74 FOREST UTILIZATION 



the band saw and the poorest to the gang saw. 

 Two edgers and one trimmer can take care of such 

 a combined output, 

 (b) Mammoth mills are now considered uneconomical, 

 since it is difficult to take care of the output of 

 boards at the outlet from the mill floor. 

 The output per mill hand in big concerns is up 



to 7,5Co board feet daily. 

 Four acres of mill pond hold up to 1,000,000 board 



feet. 

 Two standard ga,uge trains supply an output of 

 100,000 board feet from an average distance of 

 10 miles, daily. 

 B. The carriage. 



I. The composing parts are: 



The truck with head blocks, knees, dogs, set works, and 



the driving machinery. 

 The carriage is subject to the roughest treatment. Still, 

 its proper alignment is as essential as that of the saw. 

 (a) The truck is made of timber at least 6 inches 

 square, thoroughly seasoned and strongly braced 

 and bolted. 

 Construction material is : 



Up North — Norway pine, birch and maple. 

 Down South — ^ Yellow pine and white oak. 

 The length should correspond with the maximum 



size of logs. 

 So called screw block trailers may be added, in- 

 creasing the length (in longleaf pine mills) up 

 to 72 feet. 



(b) The head blocks, iron with steel face, are let into 



the timbers of the truck and form a groove for 

 the tongue of the knee, which slides on the head 

 blocks, being moved forward and backward by 

 the set works. 

 The head block and knee form a right angle into 

 which the log is firmly pressed. 



(c) The knee is either solid or hollow and carries the 



dogs. 

 The dogs are hooks or clamps or teeth, meant to 



grasp the log. They are fastened either inside 



or outside of the knee. 

 Two tooth 'bars, playing inside the hollow knee 



and pressed by a powerful lever, replace the 



original dogs in modern mills. 

 "Underdogs" are used in quarter sawing. 

 The number of head blocks, knees and dogs is 



variable. The minimum is two of each. 



