September, 10, 1921 



HARDWOOD RECORD 



27 



Ou btluill' of one of its readers Hahdwouu Hi;cukd recently 

 secured a compendium of expert information on the practice of 

 cutting t(f allow for shrinkage of hardwood lumber through ten 

 niontlis' air-drying. This information disclosed that cutting prac- 

 tice Is not uniform with the various mills, and that there is also 

 a wide difference in tlie shrinkage of different species of hardwoods. 



On the assumption that the data involved in this question is of 

 broad general interest it is herewith passed on to the trade, some- 

 what in the (iriler ill which it developed. First the — 



QUERY 



What thicknesses are I'dUKli, iiir-diicil luinhviiuils supposed In l)c in 

 1". 1V4". 1V4". '■^" when ten months' air-drieil or suitahli' fur putting in a 

 dry kiln? Also what thickness after kiln drying? 



Then the— 



ANSWERS 

 From Lumbermen 



Wc endeavor to follow the National Hardwood Lumber Associa- 

 tion inspection rules as closely as possible. By that v;e mean : .\11 FAS 

 lumber plump thickness. Cuttings to be full thickness ou common lumber, 

 taking advantafie of the differential permitted in the rules. We havi' 

 never made any distinction in the thickness in shippin)^ lumber for kiln 

 drying. We are not familiar with the shrinkage developing in kiln ilrying 

 hardwood lumber. 



We believe stock should be sawn sufficiently thick so that it would be 

 full thickness when ten months' air-dried, that is, when sawn green it 

 should be about 1/16" full, so that it will dry out full thickness after 

 being dry. We don't really know what the thickness of the stock is after 

 it comes out of the kiln, but assume that it shrinks anywhere from 

 1/32" to l/(i4". 



We cut our 1", l^i", I'i;" and 2" lumber l/ir>" heavy. It dries out. to 

 become properly air-dried, a little less than G per cent, and leaves the lum- 

 ber sufficiently thick to surface to the standard thickness of surfaced 

 lumber that is: 4/4" to 13/16", 5/4" to 13/32", 6/4" to 111/32", 

 S/4" to 1 3/4". , 



We imagine that the shrinkage and dry kilning of air-dried stock will 

 be somewhere between 4 anil 5 per cent, probably nearer 4 than 5 per 

 cent, but this last statement is made without claiming to be accurately 

 informed. 



From Dry Kiln Companies 



Your question can only be answered in a general way, because it is 

 not specitic enough lo permit an accurate answer. For example, saw-ing 

 practice varies consitlerably. The variation in the natural shrinkage of 

 illflferent hardwoods is very great. You do not specify whether the lumber 

 is quarter-sawed or plain-sawed nor do you specify the time of the year 

 the lumber is cut. .\11 of these factors affect the shrinkage to a great 

 extent. 



In general, all hardwoods do not l>egin to shrink at all or apprecial)ly 

 until they have dried below 30 per cent moisture, or until all of the free 

 water has been dried out. Furthermore, (piarter-sawed lumber shrinks 

 twice as much in thickness as plain sawe^l. Inuring the best drying ten 

 months (»f the year 4/4" hardwoods will dry to about 25 per cent moisture, 

 and the shrinkage will be api>roximately IG'% per cent of the total shrink- 

 age in thickness. Taking sugar maple as an example, the approximate 

 shrinkage within ten months' air-drying will be approximately as follows: 



I'laln Sawed Quarter Sawed 



4/4" 008 inches .015 Inches 



5/4" 01 inches .019 inches 



6/4" 012 inches .023 inches 



8/4" 016 inches .031 inches 



With the same nmterial kiln-dried to 5 per cent moisture, shrinkage 

 would be approximately as follows: 



Plain Sawed Quarter Sawed 



4/4" 04(Hnche6 .075 Inches 



5/4" 05 Inches .095 inches 



6/4" 06 Inches .115 inches 



8/4" , 08 Inches .155 inches 



The above example may serve your purpose, but it is based on the 

 assumption that the green lumber was sawed to the exact dimension, and 

 the tigurcs for shrinkage are average for a great number of careful tests 

 anil might not apply exactly to any particular board. 



flartlwood takes in every variety of species, and the writer finds? that 

 all hardwoods do not shrink alike. Furthermore, you do not state whether 



This also, of course, makes a 



the stock Is to be bastard or (pmrtered. 

 dltference. 



It Is well known that wood shrinks twice as much tangentlally as It 

 does radially. Of course, this all depends on the way your stock la to be 

 sawed. 



