August 10, 1917 



Hardwood Record — Veneer & Panel Section 



31 



Shrinkage and Trimming Allowance 



Misunderstandings Often Result from Changes Due to Seasoning 



ETWEEN THE TIME of measuring the log or 

 block by the best devised wood measure rule 

 and the final dried finished product there are 

 two items of loss which in the aggregate make 

 up big totals that are only of late getting the recognition 

 they should have. TTiese items are the shrinkage in 

 drying, and the allowance for trimming to size. 



Our measuring system in its original inception was 

 based upon the number of square edged inch boards 

 that could be produced from a log. These, of course, 

 were green w^hen produced, and no thought seems to 

 have been given the shrinkage in drying in developing 

 the system of measurement. 



In the cutting of rotary veneer the percentage of 

 shrinkage in drying is even greater than lumber because 

 most wood shrinks considerably more in the direction of 

 the width of rotary cut veneer than in the direction from 

 the heart to the outside of the log. This shrinkage loss 

 is enough in cutting gum, for example, that should a 

 man measure up 1 0,000 feet of surface measure rotary 

 cut gum while it is green he would probably find after 

 drying and sorting that he had only 9,000 feet. There 

 is a loss that must be taken into the accounting system 

 somewhere, somehow, and along with it the other loss, 

 that of trimming to exact dimension. 



It is a reasonable presumption that a manufacturer 

 in cutting rotary stock to dimensions will make his 

 measurements on the basis of its condition at the time 

 of the cutting dimension. If the stock is thoroughly 

 dry when it is clipped out to the dimensions called for, 

 then the shrinkage loss as well as the trimming v^^aste 

 has been absorbed by the manufacturer. If, however, 

 it is only partly dried, as is often the case, the shrink- 

 age has hardly begun and the shrinkage loss will fall 

 upon the buyer. 



The gum folks specify that stock must be dried so 

 that it v^rill not mould or damage in transit. This is 

 really indefinite and if stock is shipped as soon as it is 

 dry enough to pack vvfithout moulding, that is with a 

 little air drying or a very slight kiln drying, it has hardly 

 begun its shrinkage. Experiments have proven that 

 most of the shrinkage in lumber stock takes place in 

 the final process of drying out and that the shrinkage 

 is very light in the early preliminary stages of drying. 

 Therefore if veneer stock is clipped to dimension before 

 it is thoroughly dry, then it will shrink from 5 to nearly 

 I per cent in width in the final drying out. 



This means that if the original cutting dimensions are 

 those wanted for finished stock, the allowance must be 

 pretty liberal for shrinkage. If the original dimensions 

 given are to include room for final trimming to rize the 

 allowance must not only provide this but also the shrink- 

 age loss. Tak'ng it altogether, there is a considerable 



item of waste when we combine the shrinkage in the 

 final process of drying out and the allowance for trim- 

 ming. So far there has not been devised any general 

 method for preventing shrinkage loss. Maybe some day 

 we will devise a system for drying treatment which will 

 fill the pores of the wood with something to prevent 

 shrinkage and veneer stock will retain its normal dimen- 

 sions. That, however, is merely a possibility of the 

 future. At the present time there is a shrinkage loss 

 and the allowance for trimming. 



If dimension stock is to be cut at the veneer mill to 

 exact specifications given and the buyer must pay for 

 the full dimension, and make provision therein for 

 shrinkage and trimming, and absorb all this loss, it 

 means that the buyers will soon be giving very searching 

 attention to the matter of reducing the allovk^ance for 

 trimming to the lowest possible minimum. This will be 

 w^ork that has long been needed and should have been 

 undertaken voluntarily. So long as the cutters of 

 veneer and lumber wrere willing to furnish extra width 

 and extra length for trimming, the buyer w^as not con- 

 cerned about the matter of making this extra allowance 

 the smallest practical, but rather inclined toward getting 



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