128 FOREST PRODUCTS 



each loo ft. by i8 ft. in dimension. Until within recent years, air 

 drying was resorted to entirely to properly season the heading boards. 

 Kiln drying has the advantages of saving in time and the control of the 

 dry condition of the boards. Softwoods may be kiln dried directly from 

 the heading saw and planer, but hardwoods should first be air dried for 

 from ten to thirty days, depending upon the kind of wood and the 

 season. 



Fig. 31. — Heading sawing machine. 



In a heading mill, which turns out from 2500 to 4000 sets of beech, 

 birch and maple heading per day, there are two dry kilns 128 ft. long, 18 

 ft. wide and 10 ft. in height. Each kiln has a capacity of 20 cars, each of 

 which holds from 4500 to 5000 pieces. Every effort is made to dry all 

 the boards, which are separated by stickers, at the same rate, to prevent 

 warping, checking and case-hardening. Many plants use a series of 

 steam pipes to secure and regulate the proper amount of heat and a 

 forced draft over the cars is provided bv a large fan. At one mill, at the 