Now, for instance, oak to be 1" thick when kiln-dried should be cut to 

 allow 4.1 per cent for shrlnkiige, when It Is green from the saw, and this 

 shrinkage in a laillal direction. t>n the other hand, an albiwance of 

 about 8 per cent should be made In the tangential direction. 



Now, to make this more clear : Suppose we had a piece of stock gi'een 

 from the saw to be kiln-dried to 1". If the piece was of bastard cut, we 

 would allow 4.1 per cent of 1" for shrinkage. If the piece was 2" on the 

 same kind of a cut, we would allow again 4.1 per cent of 2". The writer 

 believes this brings the allowance out better than in the other case. 



Now. stock ten months' air-dried, to be dried to 5 per cent molsure con- 

 tent in kiln, should have an allowance of 3 per cent In the radial iltrec- 

 tlon and 6.3 per cent in the tangential direction — this being oak. 



Now, these shrinkages vary according to the species, but in general 

 you will find that this will cover pretty much all species. 



From Forest Products Laboratory, Madison, Wis. 



'J'hc <picstlon you ask is one which cannot Iw ;inswered in a few words. 

 So far as we know it is impossible to tie this matter down to definite 

 figures applicable in all cases. As you undoubtedly know, the Naticmal 

 Hardwood lumber rules state that the lumber shall be of standard thick- 

 ness when shipping dry. However, the state of dryness known as "ship- 

 ping dry" has, so far as I know, never been defined In any definite usable 

 way. I presume that one would be safe in making the general statement 

 that hardwoods which have been alr-ilrled ten months are at least ship- 

 ping rlry and that, therefore, according to the National rules, the thick- 

 ness should be just about stamhird or a trifle less. 



The exact moisture in stock which has been seasoned for any given 

 period will vary tremendously, of course, with weather changes as well as 

 with the coTKlition (d' the stock itself and the species, .\ssumiug that the 

 moisture content of shipping dry stock is 20 per cent and that kiln-dried 

 stock contains 7 per cent moisture (these assumptions will probably apply 

 reasonably well to most conditions), the shrinkage from shipping dry to 

 kiln dry will be approximately one-half of the total shrinkage from green 

 to oven dry. In other words, it will be about half of the shrinkage which 

 you will find in table 2 of Bulletin 552. On this basis, taking, for example, 

 the first species appearing in the list, namely, red alder, quarter sawn 

 stock of standaril size when shipping dry will be one-half of 7.3 or 3.65 

 per cent undersize in thickness when kiln-dried, and slash-sawed stock 

 would be one-half of 4.4 or 2.2 per cent undersize. Individual pieces would, 

 of course, be expected to vary considerably from this average. 



Railroad Tie Production 



The normal demand for railroad ties is somewhere, between 100 million 

 and 125 million annually, says the recent U. S. Forest Service report com- 

 piled In response to the Capper Resolution in the Senate. In 1918, pur- 

 chases were slightly under 77,500,000 according to the report, and in 10 

 months of 1919, were slightly over 84.300,000. During the war and the 

 period of Government supervision of the railroads, extensions could not be 

 made and improvements were neces.sarily confined to those of an urgent 

 character. Lumber purchases were therefore at a minimum. Even under 

 such a policy of retrenchment railroad purchases of sawed materials, ex- 

 cluding hewn railroad ties, telephone poles, etc., aggregated approximately 

 4% billion feet or 14 per cent of the total lumber cut of the country 

 for 1918. 



That there have been profound changes In the lumber distribution from 

 different regions during the past year, continues the report, is shown by the 

 invasion of the Middle Western and Eastern States by Douglas fir ties. 

 These are regions which in the past have heen supplied with the standard 

 oak tie cut immediately along the rights of way or with southern pine 

 ties from the South. During 1919 orders amounting to nearly 100,000.000 

 board feet were placed for Douglas fir ties for eastern roads because of the 

 uncertainty of securing adequate supplies along their rights of way and 

 because of the excessive costs of local ties. In other words, oak ties cut 

 within a few miles of the right of way and bearing practically no charges 

 In freight and southern pine ties are now being replaced by fir ties hauled 

 overland across the continent or shipped through the Panama Canal. 



The results of this and similar journeys have added to the conviction pf 

 lumbermen that aircraft was extremely useful In the timber industry. 

 In the woo<ls of northern Quebec alone this season, 4.000 miles have lieen 

 explored In flying trips. A complete camping outfit is carried on these 

 flying boats, including a tent, canoe and a plentiful supply of food. 



