22 



Hardwood Record — Veneer & Panel Section 



June 10, 1919 



logs of various species were received at the Laboratory. 

 The logs were sawn, and materials selected therefrom 

 were kiln-dried under different sets of conditions. Me- 

 chanical tests were then conducted to compare this ma- 

 terial with matched green specimens, and also with 

 matched specimens that had been set aside to air-dry 

 under most favorable conditions. This requires the lapse 

 of considerable time before the final analysis can be made, 

 in order that the material may be properly air-dried. 

 The first and most urgently needed part of this problem 

 has already been worked out, demonstrating the safety 

 of the drying conditions as recommended in the speci- 

 fications, but the second part has not yet been completely 

 solved, and the experiments are still under way. 



Visual Inspection Not Sufficient for Airplane Woods 

 For neadly all commercial uses, it is sufficient that wood 

 be dried without any visible injury or any defect that can 

 readily be detected by inspection. For uses in which the 

 strength requirements are more exacting, such as for im- 

 plements, w^agons, etc., a slight reduction in strength, of 

 I or even 25 per cent, is seldom of sufficient consequence 

 to be considered a serious defect, provided the wood is 

 satisfactory in other respects. Even when strength is of 

 prime importance, as for tool handles, for instance, a 

 serious consequence, such as a casualty, would seldom 



result from failure in this respect. In fact, to the manu- 

 facturers accustomed to handling wood for ordinary pur- 

 poses, and more especially to the lumber dealers who 

 are used to the commercial grading rules and methods 

 of inspection, the selection of wood for airplanes is like 

 learning a new business. It is frequently difficult for them 

 sufficiently to readjust their know^ledge of former methods 

 of inspection to appreciate the significance of the subtle 

 defects which render w^ood unsuitable for airplanes. 



The chief invisible defects not covered by ordinary 

 grading rules are brashness, spiral grain, casehardening 

 (internal stresses), and minute checks produced in the 

 drying that have closed up again and become invisible. 



Methods of inspection, for the detection of these subtle 

 defects are, as yet, by no means satisfactorily worked out. 

 Moreover, inspectors are necessarily inexperienced in this 

 line of work, as such examinations are comparatively new, 

 and no specific tests are known for determining positively 

 whether a particular piece is suitable or should be re- 

 jected. Much depends upon judgment founded on 

 experience, and, as the latter has necessarily been lack- 

 ing, errors have frequently been made. Inspectors have 

 often become alarmed over one or another class of de- 

 fects and have thrown out great quantities of valuable 



a -till 1 1 II II ii} nil //«!/'■ --1 1 



FIG. 



CONDITIONS .SUITABLE FOH KILN-DRYING 3-INCH PL.\NK, CO.XST.V.N'T DE\S- POINT METHOD OF 115° F. 



