresses which are very great, and become surface 

 checked and honeycombed as a result. The fibers of other species 

 are not ruptured by the stresses, which are comparatively small. In 

 such cases no checking or honeycombing may occur although the 

 difference in stress may persist to a marked degree. 



These different stresses, which remain after the moisture has 



reiichcd equilibrium, 

 lire the rnuM of 

 ' ' |>iTninnenl c a se • 

 li:irdi>ning. " The 

 • liffcrenre of moll- 

 turo content l>otwe<'n 

 the outer and inner 

 portion* is fre<|uent- 

 ly called canchnrden- 

 Ing but is only a 

 Irniporiiry factor, 

 here denignnted U 

 ' ' ti-uipornry i- a it o • 

 hardening. " 



Thus at least four 

 distinct factors un- 

 derlie tiie conditions 

 which exist in case- 

 hardened wood. The 

 first is une((ual mois- 

 t u r e distribution, 

 bringing into play the different stresses an<l resulting "setting" 

 of the outer surface, accompanied by surface checking, followed by 

 reversed stresses and internal tension, attended by honeycombing. 

 This condition is more or less temporary. We shall give second place 

 to the unequal shrinkage of the inner and outer fibers caused by the 

 surface drying more rapidly than the center. This is clearly u [ler- 

 m.inent effect. Third in importance is the slight apparently perma- 

 nent difference in hygroscopicity between the outer and inner fibers. 

 Let us place the difference in sensitiveness to moi-'in'- ■•Imiiu"'" Ix- 

 tween the outer and- inner fibers fourth and last. 



National Efficiency Productive 



We have had the loss of power in friction figured out for us on 

 ]>retty fine, hair splitting lines, and have had demonstrations of the 

 wasted energfy in a machine running empty, but have yet hardly 

 touched the subject of the personal energy and motions wasted in 

 handing machinery, and the material worked on the machines. We 

 know that the secret of capacity in a sawmill is to keep the saw- 

 in the log as continuously as possible. Here is where we frequently 

 have one of the plainest cases of wasted motion and energy. 



.\ sawyer of the rambunctious kind will run his carriage back from 

 two to four feet farther than is necessary, bring it to a sudden stop, 

 and perhaps jerk it back a time or two, manoeuvering for position 

 to turn his log. lie works himself and the carriage men hard, and 

 looks to be tearing the bone out of things, but often he makes less 

 lumber than the quiet man who makes no unnecessary moves of 

 either himself or the carriage, but stops easily at the right place 

 every time, keeps the saw in the log, with but little lost time or 

 motion, and doesn 't seem to be rushing things at all. 



In the planing mill and factory we have in different form some 

 of the same waste of motion and energy. One man will make half 

 a dozen different moves in picking up a board and putting it in 

 a machine; another will have a truck containing his material bo far 

 from the work that he must take two or three useless steps each 

 time he gets .a fresh piece; another will get stock on the wrong 

 side. And so it goes. All around we keep on wasting personal mo- 

 tion and energy, as well as let machines run idle and waste power. 



There are what we call efficiency experts studying and )>ointing 

 these things out now, and often reducing them to such hair splitting 

 extremes that they liecome so aggravating as to interfere with their 

 usefulness. That is what generally happens when the pencil ex- 

 perts get to work on an idea of this kind; they chase into so many 

 nooks and corners, and pick up so many picayune points that they 

 themselves often fall into the error which they are trying to cor- 

 rect. Yet, taken rationally, good work in efficiency can be done by 

 making a study of the wasted energy of unnecessary motion. .Study 

 not only your own inovenienis, but those of the stock you are hand- 

 ling. See how many of them are really prodiK-tivp of actual results, 

 and how nianv are not. 



