KILN DRYING HANDBOOK 55 
circulation and an accurate control of both temperature and 
humidity. 
The two schedules following, Tables 8 and 9, have given good re- 
sults. The drying time under them will vary considerably with the 
size and the shape of the stock. For 1-by-8-inch material it should 
be about 82 hours, to secure a final average moisture content of 15 
per cent. 
TABLE 8.—Special kiln-drying Schedule 103 for Douglas fir* 
Dry-bulb| Wet-bulb Relative 
Time in the kiln at which conditions shall be established tempera- | tempera- Ses 
humidity 
ture ture 
ae O Jat, Per cent 
IBesINnIne- OnTuUn Gnitial conditions) =. 422582 ke a eee 175 160 70 
1 For general use with the following sizes: 1 by 6, 1 by 8, 2 by 4, and 2 by 6 inches. 
TABLE 9.—Special kiln-drying Schedule 104 for Douglas fir* 
Dry-bulb| Wet-bulb Relative 
Time in the kiln at which conditions shall be established tempera- | tempera- Huanait 
ture ture y 
OER oD) J Per cent 
BesinNMINexOL TUS GMit1al COMGIELOTS) 2 ee ah ne ee UN ALN ayaa 175 166 80 
FEATVG EO Lehi Gala lt fe Teh TT te AE ER RN ed) AU Sa AS 175 160 70 
1 For general use with the following sizes: 1 by 10. 1 by 12, 2 by 8, 2 by 10, and 2 by 12 inches. 
The falling out of knots causes more degrade in 1-inch common 
lumber (especially No. 1 Common) than in other thicknesses of 
Douglas fir, and one of the mills kiln-drying large quantities of this 
stock has developed a special schedule for it. Under the schedule 
the drying temperature is kept constant at 125° F. and the humidity 
at 70 per cent; the kilns furthermore are operated on a flat time 
basis, each charge being dried 48 hours. In kilns with reversible 
circulation a single reversal at the 40-hour point is sufficient. The 
degrade experienced with this schedule is very small indeed. 
This same mill uses a more severe schedule for 2-inch common 
lumber, with which the drying is completed in the same time, 48 
hours. The drying temperature is kept constant at 175° F.; the 
humidity for the first day is 62 per cent and for the second day 53 
per cent. With reversible circulation kilns a single reversal at the 
40-hour point is sufficient. 
Kiln drying wide, flat-grain finish lumber without surface check- 
ing is rather difficult. On account of the value of this stock, how- 
ever, drying it with extreme care pays well. The schedule recom- 
mended for this service, Division IV of No. 00, is a good one for 
average conditions, but where the very minimum of degrade is 
desired the special schedule of Table 10, also developed by the same 
mill, may be used. 
